Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item ELECTRIFIED HIGH-TEMPERATURE MANUFACTURING AND APPLICATIONS IN ENVIRONMENTAL SCIENCE(2023) Li, Shuke; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High temperature processes hold great potential for material and chemical manufacturing.On the one hand, high temperature can help overcome energy barriers and thus effectively convert precursors to desired products. On the other hand, high temperature can also boost the reaction rate and improve synthesis efficiency. Recent development of electrified high temperature technologies by our group further revealed the important role played by non-equilibrium conditions on nanomaterial and chemical syntheses. For example, Joule-heating of carbon-based materials through a programmable electrical signal can offer spatial and temporal temperature profiles, which can be used to manipulate the chemical reaction pathways. For another example, tunable heating duration and quenching rates can be used to achieve a range of compositions and structures of nanoparticles. In this dissertation, two specific applications of the electrified high temperature technology will be explored, including: (1) Thermal shock synthesis of multielemental nanoparticles as selective and stable catalysts; and (2) Efficient biomass upgrading via pulsed electrical heating. Supported nanoparticle (NP) catalysts are widely used for various reactions. However, it remains challenging to synthesize high quality NPs with accurate morphologically and structure control. In this part of the research, NP catalysts with morphology or structural design were prepared by high temperature thermal shock methods. Ultra-small and high-loading carbon supported Pt3Ni NPs: Strong electrostatic effect was introduced between metal salts and carbon particles that can largely improve anchoring and dispersion of the precursors, thereby achieving high NP loading (40 wt%) as well as small NP size and good distribution (1.66 ± 0.56 nm). This method is not only limited to bimetallic NPs synthesis or NPs on carbon black but can be extended to a range of NP compositions on various substrate materials, thus providing a general strategy for developing ultrafine and high-loading NPs as electrocatalysts for various reactions. Sustainable aviation fuels (SAFs) are essential to meet future air travel demand while reducing the carbon footprint. Among many potential feedstocks to produce SAFs, lignin stands out as it is an abundant and renewable aromatic biopolymer that is usually treated as a waste material from the paper industry. However, converting lignin to SAFs by conventional thermochemical processes has been challenging due to poor control on the reaction pathway which leads to undesired product distribution. In this study, a programmed electrified heating method was designed and used to break down large lignin molecule to small aromatic molecules with targeted product distribution. A controlled heating step offers sufficient energy input to break down lignin molecules to smaller fragments without excessive secondary reactions toward undesired species such as coke. The lignin thermal decomposition products were evaluated as potential precursor for SAFs generation. This process can be further extended to process other biomass materials such as algae and sawdust to value-added chemicals.Item MODELING AND SIMULATION OF A SEMICONDUCTOR MANUFACTURING FAB FOR CYCLE TIME ANALYSIS(2018) Shinde, Aditya Ramaji; Fu, Michael; Systems Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The goal of the thesis is to conduct a study of the effects of scheduling policies and machine failures on the manufacturing cycle time of the Integrated Circuit (IC) manufacturing process for two processor chips, namely Skylake and Kabylake, manufactured by Intel. The fab simulation model was developed as First in First Out (FIFO), Shortest Processing Time (SPT), Priority based (PB), and Failure FIFO (machine failures) model, and the average cycle times and queue waiting times under the four scheduling policy models were compared for both the Skylake and Kabylake wafers. The study revealed that scheduling policies SPT and PB increased the average cycle time for Skylake wafers while decreasing the average cycle time for the Kabylake wafers, when compared to the base FIFO model. Machine failures increased the average cycle time for both types of wafers.Item Optimizing Mass Customization Through Interaction Variability and Manufacturing Trade-offs(2017) Cage, Kailyn; Vaughn-Cooke, Monifa; Fuge, Mark D; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Design methods that consider the complete physical system (human interfaces and functional capacities of human interfaces) and incremental distinctions in humans are not widely applied. Human beings vary from a cognitive and physical standpoint. Manufacturing approaches have attempted to implement mass customization to provide end users with personalized products. However, these approaches are limited since (1) mass customization is orthogonal to human variability and (2) manufacturing costs are increased, through additional time and parts, required when mass-producing customized products. This research facilitates the integration of traditional engineering performance metrics and biomechanics creating manufacturable innovations in customized design that target population accommodation. The present method captures (1) human and product interface interactions, (2) interaction accommodation, (3) the impact of interaction accommodation on engineering performance metrics (thermal, structural, fluid, reliability, etc.), and (4) number of products required to accommodate the population. Engineering design techniques provide a structured method for reducing product and performance metrics which provide the foundational framework for the optimization model(s) integrating this method. Optimization enables optimal performance metrics constrained by population accommodation, producing the product metrics and the number of products required to accommodate the population. This work is a novel approach for addressing complex questions for interaction variability in mass production targeting population accommodation while maintaining product performance, which facilitate addressing larger problems of mass customization in mass production.Item Design of An Automated Assembly Line for Manufacturing Visual Tension Indicating Fasteners(2012) Eslami, Babak; Thamire, Chandrasekhar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Threaded fasteners play a major role in mechanical assemblies to clamp components or flanges. While bolted joints have been in use for many centuries and are simple to design and use, they are not foolproof; it is often difficult to achieve the required clamping force accurately by applying the designer-prescribed tightening torque, determined assuming ideal conditions of the contacting surfaces. Therefore, a concept that can directly measure tension on bolted joints is necessary. In this work, the concept of visual tension indicating fasteners is introduced and explained. After testing the feasibility of the concept, an automated assembly line is designed and fabricated in order to produce these fasteners with a more reliable manufacturing process.Item MANUFACTURING SECTOR PRODUCTIVITY IN INDIA: ALL INDIA TRENDS, REGIONAL PATTERNS, AND NETWORK EXTERNALITIES FROM INFRASTRUCTURE ON REGIONAL GROWTH(2010) Mohommad, Adil; Hulten, Charles R; Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation I examine sources of growth in the formal manufacturing sector in India, from 1970 to 2003. I consider both all-India trends and state-level trends in the growth of resource efficiency, measured by TFP, and the relative contribution of TFP growth to output growth in manufacturing, as compared to capital accumulation. At the state level, I also examine the relationship between per-capita income and trends in output per worker and TFP in the manufacturing sector. Finally, in a spatial econometric framework, I test for the presence and magnitude of network spillovers from infrastructure, including national and state highways, and electricity generation capacity, on manufacturing TFP levels across states. My work contributes to an on-going debate on the response of manufacturing sector TFP to the implementation of economic reforms in India, in the 1980s and 1990s. At the regional level, this dissertation addresses not only the literature on the causes behind rising income inequality across states, but also on the role of infrastructure on regional growth, restricting attention to the manufacturing sector. The results of this dissertation show that at the all-India level and at the state level, manufacturing sector TFP growth accelerated in India during periods of economic reform. The contribution of TFP growth to output growth increased in the 1990s relative to earlier periods, and exceeded the contribution of capital accumulation. At the state level, I find evidence of convergence in growth rates of output per worker and TFP in manufacturing. I do not find evidence of a significant correlation between output per worker in manufacturing and state per-capita incomes. Given the relatively small share of the manufacturing sector in state GDP on average, these results imply that the source of rising income inequalities across states may not be manufacturing. Finally, I find some evidence to suggest that there exist positive network spillovers from physical infrastructure on manufacturing sector TFP. The results suggest that doubling the stock of national and state highways, and electricity generation capacity can lead to a nine percent increase in manufacturing sector output.Item The Impact of Globalization on Inventory and Financial Performance: A Firm-Level and Industry-Level Analysis(2009) Han, Chaodong; Dresner, Martin E; Dong, Yan; Business and Management: Logistics, Business & Public Policy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation investigates how globalization affects inventory and financial performance from both firm and industry perspectives. Drawing upon elements from classic inventory models, transaction costs, geographic economics, and international business and strategy literatures, this dissertation aims to contribute to the construction of a theory of global supply chain management through an empirical testing of hypotheses on the effects of global sourcing, exports and manufacturing offshoring (i.e., foreign subsidiaries) on inventory performance and financial performance, using data from multinational firms and U.S. manufacturing industries. Motivated by the lack of empirical research on inventory management in a global context, and an uncertain relationship between globalization and financial performance reported in the international business and strategy literature, the first essay examines how globalization affects firm financial performance directly and indirectly through inventory management. Globalization is further examined by a two-dimensional measure: global intensity and extensity. Due to increased uncertainties associated with global supply chains, globalization may significantly increase firm inventory levels. Even though manufacturing offshoring may benefit multinational firms through economies of scale and geographic diversification, escalating transaction costs and shrinking arbitrage opportunities may overwhelm benefits and lead to reduced financial performance. This direct-indirect effect model is tested using a large panel dataset of thousands of multinational firms over 1987-2007, collected from the COMPUSTAT global and segment databases. Essay 1 contributes to the supply chain management literature by providing a two-dimensional measure of globalization: foreign market penetration (depth) and geographic expansion (breadth), and may enhance our understanding of global supply chains. The second essay analyzes the impact of global inbound and outbound supply chains on inventory performance within the U.S. economy. This research argues that global activity (i.e., global sourcing and exports) has offsetting effects on domestic inventory levels: an increasing impact due to risk considerations and a decreasing impact due to cost pressure from rising inventory costs. According to location theory, rooted in geographic economics, and "new trade theory" on intra-firm trade, firms may be able to efficiently allocate inventories to low cost regions along their global supply chains. To the extent that allocative efficiency may only be realized once a certain level of global activity is reached, it is hypothesized that the impact of international trade on domestic inventory is inverted-U shaped. i.e., as globalization increases, inventory levels first increase due to the longer and more complex supply chains, then decrease as firms determine how to more efficiently allocate their inventory across borders. The hypotheses are tested using inventories at all three stages (raw materials, finished goods and work-in-process inventory) and industry operating data from U.S. manufacturers over the period 1997-2005. Regression results indicate a strong invert-U shaped relationships existing between import intensity (measured by imported raw materials as a percentage of industry total cost of materials) and raw materials inventory in days of supply, and between export intensity (measured by exported finished goods as a percentage of total value of industry shipments) and finished goods inventory in days of supply. Essay 2 makes two contributions: theoretically, it is the first effort to connect international trade with inventory performance; empirically, results based on all U.S. manufacturers over a recent nine-year period may provide a benchmark for management when designing global inventory strategy. In summary, this dissertation comprehensively investigates the impact of global supply chains on inventory performance and financial performance in the context of multinational firms and U.S. domestic manufacturers and hence is expected to enhance our understanding of global supply chain management theory and practices.