Browsing by Subject "Interface"
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Item Computational, theoretical investigation of materials for a sustainable energy future(2016-08) Stauffer, Shannon Kaylie; Henkelman, Graeme; Mullins, Charles B; Crooks, Richard; Hwang, Gyeong; Milliron, DeliaOver the past several decades there has been significant progress in electronic structure theory, statistical sampling algorithms and computational resources which can be leveraged to calculate fundamental properties of materials and estimate rates of relevant chemical reactions. In the following dissertation, I use computational methods to address the materials problem of a sustainable energy future. Energy storage technologies have played a vital role in the mobile-technology revolution and the transition to utilize more sustainable energy sources; however improvements to the energy density, charge/discharge rate, and safety of rechargeable batteries are needed to realize the ambitious goals of fully electric vehicles and on-grid storage in areas with intermittent, renewable power sources. Li-ion batteries, in general, have a potential to fulfill these demands. In the following work, a new, high energy density electrode material with little capacity loss is considered. Additionally, the complex interaction between an electrode/electrolyte model system is considered in a potential dependent computational framework. Having a sustainable energy future also means utilizing energy-efficient processing in industrial scale applications. Separation processes use roughly 12% of all energy consumed in the United States due to energy-intensive thermal separation techniques. A final study looks at an alloy catalysts for the separation of ethylene from ethane/ethylene mixtures. A unique selectivity property was discovered that may help design catalysts to replace thermal separation of gases.Item The Design and Control of Stability and Magnetic Properties of Imaging Nanoparticles(2012-12) Yoon, Ki Youl; Johnston, Keith P., 1955-; Bryant, Steven L; Milner, Thomas E; Huh, Chun; Ruoff, Rodney S; Ferreira, Paulo JThere is significant interest in applying nanoparticle (NP) science to subsurface reservoirs to facilitate oil and gas recovery, image subsurface reservoirs, aid sequestration of CO2 and benefit environmental remediation. Imaging nanoparticles have been designed with long-term dispersion stability in brine and minimal retention in reservoir rock and with preferential adsorption at oil-water interfaces. Polymer-stabilized nanoparticles provide sufficient electrostatic repulsion for high colloidal stability, as characterized by the zeta potential. The small size of the clusters, superparamagnetic properties, and high salt tolerance are highly beneficial in various applications including magnetomotive and electromagnetic imaging and mapping of petroleum reservoirs. Superparamagnetic nanoclusters may be used in imaging in biomedicine and in mapping of petroleum reservoirs, by generating either ultrasonic or acoustic signals with oscillating magnetic motion. For a given magnetization per weight of iron oxide, nanoclusters with sub ~100 nm diameters experience a much larger magnetic force than that of the primary sub- 10 nm primary particles. Aqueous dispersions of 0.1-0.2 wt% superparamagnetic iron oxide nanoclusters were stabilized with citric acid, poly(acrylic acid) (PAA), or poly(styrene sulfonate-alt-maleic acid) (PSS-alt-MA) on the particle surface, with a high loading of ~90% iron oxide. For nanoclusters with only 12% (w/w) PSS-alt-MA electrosteric stabilization was sufficient even in 8 wt% NaCl. Both PAA and PSS-alt-MA were used to stabilize nanoclusters with controlled size during synthesis in aqueous media. To obtain a permanent coating on the surface of clusters cross-linking of the polymer for different cross-linking densities was applied. In this general and highly flexible approach, iron oxide nanoparticles may be formed with an adsorbed polymer stabilizer, which is then permanently bound to the surface via cross-linking. To investigate interfacial activity of nanoparticles, oil-in-water emulsions were stabilized with iron oxide nanoclusters or graphene oxide platelets. In each case, the stabilization was achieved by designing the hydrophilic/hydrophobic nature of surface coating. For oil/water emulsions, the droplet size was as low as ~1 micron diameter, and strongly shear-thinning rheology was observed. A series of sub-100 nm superparamagnetic iron oxide nanoparticles with amphiphilic poly(acrylic acid-b-butylacrylate), (PAA-b-PBA) copolymer shells was synthesized to investigate the effect of the polymer structure on the interfacial tension for nanoparticles adsorbed at the dodecane-water interface. Large reductions in interfacial tension of up to 27.6 mN/m were obtained for a 0.27 wt% nanoparticle concentration indicating significant nanoparticle adsorption and interaction with the oil and water molecules at the interface. The adsorption energy of the polymer-coated nanoparticles at the dodecane/water interface was determined from the interfacial tension and nanoparticle radius, and analyzed in terms of the structure of the polymer stabilizer. Furthermore, oil-in-water emulsions stabilized with graphene oxide nanoplatelets were found to remain stable for several months even at high salinity (up to 5 wt% NaCl, for pH = 2 to 10). The droplet sizes were as small as ~1 μm with a low nanoplatelet concentration of 0.2 wt%.Item Development of an ArcGIS interface and design of a geodatabase for the soil and water assessment tool(Texas A&M University, 2004-09-30) Valenzuela Zapata, Milver AlfredoThis project presents the development and design of a comprehensive interface coupled with a geodatabase (ArcGISwat 2003), for the Soil and Water Assessment Tool (SWAT). SWAT is a hydrologically distributed, lumped parameter model that runs on a continuous time step. The quantity and extensive detail of the spatial and hydrologic data, involved in the input and output, both make SWAT highly complex. A new interface, that will manage the input/output (I/O) process, is being developed using the Geodatabase object model and concepts from hydrological data models such as ArcHydro. It also incorporates uncertainty analysis on the process of modeling. This interface aims to further direct communication and integration with other hydrologic models, consequently increasing efficiency and diminishing modeling time. A case study is presented in order to demonstrate a common watershed-modeling task, which utilizes SWAT and ArcGIS-SWAT2003.Item Experimental investigation of shear transfer between concrete interfaces(2014-12) Massey, Joshua Brice; Bayrak, Oguzhan, 1969-; Jirsa, James OThis experimental program was focused on the effect of surface geometry (shear keys) on the transmission of shear forces between concrete cast against a hardened concrete interface. This research was part of a larger study at The University of Texas at Austin focused on several aspects of spliced precast concrete girder technology, particularly those concerning the interface between precast girders and cast-in-place splices. 14 push-through type specimens were tested with varying surface geometries, interface reinforcement ratios, and levels of prestress normal to the interface. The surface types considered included smooth, single shear keys, multiple shear keys, saw teeth of multiple depths and a monolithic specimen for comparison. The principle findings were that surfaces with properly detailed indentations could transfer significantly higher shear forces before slip occurred than smooth surfaces, and that shear keys generally displaced better performance than saw-teeth. Forces from prestress and yielding of reinforcement crossing the interface during failure were found to contribute to the strength in effectively the same manner. In addition, the shear friction based provisions of ACI 318-11, AASTHO LRFD 2012, and Eurocode 2 were found to provide satisfactory predictions of the ultimate strength of such surfaces with reinforcement ratios less than 0.75 %.Item Fracture and delamination of elastic thin films on compliant substrates : modeling and simulations(2011-08) Mei, Haixia; Huang, Rui, doctor of civil and environmental engineering; Liechti, Kenneth M.; Landis, Chad M.; Mear, Mark E.; Ho, Paul S.Different fracture modes have been observed in thin film structures. One common approach used in fracture analysis is based on the principle of linear elastic fracture mechanics (LEFM), which assumes pre-existing cracks and treats the materials as linear elastic except for the damage zone around the crack tip. Alternatively, a nonlinear cohesive zone model (CZM) can be used to simulate both nucleation and growth of cracks. In this dissertation, the approaches of LEFM and CZM are employed to study fracture and delamination of elastic thin films on compliant substrates under various loading conditions. First, compression-induced buckling of elastic thin films on elastic compliant substrates is studied by analytical and numerical methods. The critical condition for onset of buckling instability without and with a pre-existing delamination crack is predicted. By comparing the critical strains, a map for the initial buckling modes is constructed with respect to the film/substrate stiffness ratio and the interfacial defect size. For an elastic film on a highly compliant substrate, nonlinear post-buckling analysis is conducted to simulate concomitant wrinkling and buckle-delamination, with a long-range interaction between the two buckling modes through the compliant substrate. By using a layer of cohesive elements for the interface, progressive co-evolution of wrinkling and delamination is simulated. In particular, the effects of interfacial properties (strength and toughness) on the initiation and propagation of wrinkle-induced interfacial delamination are examined. Next, using a set of finite element models, the effects of interfacial delamination and substrate penetration on channel cracking of brittle thin films are analyzed. It is found that, depending on the elastic mismatch and the toughness of interface and substrate, a channel crack may grow with interfacial delamination and/or substrate cracking. By comparing the effective energy release rates, the competition between the two fracture modes is discussed. Cohesive zone modeling is then employed to simulate nucleation and growth of delamination and penetration from the root of a channel crack. By comparing the results from the approaches of LEFM and CZM, the characteristic fracture resistance from small-scale bridging to large-scale bridging is identified. Finally, to determine the nonlinear traction-separation relation for cohesive zone modeling of a bimaterial interface, a hybrid approach is developed by combining experimental measurements and finite element simulations. In particular, both analytical and numerical models for wedge-loaded double cantilever beam specimens are developed. A two-step fitting procedure is proposed to determine the interface toughness and strength based on the measurements of the steady-state crack length and the local crack opening displacements.Item A fracture mechanics approach to accelerated life testing for cathodic delamination at polymer/metal interfaces(2013-05) Mauchien, Thomas Kevin; Liechti, K. M.This work presents a fracture mechanics analysis of the cathodic delamination problem for the polyurethane/titanium and polyurea/steel interfaces. The nonlinear behavior of both polymers was investigated. The recent Marlow model was used to define the strain energy function of the polymers. Viscoelastic effects of the polyurea were also studied. The Marlow model was associated with a nine-term Prony series. This model was seen to represent experimental data relatively well for a wide range of strain rates both in tension and compression. The driving force for delamination, the strain energy release rate G, is presented for both interfaces. Cathodic delamination data for several temperatures are presented as crack growth rate as a function of crack driving force. The approach recognizes that both temperature and stress can be used as accelerated life testing parameters.Item The impact of the business-project interface on capital project performance(2013-08) Yun, Sungmin; O'Brien, William J.; Mulva, Stephen PatrickA capital project represents a significant investment by a firm to create future economic benefits. Since the global economic recession begun in 2008, corporate owners have paid increased attention to business-project interfaces with the aim of improving alignment between business strategy and capital project development. Despite its importance, the business-project interface has not been quantitatively measured and no empirical evidence exists about its effects on performance outcomes. This dissertation intends to identify and quantify the business-project interfaces in the development of a capital project in terms of personnel involvement and task interaction, and to investigate its effects on performance outcomes and the value of best practices. To achieve these objectives, a conceptual framework for assessing the involvement and interaction on business-project interfaces was developed. Based on the conceptual framework, a questionnaire including quantitative measures for the assessment of personnel involvement and task interaction was designed. Supplemental survey responses were received for several industrial capital projects that had initially provided capital project data to the CII Benchmarking & Metrics database. The effects of the business-project interface in terms of cost, schedule, change, and business performance were documented. Data analyses show that project groups with high involvement by business personnel and high interaction between business and project units tend to show remarkably improved project performance. Furthermore, this dissertation presents confirmation that projects with high involvement of business unit personnel and intensive implementation of best practices tend to show superior project performance. The primary contribution of this research is to provide a quantitative assessment tool to assess the business-project interface and to document the interface throughout project life cycle. Another contribution is empirical evidence of the benefits on project performance from implementing best practices that were supported by management.Item Modest : Modeling, Debugging, and Testing distributed programs(2016-12) Rosales, David Andrew; Garg, Vijay K. (Vijay Kumar), 1963-Modest (Modeling, Debugging, and Testing) is a graphical modeling and testing environment for simulating the execution of distributed systems. Its objective is to assist as a learning tool but more importantly to aid in the design and implementation of distributed algorithms. It builds the simulation environment which means that only the algorithm is required from the user to perform testing. Logging and message animations help understand what events have occurred. Modest has the ability to replicate real life scenarios by inflicting network latency, network failures, and server failures. With the ability to quickly customize environment configuration and options, custom algorithm simulation can be initiated in minimal amounts of time. The concept of distributed computing can be complicated and Modest helps to simplify it with a modern user interface design.Item Multimedia learning: Cognitive individual differences and display design techniques predict transfer learning with multimedia learning modules(2005-05) Stalcup, Katherine A. A.; Maki, William S.; DeLucia, Patricia R.; Reich, Darcy A.; Bleckley, M. Kathryn; Durso, Francis T.Psychologists and engineers continue to debate the efficacy of technology interfaces and merit of information display approaches. In the wake of the information explosion and rapidly progressing technology, Mayer (2001) formulated a theory that focused on human cognition, rather than technology capacity and features. Mayer and colleagues have developed a simple model, the Cognitive Theory of Multimedia Learning, suggesting that certain combinations of multimedia optimize learning, in terms of retention and transfer. The present dissertation suggests that the conclusions are premature and a much more complex set of individual differences and display design principles must be evaluated. Further, the Cognitive Theory of Multimedia Learning is vulnerable in terms of its simplistic view of information processing and working memory. For instance, when previous research tested individual difference attributes, such as spatial ability and prior knowledge, performance was evaluated only in the animation and narration condition, representing one of his three initial experimental conditions (Mayer, 2001). The present research offers a rigorous comparative analysis of the multimedia conditions. In addition, variables such as working memory, multimedia comprehension skill, and fluid intelligence are measured and isolated, so that the multimedia combination effect on transfer learning can be evaluated beyond these cognitive abilities. By measuring the effect of cognitive individual differences and display design manipulations on transfer test performance, the current research offers a broader approach to testing the impact of multimedia combinations on transfer test performance. The present research concludes that while cognitive primitives contribute to learning transfer in a multimedia lesson, display design manipulations involving text location and the absence of motion remove the effects reported in previous research. Ultimately, there is no “magic bullet” combination of multimedia (animation and narration). Rather, key design principles coupled with the influence of cognitive individual differences must be investigated further before prescriptive guidelines for educational multimedia can be proffered. Likewise, the predictive validity of cognitive primitives, such as fluid intelligence, may redirect interest back to fundamental individual differences, as indicators of learning differences with or without the effect of technology.Item A phone application to provide advanced remote control functionality to an embedded systems product(2010-08) Michel, Larry Ashley; Khurshid, Sarfraz; Julien, ChristineWith the increasing popularity of phone application development, a number of features have surfaced that enable users to utilize extended functionalities with their phone. With a single device, a user is now able to have access to the latest trends. As a result, functionalities from various products such as personal computers or GPS devices can now be accessible in one place. While this technology is evolving at a fast rate, it is the embedded technology and hardware that drive it which facilitate the innovative designs and solutions. At the other end of the spectrum of embedded systems, companies continue to maintain legacy products that use embedded chips programmed through their flash memory. With this perceived commitment to stay loyal to their older product designs, it has become rather cumbersome for such companies to stay current with the latest hardware and software trends. The result is higher costs to the customers for their high-end products. While the average user invests in newer and faster Google phones or iPhones, it is unlikely that the same can be said for commercial products such as a refrigerator or a ball machine. What if a development framework existed that allowed customers to have access to better user interfaces and functionalities over the lifetime of their product? In this Masters report, an innovative approach is discussed which demonstrates the latest mobile phone technology combined with an existing embedded device being applied to the conversion of a low-end tennis ball machine into an affordable high-end one.Item Thermomechanical and interfacial properties of monolayer graphene(2014-08) Gao, Wei, active 21st century; Huang, Rui, doctor of civil and environmental engineeringThe thermomechanical properties of monolayer graphene and the interfacial interactions between graphene and an SiO₂ substrate are investigated in this dissertation using a multiscale approach. The temperature dependent mechanical behavior of graphene with thermal fluctuations is studied by statistical mechanics analysis under harmonic approximation, which is then compared to molecular dynamics simulations. It is found that the amplitude of thermal fluctuation depends nonlinearly on the graphene size due to anharmonic interactions between bending and stretching modes, but a small positive pre-strain could suppress fluctuation amplitude considerably and results in very different scaling behavior. The thermal expansion of graphene depends on two competing effects: positive expansion due to in-plane modes and negative expansion due to out-of-plane fluctuations. The in-plane stress-strain relation of graphene becomes nonlinear even at infinitesimal strain due to the entropic contribution. Consequently, the modulus of graphene depends on strain non-monotonically, with strain stiffening followed by intrinsic softening. Moreover, it is found that the thermomechnical behavior of graphene is dependent on its interactions with environment such as supporting substrate. The interfacial interactions between graphene and SiO₂ substrate is investigated in terms of three perspectives. Firstly, the interaction mechanisms between graphene and SiO₂ substrate are studied by density functional theory (DFT). The dispersion interaction is found to be the predominant mechanism, and the interaction strength is strongly influenced by changes of SiO₂ surface structures due to surface reactions with water. The adhesion energy is reduced when the reconstructed SiO₂ surface is hydroxylated, and further reduced when covered by a monolayer of adsorbed water molecules. Next, we study the interfacial interactions between graphene and a wet substrate that is covered by a liquid-like water film. During the separation of graphene from the wet substrate, MD simulations show evolution of the water from a continuous film to discrete islands. The water bridging effects are further described by continuum models. Finally, a continuum model is developed to predict how the surface roughness may affect the adhesion between graphene membranes and their substrate.Item Web-based feedback system: the life cycle management as continuous maintenance of apartment facility information(Texas A&M University, 2006-10-30) Jeong, Jin SuThis research investigates the feasibility of web technology as a means of delivering facility information for better support of facility operations and maintenance. This study proposes a web-based feedback system as a pragmatic solution to the limitations of current facility management (FM) processes, increasing the efficiency of these processes via web technology. In practice, work orders and records are often misplaced, resulting in reduced efficiencies, redundancies, and time-consuming, costly tasks. This problem may be overcome by use of a system that stores information digitally and provides a web-based interface. The interface could allow operations personnel to create documentation, share and monitor work orders, provide feedback for service online, and facilitate communication between facility teams. The benefit for a FM department is that it can receive feedback on performance, which would improve the quality of service and build a record of practical experiences. In this research, the software was tested using two types of prototype testing: first, system testing to evaluate functionality, usability and capability; and second, a post-task questionnaire survey was conducted to test and review the concept, interface, and usability of the system. Facility Management Industry Advisor Council (FMIAC) members answered the questionnaires after using the system posted on the web. By using web-based feedback system, a facility web site can be created and maintained easily through a standard web browser. The questionnaires from the FMIAC members were analyzed to test research questions. The tests show that the software aids facilities managers in maintaining living documents of their facilities.