Electronic Theses, Dissertations, and Records of Study (2002– )

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Description

This collection contains Texas A&M University theses and dissertations written after 2002.

History

In 2002, the Texas A&M University’s Office of Graduate and Professional Studies (OGAPS) began accepting electronic submission of theses and dissertations. In 2004, electronic submission became a requirement, and OGAPS now also accepts electronically submitted records of study.

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Most theses and dissertations in this collection are open access. However, Texas A&M University students have a right to place their work under embargo in certain circumstances. The full-text of theses and dissertations under embargo is restricted until the embargo period has expired.

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    Modeling Study of Precursor-specific Secondary Organic Aerosol and Organic Tracers
    (2021-10-01) Zhang, Jie; Ying, Qi; Chellam, Shankararaman; McKay, Garrett; Liu, Xiaohong
    In this study, the community multiscale air quality (CMAQ), with modifications to track precursor-specific SOA, was applied to model SOA and organic tracer formation from aromatic compounds, isoprene, monoterpenes, and sesquiterpenes. The model predicted aromatic and monoterpene SOA showed strong correlations with the measured daily corresponding organic tracers, which indicates that the tracer-method is a good approach to evaluate model predictions in precursor-specific SOA. However, the tracer-to-SOA ratios (fSOA (italicized)) derived from the modeling results show large variation based on different SOA components considered, and the fSOA (italicized) values showed significant difference from those determined in chamber experiments due to the difference between chamber conditions and ambient atmosphere. The fSOA (italicized) in the ambient air can be assessed by the modified CMAQ model with abilities to simulate organic tracers and SOA simultaneously. The modeled aromatic SOA tracer, 2,3-dihydroxy-4-oxopentanoic acid (DHOPA), agree well with the field measurements (MFB = 0.15; R = 0.8), and approximately two-thirds of it is from the oxidation of toluene. The modeled fSOA (italicized) shows a strong dependence on the OA loading when only semivolatile aromatic SOA components are included, while this dependence becomes weaker when non-volatile oligomers and dicarbonyl SOA products are considered. To predict total aromatic SOA, a constant fSOA (italicized) of 0.002 is determined, and the common-used chamber-determined fSOA (italicized) value of 0.004 could lead to an underestimation of SOA by a factor of 2. The isoprene-SOA scheme in the CMAQ model is expanded to simulate the unique isoprene tracers 2-methyltetrols (2-MT) and 2-methylglyceric acid (2-MG) by treating them as semivolatile species and including a non-heterogeneous formation pathway. The modeled fSOA (italicized) of sum of 2-MT and 2-MG in the total isoprene-SOA varies gently, between 0.01-0.02 in polluted regions, suggesting that the chamber-determined fSOA (italicized) of 0.063 may lead to large underestimations of overall isoprene SOA. The monoterpene (MT) and sesquiterpene (SQT) SOA was simulated by the CMAQ model with five explicit and one lumped MT species and SQT, and the contribution from each oxidation pathway was tracked in the MT SOA formation. Three MT tracers (pinic acid, PA; pinonic acid, PNA; and 3-methyl-1,2,3-butanetricarboxylic acid, MBTCA) and one SQT tracer (β-caryophyllinic acid, BCARYA) were modeled to assess the fSOA(italicized) values to estimate MT and SQT SOA. The fSOA (italicized) shows significant OA dependence, suggesting that using a constant fSOA (italicized) could lead to large errors in estimating terpene SOA. Instead, power-law equations directly link the tracer concentrations to the corresponding SOA concentrations were proposed and lead to good SOA estimations.
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    Well-Balanced and Invariant Domain Preserving Schemes for Dispersive Shallow Water Flows
    (2021-12-17) Tovar, Eric Joseph; Guermond, Jean-Luc; Bonito, Andrea; Popov, Bojan; Ragusa, Jean
    As urbanization encroaches more on flood prone regions and paved surfaces are ever expanding, more catastrophic flash floods occurring in urban environments are expected in the near future. These risks are compounded by global changes in the climate. Mathematics can help better predict and understand these situations through modeling and numerical simulations. The aim of this work is to discuss current mathematical and computational issues in modeling shallow water flows with applications in coastal hydraulics, large-scale oceanography and in-land flooding. Our mathematical starting points are the systems of partial differential equations known as the (i) Saint-Venant shallow water equations and (ii) dispersive Serre–Green–Naghdi (SGN) equations. The goal of this work is to efficiently solve both mathematical models supplemented with external physical source terms for in-land flooding and large-scale coastal oceanography applications. In particular, the work focuses on introducing a novel technique for solving the Serre–Green–Naghdi equations. We introduce new analytical solutions of the SGN equations with topography that are used to verify the accuracy of numerical methods. Then, we propose a new relaxation technique for solving the SGN equations with topography effects that yields a hyperbolic formulation of the equations. This relaxation technique allows us to circumvent the dispersive time step restriction of the Serre Equations which is a major challenge when solving the equations. This method is then supplemented with a novel continuous finite element approximation that is second-order accurate in space, invariant domain preserving and well-balanced. The method is then verified with academic benchmarks and validated by comparison with laboratory experimental data.
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    Environmental Effects on Viable Virus Transport and Resuspension in Ventilation Airflow
    (2021-12-02) Baig, Tatiana; King, Maria D; Fernando, Sandun; Kimber, Mark
    Currently little is known on how SARS-CoV-2 spreads indoors and its infectability. The objective of this study is to gain more knowledge on the effect of environmental factors on the spread and infectivity of virus aerosols in the built environment. Understanding how the virus transmits indoors would allow for early detection and mitigation of viral particles in room sized spaces. Bovine coronavirus (BCoV) was used as virus simulant in laboratory experiments conducted in a controlled humidity cabinet at Biosafety Level 2. An air-jet nebulizer was used to disseminate known numbers of BCoV particles. After aerosolization, the surface in the cabinet was swiped at regular time intervals to assess the number of particles impacted. Additional surfaces placed in the chamber and swiped at the end of testing. The samples were quantified using quantitative polymerase chain reaction (qPCR). Virus attachment to the surfaces was analyzed using bio-layer interferometry. The virus aerosols that remained suspended in the air were collected bioaerosol collectors with a reference air sampler and quantitated by qPCR. To monitor the effect of the ventilation on the virus movement, PRD1 bacteriophage aerosols as virus simulants were also disseminated in a ¾ scale ventilated hospital test room equipped with twelve PM2.5 samplers at 15 L/min. After plating and counting the plaque forming units (PFU), the highest concentration of viral particles was detected above the patient’s head in the test room in the second ventilation configuration. Other high virus concentration locations were near the foot of the patient’s bed. From these results, it was determined that with the current airflow set up in the second configuration with the air inlet on the ceiling above the bed, exhaust bottom left on the wall behind the bed, the virus particles concentrate over the lower part of the patient’s bed. Based on air property measurements, aerosol collections and the mechanical blueprint of the model room, a computational flow model was created to visualize the entrainment and movement of the virus in the ventilation airflow. The models showed the third presented configuration minimized particle concentration at the door while the first configuration decreased overall particle concentration in the room.
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    Effectiveness of Geocell Reinforced Reclaimed Asphalt Pavement Base Layer for Flexible Pavement System over Expansive Subgrades
    (2021-12-01) Khan, Md Ashrafuzzaman N/A; Puppala, Anand; Lytton, Robert; Aubeny, Charles; Rybkowski, Zofia
    The transportation agencies must allocate a significant annual budget to rehabilitate low to high volume roads constructed over expansive subgrades. This type of subgrade soil undergoes substantial changes in volume due to the seasonal fluctuation of moisture levels, which will lead to pavement distress, including rutting, heaving, or/and longitudinal cracking. On the other hand, utilizing the large volume of reclaimed asphalt pavement (RAP) aggregates as a part of the pavement base layer has been a big challenge for researchers due to its poor mechanical properties. The traditional subgrade treatment procedures with full-depth reclamation are cost-intensive and time-consuming. Therefore, the transportation industry looks for an economical and sustainable alternative to address both these issues. This research study aims to assess the potential benefits of a three-dimensional confinement system, commercially known as “geocell,” to improve the performance of RAP materials and provide consistent support to the flexible pavement structure constructed over expansive subgrades. This dissertation focused on contributing to the field of pavement geotechnics in two ways: first, to evaluate the performance of the geocell reinforced RAP-base (GRRB) layers to improve the performance of the flexible pavement constructed over expansive subgrade soil; and second, to develop a design methodology for such pavements based on field observations, cost and sustainability assessments. Several test sections were constructed over an existing farm-to-market road, FM 1807, which suffered from distresses induced by the underlying expansive subgrade. These test sections were designed and constructed with different geocell-RAP infill materials, instrumented with sensors including Shape Array Accelerometers (SAAs) and Earth Pressure Cells. The structural capacities of the pavement sections were further evaluated by performing nondestructive field tests, including Falling Weight Deflectometer (FWD) and Automated Plate Load Test (APLT). In addition to the field testing, numerical modeling analyses were performed to understand the contributions from the geocell bases and determine the future load-carrying capacity based on compressive strain acting on the subgrade soil. The expected design life of the geocell-reinforced pavement was calibrated with the field monitored data, and these results are used to develop flexible pavement design on expansive soils by utilizing a GRRB layer. The economic and sustainability aspects of flexible pavements with GRRBs are further verified with Life-Cycle Cost Analysis (LCCA) and sustainability analysis. It is believed that this research study will provide future practical guidelines for the construction and design of flexible pavements with GRRBs over expansive subgrades.
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    Temperature-Responsive Poly(Vinyl Alcohol)-Borax Salogels for Shape Stabilization of an Inorganic Phase Change Material
    (2021-09-28) Zhu, Xiuzhu; Sukhishvili, Svetlana; Pentzer, Emily; Shamberger, Patrick; Lutkenhaus, Jodie
    A temperature-responsive gel has been introduced to achieve shape stabilization of phase change materials (PCMs). Inorganic salt hydrates are promising PCMs, but their low viscosity at temperatures above their melting point leads to leakage and corrosion in thermal storage modules. Temperature-responsive salogels can trap inorganic salt hydrates to achieve shape stabilization when the temperature is lower than the gel-sol transition temperature (Tgel) to overcome the leakage problem. Increasing the temperature above Tgel transforms the system to the liquid state enabling easy removal of the PCM material from the thermal storage units. This work focuses on the salogels system consisting of poly(vinyl alcohol) (PVA) dissolved in calcium nitrate tetrahydrate (CNH). Through variations in molecular weight, degree of hydrolysis, and concentration of PVA, precise control of Tgel of the salogel was achieved. Importantly, at the matched PVA concentrations, gelation occurred in CNH but not in water. This difference is rationalized by the unique features of CNH as a solvent, such as an extremely high salt content and scarcity of water. Interactions of PVA and solvent were investigated using attenuated total reflection Fourier Transform Infrared spectroscopy (ATR-FTIR), and a suggested mechanism of gelation of PVA in CNH is discussed. To further enhance the salogel strength and improve control over the gelation temperature, borax as a crosslinker that forms dynamic covalent bonds with PVA was introduced. PVA/borax/CNH salogels could achieve Tgel as high as 70°C using 3 wt% PVA and as low as ~0.3 wt% concentration of borax. The crosslinking mechanism of borax and PVA in CNH involves formation of dynamic covalent borate ester bonds, which lead to salogel strengthening. Compared to traditional PVA-borax hydrogels in water, PVA-borax salogels in CNH showed the unique feature of highly repeatable temperature reversibility. In addition, the reported salogels not only provide shape stabilization of CNH but also exhibit robust self-healing properties.
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    VOF with Center of Mass and Lagrangian Particles (VCLP) - A Surface Tracking and Advection Method for Fluids
    (2021-12-07) Chizhuthanickel Sunny, Richards; Horrillo, Juan J; Chen, Hamn-Ching; Perlin, Marc; Koola, Paul M
    This dissertation presents a novel surface tracking, and advection algorithm for incompressible fluid flows in two and three dimensions. This method based on the volume-of-fluid (VOF) method, is named VOF-with-center-of-mass-and-Lagrangian-particles (VCLP), and it uses spatially and temporally localized Lagrangian particles (LPs) inside a finite volume framework. The fluid surface is recaptured and reconstructed piecewise using the mean slope, mean curvature, and fluid estimated using new methods from the local spatial distribution of the volume fluid fraction values. The reconstructed surfaces are either a finite plane or part of a spherical surface, in 3D and line segments or circular arcs, in 2D. The fluid mass inside each cell is discretized spatially by LPs and distributed as blue noise. LPs are then advected cell by cell with a choice of two different advection schemes in time using interpolated velocity and approximated acceleration fields. VCLP continuously tracks the center of mass of the fluid parcels in the Lagrangian way and this helps to reduce the errors due to numerical acceleration resulting from lack of information to reconstruct the interface accurately. LPs enable VCLP to work with structured and unstructured grids in two and three dimensions and might work for Courant–Friedrichs–Lewy numbers larger than one. LPs exist only inside a single fluid cell at a given time-step, allowing it to work without constraints on domain size and storage memory, unlike standard Lagrangian methods. LPs make it easy to adjust computational accuracy vs. speed by only changing the number of LPs. VCLP’s performance is evaluated using standard benchmark tests such as translation, rotation, single vortex, deformation, and Zalesk’s tests from the literature. VCLP is applied to TSUNAMI2D, a 2D Navier-Stokes model to simulate the dam-break problem and breaking waves.
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    Developing a Three-Dimensional (3D) Bioprinted Tumor Model
    (2021-12-02) Nayak, Biswadeep; Gaharwar, Akhilesh; Adjei, Isaac; Bayless, Kayla
    High phenotypic heterogeneity in tumor cell population, especially with glioblastoma stem cells (GSCs), is one of the major causes of poor prognosis of malignant glioblastoma (GBM). Although in vivo drug screening using tumor spheroids and animal models can provide insights about structural heterogeneity, their inability to recapitulate the tumor niche and phenotypic heterogeneity limit their translation to the clinic. Development of an in vitro 3D bioengineered model that can recapitulate the native brain niche has the potential to study GBM malignancy. In the present study, we aimed to develop a reproducible bioprinting method to fabricate a physiologically relevant biomimetic GBM tumor model. Towards this aim, we synthesized a brain extracellular matrix (ECM) mimicking gelatin methacrylate (GelMA) bioink with modulated concentration of chondroitin sulfate (CS), a major source of glycosaminoglycans (GAGs) in the brain tissue. Bioprinted constructs of GBM spheroids with integrated brainspecific microenvironmental cues showed intact morphology, high viability and metabolic activity, and enhanced invasion.
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    Heavy Ion Beam Diameter Reduction for Single Event Effects Testing of Semiconductor Devices
    (2021-12-10) Blezinger, Dylan Cade; Fink, Rainer; Martinez, Jose Silva; Hung, Wayne
    Single Event Effects (SEE’s) are a common phenomenon in high-altitude semiconductors applications. SEE’s are primarily caused by a single ionizing particle, in this case, a heavy-ion striking a single transistor within the Integrated Circuit (IC), causing irregular behavior or device operation. In space environments, high-energy ionizing particles have the potential to jeopardize a mission due to critical computer failure as well as introducing undesirable device operations. SEE’s become more common and critical with new semiconductor designs that have a higher transistor density, as the ionizing particle has a greater probability of interacting with a single transistor. Currently, companies such as Texas Instruments Inc. test the effects of high-energy ionized particle strikes on new integrated circuit designs using the Texas A&M Cyclotron Institute K500 beamline. During the debugging process, specific sections of the DUT must be evaluated with the particle beam, while the remaining portion of the DUT is shielded. The current solution is tedious, inaccurate, and not well understood, resulting in wasted critical reactor time. The current research project describes a system that increases the accuracy of transistor targeting, improves radiation beam diameter reduction, and reduces setup time. The system described was developed in close collaboration with a parallel project providing microscopy and precision alignment.
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    From Tuberculosis Diagnostics to Therapy: Development of a Tail Fiber Protein-Derived Microfluidic Diagnostic Device and Utilization of Synergistic Properties of Antimycobacterial Drugs
    (2021-12-09) Rousseau, Simon; Pellois, Jean-Philippe; Polymenis, Michael; Gill, Jason; Rye, Hays
    Tuberculosis, the disease caused by the mycobacterial pathogen Mycobacterium tuberculosis, has been, prior to the COVID-19 pandemic, the world’s deadliest infectious disease. The illness has been afflicting humans for centuries, and despite decades long efforts to eradicate it and the availability of curative treatment options, tuberculosis remains prevalent across most of the globe. According to the WHO Tuberculosis Reports, approximately 1.7 billion people are estimated to be infected by the bacteria and 1.5 million people die from the disease every year. Effective diagnostics and treatment are key to combating any infectious disease pandemic and in this work, we present a novel approach to improving both. We created a magnetophoretic microfluidic device which uses recombinant mycobacteriophage tail fiber proteins bound to magnetic nanoparticles to pull down mycobacterial cells, selectively concentrating the cells before performing a diagnostic microbiological stain protocol. We have shown that we could lower the limit of detection of Mycobacterium tuberculosis from a synthetic sputum sample by 6 to 26-folds per milliliter of sample, without significantly altering the process used at point-of-care clinics. We also investigated the synergistic interactions between drugs, which we believe is a key element to improving efficacy of drug regimen, but also for the creation of new drug combinations, specifically designed to work together. We have shown that using low doses of Bedaquiline causes inhibitors of PEPCK to be synthetically lethal, despite their lack of whole cell activity on their own. This suggests that typical drug discovery campaign may be missing some valuable compounds, that could play an important part of a combination regimen. Furthermore, we have synthesized the necessary substrate required for the development of an enzymatic assay for peptidyl tRNA hydrolase. This assay could then be used to identify inhibitors of PTH, which could restore Mtb sensitivity to macrolides. These drug discovery campaigns seek to make a better use of synergistic drug interaction and use this information as an integral part of drug discovery.
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    Evaluation of the Effects of Printing Parameters and New Bioink Composition on Green Bioprinted Constructs
    (2021-12-01) Jerpseth, Laura Renee; Qin, Hongmin; Pei, Zhijian; Bell-Pedersen, Deborah
    Bioprinting is an additive manufacturing process capable of fabricating bioprinted constructs containing cells via layer-by-layer deposition of bioink. Bioink contains the cells using during bioprinting, and may contain additional materials to promote cell adhesion, cell viability, structural integrity, and/or shape fidelity of bioprinted constructs. While bioprinting using mammalian cells has been extensively studied, less research has been conducted regarding bioprinting using photosynthetic cells, also known as green bioprinting. Potential benefits of green bioprinting include production and easy harvesting of metabolites for use in the pharmaceutical, cosmetic, and food industries. Constructs fabricated using green bioprinting have also been shown to remove metal from water, and green bioprinted constructs are capable of providing oxygen to mammalian cells in order to supplement tissue engineering research. Despite potential benefits, more research is required to determine the optimal printing parameters for green bioprinting. In order to be functional, bioprinted constructs must have high cell viability post bioprinting. Research was conducted to test the effects of variable extrusion pressures and needle diameters on Chlamydomonas reinhardtii algae cell viability in green bioprinted constructs. It was determined that increasing extrusion pressure and decreasing needle diameter decreased the cell viability in green bioprinted constructs. Additionally, in currently published literature, only two bioinks have been used for green bioprinting applications. These bioinks, alginate:methylcellulose and alginate:agarose:methylcellulose, promote high photosynthetic cell viability. However, the bioinks do not have sufficient physical properties to bioprint constructs with high shape fidelity. A new bioink, alginate:methylcellulose:GelMA, was synthesized to improve the shape fidelity of green bioprinted constructs while maintaining high cell viability. Constructs bioprinted with alginate:methylcellulose:GelMA bioink were tested for Chlamydomonas reinhardtii algae cell viability and shape fidelity of the bioprinted constructs. Rheological analysis was also performed of a sample of unprinted alginate:methylcellulose:GelMA bioink to determine if the viscosity of the bioink is suitable for use with bioprinting. It was determined that alginate:methylcellulose:GelMA bioink has suitable viscosity, and can be used to bioprint green constructs with high cell viability and shape fidelity.
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    Teleoperated Positioning and Microscopy System for Diagnostic Single-event Effects Testing of Integrated Circuits
    (2021-12-08) Wedelich, Jackson Douglas; Fink, Rainer J; Song, Xingyong; Silva-Martinez, Jose
    The semiconductor industry is engaged in a process of innovation for space applications. Trends in space exploration and satellite technology are driving requirements for processing power higher and constraints for integrated circuit (IC) size lower. The processes for characterization and testing for radiation hardness of semiconductor devices, governed by the United States Department of Defense, remains focused on single-event effects and total ionizing dose at the level of an entire IC. Though these standards effectively give consumers the information and quality they need, simply testing to these standards does not enable effective innovation for designers of the devices. In the process of characterizing the radiation hardness of ICs, it is useful to isolate radiation exposure to individual functional blocks within a circuit. This radiation isolation testing can lead to discoveries of varying vulnerabilities in functional blocks of an IC. Radiation isolation testing is time consuming and costly because of the tedious process and repetitive actions required. This project combines mechanization of the existing process with remote operation capabilities to reduce repetitive actions and expand the capabilities of radiation isolation testing. This document covers the requirements of the system and its successful implementation.
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    3D Printing-Based Manufacturing Method for Biomass-Fungi Composites
    (2022-01-04) Bhardwaj, Abhinav; Pei, Zhijian; Zou, Na; Shaw, Brian; Wolff, Sarah
    Biomass-fungi composites represent a sustainable material with applications in the construction and packaging industries. Currently, molding is used to manufacture biomass-fungi composite products. 3D printing of these composites would facilitate greater design flexibility for various construction and packaging applications. This dissertation presents a novel 3D printing process for the manufacturing of products using these composites. It includes the mechanical processing and employing a printability aiding additive to facilitate 3D printing. Mechanical mixing was used to convert the loose, biomass-fungi material into a liquid slurry. Psyllium husk powder was used as a printability aiding additive that prevented phase segregation during the printing process thereby avoiding problems such as nozzle blocking. The appropriate amount of printability aiding additive was also determined by analyzing the print quality of mixtures varying in the content of this additive. The rheological properties of these mixtures have also been discussed. The effect of mixing process parameters (such as mixing time and mixing type) on fungal growth has been studied. Furthermore, this dissertation also presents the effects of printing process parameters (such as print speed and air pressure) on fungal growth. Lastly, the tensile and compressive strength data of these composites has been presented.
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    Development of a Hybrid Model and Optimal Control Algorithm for a Full-Scale Bio-Fermentation Process
    (2021-11-30) Shah, Parth J; Kwon, Joseph; Kravaris, Costas; Gildin, Eduardo
    Bio-fermentation process is difficult to model given its use of living micro-organisms to produce useful products via complex reaction mechanisms. Their kinetics are hard to characterize; hence, approximate formulations are used when building a first-principles model. Consequently, such a model will be of poor accuracy. Recently, there is a lot of interest towards data-driven modeling as the amount of data collected, stored, and utilized is growing tremendously due to the advent of super-computing power and data storage device. Additionally, data-driven models are simple and easy to build but their utility is hugely restricted by the amount and quality of data used to develop them. Therefore, hybrid modeling is an attractive alternative to purely data-based modeling, wherein it combines a first-principles model with a data-based model resulting in improved accuracy and robustness. In this work, we develop a three-step method to build a hybrid model for a full-scale bio-fermentation process with a volume of over 100,000 gallons. Firstly, we improved the accuracy of the first-principles model via incorporating mathematical terms in its equations which are based on obtained process knowledge from a literature study. Secondly, we performed local and global sensitivity analysis to identify sensitive parameters in the improved first-principles model that have considerable influence on its prediction capability. Finally, we developed a deep neural network (DNN) based hybrid model by integrating the improved first-principles model with a DNN which is trained to predict the identified model parameters. The resulting hybrid model is more accurate and robust than the (original and improved) first-principles models as it is equipped with a trained DNN to predict the uncertain parameters and process states accurately. Based on the developed hybrid model, a hybrid model-based observer was developed to track the different states present in the process. As the available measurements were fairly accurate, the open-loop observer was re-initialized with a new set of measurements whenever they become available. This method is computationally less demanding and was able to accurately estimate the states. Next, we build an optimal control algorithm on GAMS software to estimate the optimal operating conditions of the fermenter in real-time. This is carried out in order to maximize the product amount and minimize the cost by manipulating the inputs and taking practical constraints into account. The resulting control algorithm was able to improve the profitability and the productivity of the full-scale bio-fermentation process.
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    Quality-centric Authentication of Additively Manufactured Parts through Voronoi-based Error Exaggeration
    (2021-11-29) Adhikari, Riddhi Ramesh; Krishnamurthy, Vinayak R; Akleman, Ergun; Tai, Bruce L
    Additive manufacturing or rapid prototyping is continuously gaining popularity within and outside the research community. Due to its growing applications and technical and economical advantages over conventional machining, additive manufacturing is being used even to manufacture critical components in aerospace and automobile industry. As a result, there is also an increase in counterfeiting in this technology which can pose a threat to proprietary parts. This research work deals with authenticating 3D printed parts by comparing the quality of the parts with the precision and bias of 3D printers. The idea is to be able to differentiate between the error distributions of two printers so as to authenticate the parts printed on them. Therefore, the primary research goal of this work is to be able to quantify the differences in error distributions across different printers and characterization of printers. The key challenge is that it is difficult to robustly quantify the difference between two printers simply by comparing their coordinate error distributions. To address this challenge, we introduce a novel topological transformation based on the principle of Voronoi Tessellation, called SplitCode, that exaggerates the differences in coordinate error distributions, thereby, enabling us to better differentiate two given printers quantitatively. Consequently, the method leads to a robust authentication of 3D printed parts. In this work, through numerical simulations we study the effect of varying mean and standard deviation of error distributions on topological transformation. We find out that maximum exaggeration of the difference between error distributions is achieved on using length, angle and midpoint location to represent the split edge. We present a methodology for quality assessment and authentication and study the effect of different known distributions on authentication. On validating our scheme numerically, we learn that application of SplitCode improves accuracy of authentication between printers with same bias but different precision. Finally, experimental results show that authentication is possible between two printers with different biases both before and after application of SplitCode. However, authentication of lower quality parts printed on the same printer but at different speeds is influenced by the nature of error distributions of the printer and the print. In certain cases, application of SplitCode is required for authenticating prints that have same bias but different precision. The results of both simulated and experimental studies show that when the quality of the part changes and the problem is to identify a lower quality part, application of SplitCode results in better authentication. This highlights the quality-centric approach of authentication. This research work also offers various opportunities of further exploration in terms of part design, algorithm of SplitCode, imaging and post processing methods and statistical variations.
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    Bioactive, Self-fitting Scaffolds Prepared from Siloxane-based Shape Memory Polymers
    (2021-12-08) Beltran, Felipe Orlando; Grunlan, Melissa A; Shamberger, Patrick J; Gaharwar, Akhilesh K; Saunders, William B
    Thermoresponsive shape memory polymer (SMP) scaffolds afford conformal “self-fitting” into irregularly shaped craniomaxillofacial (CMF) bone defects. Grunlan and co-workers previously reported SMP scaffolds based on biodegradable poly(ε-caprolactone) (diacrylate) (PCL-DA). Later, to enhance the rate of degradation, semi-interpenetrating network (semi-IPN) scaffolds were formed with PCL-DA and thermoplastic poly(L-lactic acid) (PLLA) (75:25 wt%, respectively). Bioactivity (i.e., the ability to induce the formation of a layer of hydroxyapatite, HAp), a property integral to promoting bone regeneration, was imparted by coating scaffolds with polydopamine (PD). However, as the scaffolds erode, the PD coating is lost as is bioactivity. Furthermore, the impact of ethylene oxide (EtO) sterilization on such PD-coated scaffolds was not assessed. Grunlan and co-workers have previously observed that hydrogels containing siloxane-based polymers were bioactive. While PCL-based scaffolds had been previously prepared with a siloxane-based co-macromer, the bioactivity was not assessed. In the first study, PD-coated PCL-DA and PCL-DA/PLLA semi-IPN scaffolds were EtO sterilized. Morphological features, in vitro bioactivity, PCL crystallinity, PLLA crystallinity, and crosslinking were all preserved. Subsequently, shape memory properties, compressive moduli, and in vitro degradation behaviors were also unchanged. In the second study, to achieve self-fitting scaffolds with innate bioactivity, PCL/polydimethylsiloxane (PDMS) co-matrices were formed with three types of macromers to systematically alter PMDS content and crosslink density. PCL90-DA was combined with a linear-PDMS66-dimethacrylate (DMA) macromer, and a star-PDMS66-tetramethacrylate (TMA) macromer at 90:10, 75:25, and 60:40 wt % ratios. Scaffolds were also prepared with an acrylated (AcO) triblock macromer (AcO-PCL45-b-PDMS66-b-PCL45-OAc) (65:35 wt % ratio). All PCL/PDMS scaffolds displayed bioactivity in vitro, leading to significant increases in moduli. Furthermore, degradation rates increased with PDMS content. Lastly, the impact of siloxane polymer hydrophobicity on the bioactivity of PCL-based scaffolds was investigated. Scaffolds were prepared by combining PCL90-DA with either with linear macromers: PDMS66-DMA or polymethylhydrosiloxane66-dimethacrylate (PMHS66-DMA) (90:10, 75:25, and 60:40 wt % ratios). These PMHS-containing scaffolds exhibited further increased degradation and mineralized in just two weeks. Scaffolds were also cultured with human mesenchymal stem cells (hMSCs) to assess osteoinductivity. Compared to PCL-DA scaffolds, both PCL-DA/PDMS-DMA and PCL-DA/PMHS-DMA scaffolds had increased cell viability and proliferation as well as expressed higher osteogenic protein markers.
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    Modifications of Polyurethane Shape Memory Polymers for Medical Devices
    (2021-12-08) Fletcher, Grace Kiely; Maitland, Duncan J; Alge, Daniel; Haridas, Balakrishna; Staack, David
    Shape memory polymers (SMPs) are materials with the ability to undergo geometric change in response to a stimulus, also known as the shape memory effect. This shape memory behavior enables minimally-invasive delivery of medical devices, making SMPs of interest to biomedical researchers. Our group has extensively studied thermoset polyurethane SMP foams and modifications thereof to improve device performance. These gas-blown, low-density foams demonstrate high volumetric recovery and rapid hemostasis, making them particularly desirable for embolic applications. Another SMP thermoplastic polyurethane (TPU) material was previously developed by Hearon et al. This SMP system is currently underutilized, but it is highly tunable and processable, enabling control over polymer properties and architecture. This research provides a foundation for expanded future use of both polyurethane SMP systems (thermoset and thermoplastic) by addressing their major limitations for biomedical applications. There is a lack of inherent X-ray and MRI visibility with these polymeric materials, which can hinder device delivery and monitoring; therefore, a major goal was to modify the thermoset systems to achieve adequate visualization on X-ray and MRI modalities. Similarly, the TPU material system was modified to improve the X-ray visibility on molded parts. Drug delivery from a SMP matrix was explored for the intended use in breast cancer recurrence after tumor resection. Antimicrobial foams with modified antimicrobial triols and direct incorporation of antimicrobial agents were explored for use in hemostatic devices. Finally, in vivo use of the thermoset material is limited by its susceptibility to oxidation. Thus, the last goal was to improve the biostability of SMP thermoset foams.
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    Motion Planning with Discrete Geodesics
    (2021-12-09) Lopez, Thomas Jai; Gildin, Eduardo; Staack, David; Noynaert, Sam; Pate, Michael
    Several civil and military applications such as surveillance and reconnaissance require unmanned vehicles to visit targets while being optimized for travel time, fuel, and other communication and kinematic constraints. Unmanned vehicles could also have other limitations set by the size, the design, and the environment. This thesis considers discrete path planning problems for unmanned vehicles. The shortest continuous path for a constant speed vehicle from any arbitrary initial location and orientation to any arbitrary final location and orientation in the absence of obstacles takes the form of a Dubin’s path. While these paths are continuous and smooth, this thesis explores the case when the paths could be discrete instead. Dubin’s path is always one of the six kinds which could be an LRL. RLR, RSR, LSL, RSL, LSR; were L and R, are left and right turn arc segments respectively, and S is a straight-line segment. This thesis is concerned with similar paths except that the L and R, are left and right turn polygonal arc segments instead. Our work will prove that the discrete paths are shorter than their continuous counterparts. Moreover, the discrete paths are a more general form since they could generate the same results as the continuous counterpart when the polygonal arc chord length limits to zero. This is because a circular arc could be imagined as a polygonal arc with infinite edges. These paths are particularly relevant when we consider environments to travel with limited communication abilities. In GPS denied or GPS limited environments, performing discrete straight segment maneuvers are more reliable than traversing through circular arc segments especially since we do not have GPS feedback. Every vertex of the polygonal path could be imagined as ‘position’ (or ‘time’ when traveling in a constant speed) where the GPS location could be pinged for instead of relying on GPS feedback for the entire tour. The thesis characterizes the Discrete Geodesics with both non-inflection and inflection segments and presents explores algorithms. The work explores a more generic and beneficial version of the Dubin’s paths extended to study traveling salesmen problems.
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    Enhancing the Volumetric Effect of Point-Focusing Concentrating Solar Receivers via Partially Reflective Surfaces
    (2021-12-10) Salih, Fathya Yousif Mohamed; Kakosimos, Konstantinos; Abdala, Ahmed; Srinivasa, Arun A
    One of the remaining challenges of point focusing concentrating solar power systems is the realization of a true volumetric receiver, one whose entire volume is utilized for the absorption of irradiance. Current state-of-the-art receivers (e.g., HiTRec-II and SolAir-200) have not demonstrated the volumetric effect, because of low radiation penetration within the absorber. Earlier works have noted that radiation penetration can be improved by increasing porosity (void fraction), but at the cost of reducing the convective heat transfer area. More recent works have succeeded at improving radiation penetration in volumetric absorbers by axially grading the porosity of the structure, but those designs are complex and share the issue of manufacturability. Nevertheless, the improvements are notable and justify the pursuit of true volumetric receivers. This work discusses the conceptual design and numerical evaluation of a true volumetric receiver achieved by applying different reflectivity distributions to the irradiated surfaces to improve radiation penetration. The square honeycomb receiver structure was reduced to a single channel to allow for detailed modelling of radiative phenomena. Monte Carlo ray tracing was used to model external irradiance and the conventional direct integration approach was used to model mutual irradiance. This radiative model was coupled with a 3-dimensional heat transfer model and a laminar flow model for a complete description of the problem. Furthermore, the relationship between the axial reflectivity distribution and relevant design parameters like porosity and residence time are explored via parametric sweeps, with solar-to-thermal efficiency exit gas temperature and the volumetric effect ratio as the monitored responses. This work was completed using COMSOL Multiphysics®. The base case parametric study showed that the optimal parameters for a Silicon Carbide uniform reflectivity receiver are those of the HiTRec-II. Both varied reflectivity receiver cases considered exhibited an improvement in performance parameters for the same average emissivity of the base case. The best performance was achieved by a wall-varied reflectivity receiver, where every two walls were assigned a certain emissivity based on the amount of radiation they intersect. This receiver design is expected to achieve an increase of 5.2%, 6.1% and 8.2% in the exit gas temperature, thermal efficiency and volumetric effect, respectively, compared to the HiTRec-II.
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    Nonionic Surfactant Performance in High-Temperature Eagle Ford Reservoir
    (2021-12-08) Ladan, Elsie Bahati; Schechter, David; Akkutlu, Yucel I; Bhatia, Mukul
    The focus of this study was the use of nonionic surfactants and novel nonionic-ionic surfactant blends for enhanced oil recovery in high-temperature liquid-rich unconventional reservoirs. Through cloud point, wettability, IFT, and spontaneous imbibition experiments, 23 industrial surfactants samples (individual and blends) were investigated in an effort to design surfactant systems which could withstand temperature and pressure conditions from atmospheric up to 350˚F and 5000 psi. Although surfactants have proven successful and cost-effective in enhancing production from conventional and unconventional reservoirs, studies that used nonionic surfactants have been limited to reservoirs with temperatures below 200˚F due to the temperature-dependent physiochemical properties of these surfactants. Therefore, this study aims at designing surfactant blends for reservoirs like the Eagle Ford and Monterey formation in the US and the Embla field in Norway, whose reservoir temperature is above 300˚F. The effectiveness of the surfactants in reducing the interfacial tension (IFT) at the oil-brine boundary and restoring contact angle (CA) to water-wet (Ɵ < 75˚) were the critical factors in choosing the most appropriate systems. Results showed that the amount of ionic cosurfactant used affected thermal stability, with increasing concentration leading to increasing cloud point temperature (CPT). Wettability alteration was seen to be dependent not only on temperature but on the class of ionic cosurfactant. Cationic cosurfactants were observed to be better at improving the thermal stability of the nonionic surfactant. However, they resulted in oil-wet contact angles with increasing temperature. On the other hand, anionic cosurfactants displayed better synergy in terms of wettability alteration, creating strongly water-wet and intermediate contact angles at high temperatures. Therefore, focus was placed on nonionic-anionic surfactant blends for the reservoir sample used in this study. In the end, stable surfactant blends with cloud point temperatures from 316˚F to 348˚F were created for EOR applications in high-temperature conditions. Spontaneous imbibition studies using these blends indicated an improved recovery of up to 173%. Therefore, this work was successful in providing novel and cost-effective surfactant solutions for EOR in high-temperature conditions. This study ergo serves as a template for the surfactant screening and selection process to be undertaken when considering nonionic surfactants. And, valuable insight on the mechanisms of nonionic surfactant blends is provided to help in further design and application situations. The surfactant solutions designed for the reservoir under investigation produced tight emulsions, implying surface treatment will be required in some fields to deal with possible emulsions problems.
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    Characterization of Intermolecular Interactions Using Hyperpolarized NMR
    (2021-12-07) Mandal, Ratnamala; Hilty, Christian; Son, Dong Hee; Sheldon, Matthew; Cho, Jae-Hyun
    Nuclear magnetic resonance (NMR) spectroscopy is a widespread analytical technique used to characterize intermolecular interactions. However, due to the inherent insensitivity of NMR, long experimental times and large sample concentrations are required. Hyperpolarization methods are combined with NMR to broaden its application in characterizing intermolecular interactions rapidly. Here, hyperpolarization methods, based on Dissolution Dynamic Nuclear Polarization (D-DNP) and Para-Hydrogen Induced Polarization (PHIP) were developed to provide detailed interactions between proteins and small molecules. D-DNP was used to characterize the interaction between hyperpolarized lipid molecules and an unfolded Outer membrane X (OmpX) under refolding conditions for the protein. Cross-relaxation rates between the different functional groups in the lipid and OmpX were determined in the absence of any denaturant. The fast experimental timescale of D-DNP allowed to access these conditions and may be useful for investigating structural changes in proteins during the refolding process. The PHIP technique requires minimal instrumentation and can be a cost-effective hyperpolarization technique for characterizing biomolecular interactions. Signal Amplification by Reversible Exchange (SABRE), the non-hydrogenative variant of the PHIP, allows renewal of polarization in solution. The pool of biological ligand motifs hyperpolarized by SABRE was broadened by developing a method, which allowed to hyperpolarize ortho-substituted N-heterocyclic molecules. Previously, these molecules yielded low polarization due to hindered binding to the SABRE catalyst. This steric hindrance was solved by adding smaller coligand molecules that allowed the formation of the polarization transfer complex. The incompatibility of the SABRE catalyst in water and proteins in alcohol required to develop a two-step approach involving flow-NMR for characterizing protein-ligand binding. The ligand was hyperpolarized in methanol, and subsequently mixed with protein to characterize binding interactions in a predominantly aqueous medium. Changes in the transverse relaxation rate (R₂) in the presence and absence of protein was monitored to identify binding. Thereafter, the hyperpolarization of a molecule acting as a reporter ligand was used in a competitive binding experiment to find dissociation constants (KD) that differ in three orders of magnitude for various ligands. Using a single reporter ligand allowed to determine KD of ligands not hyperpolarizable by SABRE.