Missouri University of Science and Technology
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Nitrene-Transfer Chemistry To C-H And CโC Bonds Mediated By Triangular Coinage Metal Platforms Supported By Triply Bridging Pnictogen Elements Sb(III) And Bi(III)
Tripodal Ligands (TMG3trphen-E) That Feature Heavy Pnictogen Elements (E = Sb(III), Bi(III)) And Tetramethylguanidinyl (TMG) Arms Have Been Explored In Stabilizing Cu(I) And Ag(I) Sites And Facilitating Nitrene-Transfer Chemistry. Compounds [(TMG3trphen-E)M3(ฮ-X)3] (M = Cu(I), Ag(I); X = Cl, Br, I) Have Been Generated Upon Extraction Of M3(ฮ-X)3 Units From MX Sources, Exhibiting Support Of The Crown-Shaped M3(ฮ-X)3 Fragment By M-NTMG Bonds And Triply Bridging E โ M3 Interactions. Orbital Interactions Between Cu(I) Sites And NTMG Residues Are More Dominant Than Sb/Bi โ Cu3 Donor Interactions Between The Sb 5s Or Bi 6s Orbitals And Admixed Cu 4s/3d Orbitals, With Larger Interaction Energies Computed For Sb โ Cu3. Nonhalogenated Copper Compounds [(TMG3trphen-E)2Cu2]2+2Y- (Y = PF6, B(C6F5)4) Have Been Synthesized Via Dechlorination By TlPF6 Or By Application Of Halide-Free Cu(I) Sources With TMG3trphen-E Ligands. Nitrene-Transfer To Olefins Mediated By [(TMG3trphen-E)Cu3(ฮ-Cl)3] (E = Sb And Bi) Affords Aziridines In Good Yields, Primarily For Unencumbered Styrenes And With The More Robust Sb Catalyst. Amination Of C-H Bonds Is Most Effective With Sec-Benzylic Substrates And Requires A More Electrophilic Nitrene (NTces) To Achieve Practicable Yields With Halogenated Or Nonhalogenated Copper Precursors. Hammett Plots Indicate That The Competitive Amination Of Para-Substituted Ethylbenzenes Enabled By [(TMG3trphen-Sb)Cu3(ฮ-Cl)3] Involves Stepwise C-H Functionalization
A New Proper Orthogonal Decomposition Method with Second Difference Quotients for the Wave Equation
Recently, researchers have investigated the relationship between proper orthogonal decomposition (POD), difference quotients (DQs), and pointwise in time error bounds for POD reduced order models of partial differential equations. In \cite {Sarahs}, a new approach to POD with DQs was developed that is more computationally efficient than the standard DQ POD approach and it also retains the guaranteed pointwise in time error bounds of the standard method. In this thesis, we extend the new DQ POD approach from \cite {Sarahs} to the case of second difference quotients (DDQs). Specifically, a new POD method utilizing DDQs and only one snapshot and one DQ is developed and used to prove ROM error bounds for the damped wave equation. This new approach eliminates data redundancy in the standard DDQ POD approach that uses all of the snapshots, DQs, and DDQs. We show that this new DDQ approach also has pointwise in time data error bounds similar to DQ POD and use it to prove pointwise and energy ROM error bounds. We provide numerical results and plots for the POD errors and ROM errors to demonstrate the theoretical results. We also explore an application of POD to simulating ROMs past the training interval for collecting the snapshot data for the standard POD approach and the DDQ POD method -- Abstract, p. ii
Ionizable Lipid Nanoparticles Fabrication for Gene Delivery
In this project ionizable lipids were analyzed for their efficacy in delivery of mRNA in multiple metastatic lung cancer cells. Different ionizable lipids with their molar ratio in making the LNPs were analyzed in order to enhance the nucleic acid delivery to cytoplasm. Phospholipids also play a role in targeting efficacy of the LNPs to the lung cells. Different combination of ionizable lipids with multiple phospholipids were studied for physical characterization and in-vitro transcription efficiency. Transcription efficiency was then quantified using flow cytometry and optimal particles for transcription were noted
Investigation of Wide Beam and Interfacial Shear Transfer in Reinforced Concrete Structures
The use of reinforced concrete (RC) allows for unique designs of structural elements and connections because of the ability to vary the geometry and reinforcement detailing with ease. However, this freedom in the design process can lead to specialized conditions that have not been extensively studied by means of experimental testing. This is especially true for components or regions of components that are subjected to high shear loads, which are susceptible to undesirable and brittle failures. While many studies have been conducted to investigate the shear behavior of RC structural members and components to determine the critical design parameters, these tests are typically modeled after basic structural geometry and loading conditions. In modern design, geometry constraints and higher demands have pushed the envelope on RC structural members and components leading to wider beam members that are supported on narrower columns as well as connections requiring direct shear transfer across an interface to meet design demands. This study employed 3D nonlinear FEA to develop analytical models to investigate the internal forces within wide RC beam members and monolithic interface connections when subjected to shear loading. The analytical models were utilized to conduct parametric studies and develop insights into the effects of these unique conditions on the shear performance. Finally, a proposed prediction model was developed to estimate the shear transfer strength along a monolithic and non-monolithic interface connection using the results of the parametric study and data from literature -- Abstract, p. ii
In-Depth Characterization of the Selective Oxidation Products of Hafnium Carbide
Materials capable of withstanding oxidative environments at temperatures \u3e2000ยฐC are necessary for hypersonic applications. Hafnium carbide (HfC) shows a combination of properties that lends itself toward these applications; however, its oxidation behavior is poorly understood. At 1300ยฐC, HfC was found to oxidize via the following mechanism: 1) Initial oxidation of both C and Hf present in the system, 2) Formation of an interconnected pore network, whose size is related to the volume of gases being generated during the oxidation process, 3) Growth of the oxide scale to become sufficiently protective, 4) Formation of an initially amorphous โHfO2Cโ at the interface between the protective scale and the parent carbide material, on the order of nanometers, 5) subsequent decomposition of โHfO2Cโ into nanocrystalline HfO2 and turbostratic C, leading to nanoscale microstructures that are responsible for the observed gas phase diffusion controlled oxidation kinetics. The oxidation of HfC at T \u3e 1800ยฐC developed oxide scales containing only HfO2; oxidation behavior of this material appeared to change between 1600ยฐC-1800ยฐC. Microstructural observations of the oxide scales formed indicated a change in oxidation regime from gas-phase-controlled to solid-state diffusion controlled. This transition was found to correlate with the max range of the thermodynamically predicted HfO2 + C interlayer, which was affected by carbon sub stoichiometry of the system. The maximum predicted HfO2 + C stability was calculated to be 2070ยฐC for highly sub stoichiometric HfC, providing a theoretical mechanism for extending gas-phase diffusion limited oxidation control to higher temperatures. Investigations of the enthalpies of formation of HfC1-x and HfN1-y showed good agreement with theoretical predictions -- Abstract, p. i
Paleoecological and Paleoclimatic Reconstructions based on Holocene Sediment Cores, Lake Izabal, Eastern Guatemala
The Maya Region in Central America is characterized by pronounced discrepancies in precipitation, resulting in high precipitation gradients that support large-scale differences in vegetation across the region. Several lake deposits and other paleoclimate archives in the region have been studied to reconstruct past climates and palaeoecological conditions. However, actual data from proxy records have not been qualitatively and quantitatively utilized to interpret the behavior of the vegetation in moister areas within the Maya Region, such as the Lake Izabal Basin (LIB). The palynomorphs from two sediment cores in the LIB provided a good opportunity to infer the patterns of past precipitation, and environmental and human controls on paleo vegetation trends in the region that can be used to test models of Central American climate variability on different timescales. The analytical results of the 4.5 m-long Punta Chapin core, dated ~1300 cal. yr. BP based on six AMS14C dates of woody fragments, revealed a highly disturbed forest vegetation in the lower part of the core (~1300 -500 cal. yr. BP). This time corresponded to an overlap of the Terminal Classic Period and the Post Classic Period of Maya Civilization and was succeeded by a stable forest vegetation from ~500 cal. yr. BP to present. The 7.6 m-long Location 5 core was dated 9500 cal. yr. BP based on the extrapolation of eleven AMS14C dates of woody debris in the core and revealed complex interactions between climate, environments, and humans, and how they affected vegetation variability through time. Modeled mean annual temperature (MAT), mean annual precipitation (MAP), and precipitation seasonality (PSE) reveal high seasonality in the region that is reflected in the vegetation trends -- Abstract, p. i
Kinetic Modeling and Simulations of Plasma-Surface-Dust Interactions for Lunar Exploration
Due to the recent relevance of NASAโs focus on lunar missions, a better understanding of the lunar plasma-surface-dust environment is vital for their success. The lunar surface, devoid of an atmosphere and a global magnetic field, is directly exposed to solar radiation and solar wind plasma. This exposure leads to the electrical charging of the lunar surface due to the bombardment of solar wind plasma and the emission/collection of photoelectrons. Therefore, this research developed accurate and efficient computational models of plasma-surface-dust interactions and extend a legacy simulation code, namely the Immersed-Finite-Element Particle-in-Cell (IFE-PIC), to a parallel version: Parallel Immersed-Finite-Element Particle-in-Cell (PIFE-PIC) for charging problems with arbitrary geometries of lunar surface and dust charging.
The PIFE-PIC simulations underwent validation through electrostatic field and plasma dynamic problems, incorporating analytical solutions for comparative analysis with numerical results. Following this, a comprehensive strong and weak scaling parallel efficiency analysis was conducted for the PIFE-PIC framework. Finally, the code package was applied to scientific and engineering applications of plasma-surface-dust interactions, specifically, for lunar craters and individual dust particles. Fully kinetic numerical simulations were conducted to investigate plasma charging at lunar craters, some of which included lunar lander modules. The charge collection over time for dust grains was explored, considering variations in size, irregularity, the number of grains in the domain, spacing between dust grains, and permittivity. The reported results contribute to addressing a fundamental question in dusty plasma: determining the net amount of charge and distribution on each individual dust grain. In these simulations, the net charge ratio (Qd / e) is on the order of approximately 104 -- Abstract, p. ii
Methodology for Parameter Determination for Simulation Software
This research aims to present a methodology for optimizing input datasets to increase the accuracy of mathematical models and accelerate their application to engineering problems. To accomplish this goal, this work focused on the application of mathematical models to metal additive manufacturing (AM), specifically the thermal history of laser directed energy deposition (DED) of aluminum alloys. The initial steps of this body of work were to develop a mathematical model that is capable of simulating the metal AM process and applying it to the laser DED of aluminum. It was validated using the well characterized material Ti-64 and shown to have an error of 3% when predicting the width of the melt track and 20%, or less than 2 resolution steps, when predicting the depth of the melt track. Upon validation, the input parameter dataset which had the most impact on the thermal history was determined using a sensitivity analysis design of experiment (DOE), these properties were the absorption of the laser at 607โฆ C and 649โฆ C, the thermal conductivity at 649โฆ C, thermal conductivity at 1281โฆ C, and the specific heat at 460โฆ C. Upon down selection of the input parameter to increase search algorithm efficiency, a Nelder-Mead search algorithm was applied to the simulation which developed an optimized input dataset. This dataset was able to increase the accuracy of the simulation from the original dataset by over 500%, increasing the accuracy from over 600% for a generic aluminum alloy to 9.1%. It was found that the values of the laser absorption at the liquidus temperature and the specific heat at 733โฆ C, for the optimized dataset were triple that of the generic dataset. Conversely, at 922โฆ C, the generic dataset was triple that of the optimized dataset values. The thermal conductivity of the optimized dataset was about double that of the generic dataset at 1491โฆ C. Lastly, the laser diameter rudely estimated via experimentation was nearly double that of the optimized input dataset. This methodology of model development, critical parameter selection, and the application of a search algorithm is applicable across mathematical models and disciplines -- Abstract, p. i
Additive Manufacturing of Steel and Aluminum Structures: Modeling and Experiments
Additive manufacturing (AM) is defined as the process of joining materials to make objects from three-dimensional model data. Complex geometries can be easily manufactured compared to conventional subtractive methods with more freedom and flexibility in the design process. As the demand for AM process increased, it has become critical to understand the process and various parameters that constitute in affecting the quality of the manufactured part. Conducting experiments can be time intensive and costly to optimize a process. Modeling can be used as an aid to optimize, examine, and predict the process outcome.
The objective of this study is (i) To develop a meso-scale model to capture the melt pool behavior in additive manufacturing of high strength steels. A meso-scale model was developed with realistic powder properties to understand the powder behavior in the L-PBF proess. The models were validated with experimental results. (ii) To develop a constitutive material model for the stainless steels to understand the plastic behavior of stainless steels manufactured through powder bed fusion process. Low-strain rate, high temperature tensile tests were carried out to calibrate the parameters of Johnson-Cook strength model. To obtain these parameters, tensile specimens were adiditvely manufactured with 304L stainless steel powder. The material model developed was used in numerical simulation of tensile tests and compared with experimental results. (iii) To evaluate the performance of modified increased surface area aluminum honeycombs that are additively manufactured and compare them with the traditional honeycombs in sandwich applications -- Abstract, p. ii
Jet-Driven Mixing Regimes Identified In The Unsteady Isothermal Filling Of Rectangular Municipal Water Storage Tanks
Poor mixing of old and new water in municipal water storage vessels is a well-documented basis for potentially harmful water quality degradation in drinking water distribution systems. This numerical study investigates the effects of inflow and operational variables on mixing in the jet-driven filling process, with a particular focus on the transition from inadequate to sufficient mixing levels. An isothermal unsteady reynolds-averaged-navier-stokes volume-of-fluid (RANS-VOF) simulation is used to model the variable-volume filling process, accounting for the moving free surface following a draw-down in the stored water volume. A low diffusivity tracer is used to mark the old-water volume, and a coefficient of variation (CoV) quantifying the departure from a uniform tracer distribution is used to monitor the time-dependent mixing. The results indicate that adequate mixing does not necessarily follow refills from common draw-down levels. Three distinct mixing regimes are identified by unique CoV transients. Introducing consideration of the mean-flow kinetic energy, the observed mixing behaviors are readily explained by the jet inlet power and the distribution of the mean-flow kinetic energy in the tank. Extending the simulations to periods after cessation of the inflow and to partial refills, the role of residual mean-flow kinetic energy is further highlighted, especially its limited vertical reach. For cases in which a sufficiently mixed condition is achieved, the time-to-mix results are well described by a mixing-time correlation closely matching previously published results