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Beam Hardening and Scatter Artifact with Metal Objects Inside and Outside the Field of View in CBCT Imaging
No full textIntroduction: This study compares the objective and subjective appearance of artifacts produced by metal objects inside and outside the limited field of view (FOV) of a common region of interest (ROI).
Methods: Metal objects (titanium rods, zirconium rods, zirconium crucibles) were positioned in the human cadaver���s left maxilla and imaged using Accuitomo 170 CBCT with limited FOV. Sixteen scans (7 with metal inside the FOV, 7 with metal outside the FOV, and two controls) were obtained. The artifacts were objectively evaluated by calculating the standard deviation (SD) of grayscale values using ImageJ software. For the subjective test, two observers rated paired images for beam hardening/scatter artifacts.
Results: The Wilcoxon signed rank test showed no difference in the SD of grayscale values with the metal objects inside or outside the FOV (p=.2882). However, a subjective comparison of the two image groups (metal objects inside and outside FOV) showed subtle differences in beam hardening intensity in the region immediately adjacent to the metal objects. The SD of grayscale values for slices at the level of metal objects were higher than those apical to the level of metal objects (p<0.001). Conclusion: Strategic repositioning of a limited FOV CBCT to avoid metal objects did not significantly reduce the image noise. However, it reduced the beam hardening artifact on the area of the image immediately adjacent to the metal object. Additionally, selectively tilting the patient���s chin to keep metal objects in a different horizontal plane from ROI may reduce artifact appearance
Sustainable Plastic Waste Recycling: Economics and Circularity Metrics
No full textOver the past few decades, the surge in plastic waste has created an urgent need for sustainable recycling methods to align with the Circular Economy (CE) goals. Process systems engineering (PSE) models have emerged as invaluable tools in plastic waste recycling, facilitating sustainability-driven problem-solving, optimizing process frameworks, and guiding the journey toward environmentally conscious circular solutions. This work proposes a robust mathematical model to optimize different recycling technologies, including pyrolysis, gasification, mechanical recycling, and incineration, striking a balance between economic feasibility and contribution to circular economy objectives. The model recognizes the potential of chemical recycling derivatives as versatile raw materials for various applications, including methanol synthesis, ammonia synthesis, hydrogen production, and more. It reveals the possibility of plastic waste yielding energy and valuable products through open- and closed-loop recycling pathways. A novel degree of circularity metric (DOCI) is enlisted to assess these pathways' contributions to the CE critically. It integrates various vital metrics, ensuring a holistic evaluation of each recycling route, encompassing material utilization, energy demand, water usage, waste generation, carbon footprint, economic viability, co-product utilization, recyclability, quality of the product, and technology maturity. An illustrative case study involving 20 scenarios for recycling plastic waste was evaluated and analyzed against incineration as a base case. The optimization results reveal that pyrolysis refinery technology offers promising avenues for producing sustainable fuels and olefins by tripling the base case profitability and more than 25% improvement in the total degree of circularity. Moreover, seeking the maximum possible circularity can be achieved by combining methanol synthesis and the pyrolysis refinery. This will provide an overall net profit of $29 M USD/y and a 44% enhancement of the DOCI of the base case. The flexible weight allocation for DOCI individual indicators in the optimization process emphasizes the significance of tailored solutions aligned with system-specific needs. Comparisons between plastic waste and conventional feedstocks are carried out, unveiling a product-dependent cost-effectiveness landscape. Capacity-level sensitivity analysis reveals that the optimal solutions consistently outperform the base case regarding circularity and profitability
Analyzing the Effects of Groundwater Flow Rates on the Recovery Efficiency of Aquifer Thermal Energy Storage Systems Using Numerical Modelling
No full textThis study looks at the effects of groundwater flow velocity on the recovery efficiency of Aquifer Thermal Energy Storage (ATES) systems and how modifying the pumping rate and storage time can optimize the efficiency of an ATES system located in an aquifer with low to high regional flow rates. By examining the processes that control the efficiency of these energy storage systems, we hope to improve their effectiveness and contribute to their use as an energy conservation technology.
The ATES investigation was done by applying principles of heat and solute transport to a numerical model that represents a low-temperature doublet ATES system installed in a shallow confined aquifer. The finite difference method modeling suite MODFLOW was used as the primary modeling software, with MT3DMS serving as the solute transport engine. The model includes six regional groundwater flow rates ranging from 0-50 m/yr, two pumping regimes of 200-400 m3 /d (injection and extraction), and two storage times of 0-3 months. The ATES wells operated on annual cycles, with injection temperatures ranging from 5-30��C.
We found that groundwater velocity is a primary control in the recovery efficiency of ATES systems, with an average drop of 27% from no groundwater flow to 50 m/yr. Additionally, we found that at groundwater flow velocities higher than 30 m/yr, the injection rate is the most important secondary parameter, with lower pumping and injection rates associated with lower recovery efficiencies. Inversely, at groundwater flow velocities lower than 20 m/yr, storage time is the most important secondary parameter, with longer storage times associated with lower recovery efficiencies
Market and Emissions Impact of All-Electric Aircraft
No full textAviation sector greenhouse gas (GHG) emissions are projected to grow nearly 50% by 2050, motivating exploration and future adoption of reduced-emissions aircraft. While all-electric aircraft (AEA) generate effectively zero in-flight GHG emissions, their prospect for commercial implementation faces critical challenges: most notably the comparatively poor specific energy of batteries relative to aviation fuel. Unanswered questions exist regarding the prospective market and emissions impact of future AEA. This dissertation addresses these knowledge gaps, building on detailed AEA designs available in the literature to quantify AEA market impact and emissions reduction potential across thousands of varying model inputs, market bases, emissions scenarios, and timeframes. This work compares the energy consumption and emissions of conventional aircraft and AEA for every domestic commercial flight in the United States ��� nearly 9.2 million flights in total ��� determining feasibility of electrification, energy requirements, and greenhouse gas emissions for each route and providing novel quantitative estimates of potential AEA impact in the United States.
This dissertation demonstrates clear, albeit conditional, pathways for AEA to reduce aviation sector emissions. Modern-day lithium-ion batteries have insufficient energy for use in the aviation sector: AEA potential hinges on development of batteries with a specific energy three to four times greater than modern batteries. Unlike hydrocarbon-powered aircraft, the emissions footprint for AEA varies by point-of-departure based on power sector emissions generated during battery charging. Assuming historic trends in power sector emissions persist, AEA offer regional potential in the Pacific Northwest, California, and the East Coast, but would have limited national impact reducing aviation sector emissions: at maximum market penetration 1.74% to 7.95% depending on emissions timeframe for a 1000 Wh/kg onboard battery. Achieving greater emissions reduction requires transition to reduced-emissions power generation. Assuming net-zero power sector emissions, AEA could reduce total domestic aviation sector emissions by more than 27% at maximum market penetration while capturing the majority of the aviation market in terms of total flights and passenger count but would require roughly 2% of total US electricity generation (96.6 TWh). These results are highly sensitive to inherent uncertainty in the radiative forcing of non-CO��� emissions and vary by emissions model and timeframe
Environmental Impacts on Precipitation-Anvil Relationships
No full textTropical anvil cloud area response to the environmental effects of increased greenhouse gas emission is expected to be a negative cloud feedback for regulating climate sensitivity, although the magnitude of the effect is highly uncertain. This feedback is hypothesized to be caused by tropical deep convection acting as an iris in which anvil cloud coverage and properties are altered allowing more longwave radiation to escape. Recent studies hypothesize that a temperature dependence of convective aggregation could act as a potential mechanism to increase precipitation efficiency at the expense of anvil area. In this study, a precipitating, deep convection cloud object database is created using Tropical Rainfall Measuring Mission satellite observations from 2003-2014 to assess foundational relationships between the environment and precipitation, anvil cloud, and convective aggregation.
Analysis of the largest and strongest storms that contribute the most to tropical anvil cloud area and precipitation shows that precipitation-anvil relationships are more sensitive to changes in moisture rather than temperature, primarily due to greater sensitivity of convective processes to mid-level moisture. Our proxy for convective aggregation, the number of heavy rain cores in the cloud, had the strongest correlation with mid-level moisture increases which was coupled with greater precipitation increases relative to anvil cloud area. As moisture increases, the fractional contribution of different cloud components in the cloud objects shift, with more cold convection area and a reduction in the fraction of thin anvil area. On a system scale, this analysis is consistent with the mechanism that suggests organization and aggregation of convection results in greater precipitation per unit area of anvil cloud
Accelerating Finite Element Analysis Using a Multi-Fidelity Computational Scheme for Nuclear Applications
No full textNext-generation microreactors are currently being designed to be operated terrestrial and ex-traterrestrial for remote surface power production. These systems will provide an alternative source of carbon-free energy that is versatile and can be utilized for various applications. This recent de-sire to design and build next-generation nuclear systems requires high-fidelity analysis to ensure the proposed design can operate safely and as intended. Traditionally, this can be achieved by obtaining a combination of experimental and numerical results, however it has become difficult and expensive to perform integral experiments. Therefore, high-fidelity numerical results have become heavily relied upon to provide the required analysis, specifically finite-element based codes. This reliance on numerical codes has presented its own set of issues as it can take millions of CPU hours to gather the required results for a given design. Therefore, a novel computational scheme is pro-posed to accelerate transient finite element analysis of these next-generation nuclear systems. A discrepancy function between a low and high-fidelity model is approximated and used to actively correct the low-fidelity solution. By exploiting the computational cheap low-fidelity solution and a few snapshots in time of the high-fidelity solution, an approximated discrepancy function can be found to correct the low-fidelity model. This approach aims to produce a solution that is close to the full-order high-fidelity model while requiring a smaller computational cost. The idea was decided to be implemented to work alongside the Abaqus finite element software, and utilized to model a series of transient events for two conceptual reactor designs
Synthesis and Evaluation of Tribological Performance of Mxenes
No full textThis work addresses the challenges associated with the synthesis of MXene (acid etching) using an alternative method of molten salt etching and alteration of interfacial properties. This thesis is part of a thrust to develop acid free synthesis of MXenes at an industrial scale.
The initial part of the thesis is focused on the acid-free synthesis of MXenes via molten salt etching. Despite numerous prior reports of molten salt etching of MAX phases, few of these reports achieved water-dispersible MXene nanosheets and none for Nb-based MXenes. Here, we demonstrate the synthesis and aqueous dispersibility of Nb2CTz nanosheets via molten salt etching and utilizing a KOH wash to add hydroxyl surface groups. However, little is known about the oxidation of molten salt-etched MXenes compared to acid-etched MXenes. This work has indicated the slower oxidation behavior for MXenes etched by molten salts, which may be due to the decreased amount of oxygen-containing terminal groups.
A significant portion of my thesis is focused on utilizing the MXene (acid etched and salt etched) for tribological applications as liquid or solid lubricants. Owing to the high thermal conductivity, electrical conductivity, and mechanical strength of Ti3C2Tz nanosheets, they seem to be a promising candidate as lubricant additives. In this work, we evaluate the performance of Ti3C2Tz as an additive to enhance the heat transfer, rheological properties, and tribological performance of oils. The improved properties (Thermal conductivity) and reduced fluidic drag in viscosity and friction lead to potential applications in (electrical) vehicles that will help attain improved fuel economy.
Although surface terminations (such as ���O, ���Cl, ���F, and ���OH) on MXene nanosheets strongly influence their functional properties, synthesis of MXenes with desired types and distribution of those terminations is still challenging. In my thesis, we demonstrated that thermal annealing helps remove much of the terminal groups of molten salt-etched multilayered (ML) Ti3C2Tz. In this work, the chloride terminations of molten salt-etched ML-Ti3C2Tz were removed via thermal annealing. This thermal annealing created some bare sites of high surface energy and reactivity that are available for further functionalization of Ti3C2Tz. Here, the annealed ML-Ti3C2Tz was re-functionalized by ���OH groups and 3-aminopropyl triethoxysilane (APTES)z, which were evaluated as a solid lubricant, exhibiting ���70.1 and 66.7% reduction in friction compared to a steel substrate, respectively. This enhanced performance is attributed to the improved interaction or adhesion of functionalized ML-Ti3C2Tz with the substrate material. This approach allows for the effective surface modification of MXenes and control of their functional properties.
The ability to control the d spacing of MXene has proved beneficial for energy storage applications such as batteries and supercapacitors, but no one has utilized this control of interlayer spacing for lubrication. In this work, we control the interlayer spacing between the ML-Ti3C2Tz MXene via chemical intercalation. In order to alter the d-spacing, we investigated several different-sized intercalating agents. The increase in the d-spacing of ML-Ti3C2TZ MXene resulted in a drop in electrical conductivity and friction coefficient. Specifically, the enlarged interlayer gap reduced electrical conductivity in the vacuum-filtered ML-Ti3C2Tz MXene films due to increased internal resistance. Additionally, the increased d-spacing or interlayer spacing of ML-Ti3C2Tz resulted in a reduction of the coefficient of friction. This decrease is attributed to the facilitated sliding of individual ML-Ti3C2Tz layers under applied shear forces or load, resulting from the weakened van der Waals interactions due to the increased interlayer spacing
John Bickham field notebook: AK16501-AK17000.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for AK17001-AK17500 corresponding to unique identifiers of specimens/samples examined for biological research. Specimens are primarily housed at Texas A&M University; Biodiverstiy Research and Teaching Collection
Structural Analysis of Irregular Cracking in Continuously Reinforced Concrete Pavements
No full textThis research study explores the analysis of irregular cracking in continuously reinforced concrete pavements (CRC) using a synergized approach of analytical and numerical methods. A Python script was developed to execute linearized finite difference analysis, assessing temperature and moisture profiles to compute environmental stresses, including thermal and shrinkage effects. This script integrates these stresses with user inputs to run finite element analysis using the ABAQUS solver. Concurrently, the study provides a revision of the AASHTO crack spacing formula presented in the Mechanistic-Empirical Pavement Design Guide (MEPDG) for CRC pavements. The modified formula addresses the limitations of the previous version, providing insight into the depth of crack initiation. The study uncovers several key insights into early-age cracking in continuously reinforced concrete pavements including -but not limited to- variations in temperature and moisture profiles across different locations and seasons that significantly impact the cracking mechanism. Longitudinal steel cover is found to be a critical factor, with smaller cover increasing the likelihood of top-down. The study also reveals that while active cracking control is effective in determining crack locations, its efficiency is compromised when the bonding to the underlying layer is weak. Ultimately, the high bonding strength between PCC slabs and the underlying layer not only increases the possibility of bottom-up cracking but also decreases crack spacing
High-Throughput Oxidation Prediction Framework and Assessment of Refractory High-Entropy Alloys and MAX Phases
No full textAs a mode of the design process, compensating for failure is every bit as important the solution itself. Regardless of our best and most innovative efforts, devices and systems breakdown and wear out. In this work, we will examine two regimes of advanced complex alloys, MAX phases and High-entropy alloys, and make predictions on the outcomes of oxidation decomposition. To meet this goal we devise a High-throughput Finite Temperature Phase-prediction framework for simulating oxidation environments for arbitrary metallic alloys. This end-to-end framework projects ground state alloy information into the finite temperature regime with the machine-learning fitted Bartel Model. Using a least-squares algorithm, we take our studied material and the possible secondary phases to minimize the total energy of the system following semi-grand ensemble constraints at rising temperatures. By incriminating allowable oxygen, we then get a map of rapidly determined material decomposition. As an application of design in the High-entropy alloy (HEA) space, or more specifically Refractory HEA space, we sweep the combinatorial alloys regime for MoWTaTiZr materials for favorable alloy candidates for oxidation resistance. From 10%-%30 variations of constituent element concentrations, we generate 51 unique BCC via Monte Carlo Special Quasirandom Structure (MCSQS) algorithm. Applying the framework and appending an innovative metric, area-under-the-curve2 (AUC2), presented in this work, We analyzed and rank ordered the structures using a pareto front method measuring survivability of the RHEA and it���s secondary phases. Oxidation Experiments were conducted at 1373K on four samples, measuring thickness scales and mass change. Finally, and a Pillings-Bedforth ratio based "lack of monotonicity" metric we utilized to make a final design determination. We predict and experimentally confirm that HEAs composition Mo10T a30T i30W10Zr20 is the most favorable alloy. We then use this same framework as an investigation tool for previously performed Oxidation Wedge experiments for T2AlC. We do confirm a substantial aligning of oxidation decomposition and evolution. Additionally we extend this analysis for 30 211-structured MAX phases whose components are governed by the formula Mn+1AXn, where "M" is an early transition metal, "A" is an A block element, "X" is Carbon or Nitrogen and n=1,2,3. We focus on discussions of Cr2AlC, Ti2AlC, and Ti2SiC. We thus conclude an effective low cost screening process for favorable MAX phases