No description available.

The cells of 𝘊𝘶𝘤𝘶𝘳𝘣𝘪𝘵𝘢 embryos contain may protein bodies surrounded by smaller lipid vesicles. Within the protein bodies are discrete spherical bodies called globoids. Globoids are made up of phytin, and are an important store of 𝘮𝘺𝘰-inositol, phosphorus, and cations including K, Mg, Ca, Mn, Fe and Zn. During early seedling growth, the protein bodies fuse together to form aqueous vacuoles, and the globoids are degraded, their mineral nutrient stores used by the growing seedling. The changes in the element composition of globoids during early seedling growth were examined in this study and the influence of light and mineral nutrient conditions on the changes were examined. Energy dispersive X-ray analysis was used to determine the element composition of globoids from the cotyledons of 𝘊. 𝘮𝘢𝘹𝘪𝘮𝘢 and 𝘊. 𝘢𝘯𝘥𝘳𝘦𝘢𝘯𝘢 seeds and seedlings at various stages of growth. The stages selected ranged from the mature, dry seed, to an established seedling with an elongated hypocotyl and expanded cotyledons. To investigate the influence of light and mineral nutrient conditions, seedlings were grown under four different sets of growth conditions: in the dark, with deionized water; in the dark, with Hoaglands solution; in the light, with deionized water; in the light, with Hoaglands solution. During early seedling growth, the element composition of globoids changed. In both species, regardless of growth conditions, the same general trend was observed for each element: P remained relatively constant, K decreased markedly and Mg, Ca, Mn, Fe, and Zn generally increased. As the protein bodies fused and became more aqueous, it appeared that K ions came off the phytate molecule and were replaced by di-and trivalent cations with a higher affinity for phytic acid. There were species-to-species differences in globoid composition changes which could be attributed, at least in part, to differences in the Ca content of the mature, dry embryos. In 𝘊. 𝘢𝘯𝘥𝘳𝘦𝘢𝘯𝘢, which had a higher initial Ca content, there was a large increase in the Ca content of the globoids during seedling growth and no significant increase in Mn. In 𝘊. 𝘮𝘢𝘹𝘪𝘮𝘢 globoids there was only a slight increase in Ca, but there was a much larger increase in Fe, Zn and Mn than occurred in 𝘊. 𝘢𝘯𝘥𝘳𝘦𝘢𝘯𝘢. Light and dark grown seedlings exhibited distinctly different morphological features, but light conditions alone did not have a significant influence on the changes in globoid composition. In combination with mineral nutrients in the later stages of growth, the presence of light resulted in a more rapid degradation of globoids. Mineral nutrient conditions had some effect on globoid composition, affecting mostly elements which were present in large amounts. The effect of mineral nutrient conditions, and its interactions with light conditions may have been mediated through changes in the mobilization of mineral nutrients out of the cotyledons during seedling growth. There were very large (5 -7μm in diameter) globoid-like particles present in some later stage cotyledon samples of both species. There was no apparent pattern to which samples they were found in. These particles had elemental compositions which were consistent with them being composed of phytin. Such large particles had not previously been found in cucurbit tissues. / Thesis / Master of Science (MS)

In wheat grains, mineral nutrients are stored in spherical particles called globoids. Globoids are located within the protein bodies of cells from the aleurone layer, scutellum and embryonic axis of the wheat grain. Composed of phytate, globoids contain an essential source of myo-inositol, P, K, Mg, Ca, Mn, Fe and Zn which are used by the growing seedling during early seedling growth. Changes to the element composition within the globoids from the aleurone, scutellum and embryo axis, during seed set and early seedling growth were examined in two cultivars of wheat through the use of energy dispersive X-ray analysis. During seed set and early seedling growth the composition of the globoids within all tissues changed. In each of the tissues in both cultivars the P levels decreased during seed set and remained relatively constant during early seedling growth. K levels increased during seed set and decreased during early seedling growth. Mg and Ca levels generally decreased during seed set and increased during early seedling growth. Mn and Zn were detected only within globoids within the embryonic axis and no changes were noted for these two elements. Energy dispersive X-ray analysis showed that A.C. Reed and Celtic grains both followed the same general trends during seed set and seedling growth indicating that the differing protein content of the two cultivars had little effect on the timing of mineral nutrient accumulation and utilization within the globoids. Atomic absorption analysis of whole grain tissue for P, K, Mg and Ca revealed that Celtic grains had higher concentrations of P and K while being grown in identical conditions to that of A.C. Reed grains. These results indicate that mineral nutrient levels within the grain seem to be influenced by the cultivar, and possibly the protein content of the particular cultivar. / Thesis / Master of Science (MS)

No description available.

Wear and corrosion are two major threats to material integrity in multiple real-life circumstances, including oil and gas pipelines, marine and offshore infrastructures and transportations and biomedical implants. Furthermore, the synergistic effects between the two, named tribocorrosion, could cause, most of the time, severer material degradation to jeopardize materials' long-term sustainability and structural integrity. A representative case is aluminum (Al) and its alloys, which exhibit good corrosion resistance in aqueous solution due to the protection provided by the passive layer. However, these naturally formed layers are thin and delicate, leaving the materials vulnerable to simultaneous mechanical and corrosion damage, which in turn, compromise their resistance to tribocorrosion. Past research in tribocorrosion mainly relies on costly and trial-and-error experimental methods to study the materials' deformation and degradation under simultaneous wear and corrosion. In an attempt to predict tribocorrosion behavior using numerical analysis, this work developed a set of finite-element-based multiphysics models, in combination with experimental methods for parameter input and validation, focusing on different factors influencing the tribocorrosion behavior of materials. The first study developed a model with the coupling between strain and corrosion potential and investigated the effect of bulk material properties on tribocorrosion. This model was validated by existing tribocorrosion experiments of two Al-Mn alloys, to analyze the synergistic effects of mechanical and corrosion properties on the material degradation mechanisms of tribocorrosion. During consecutive passes of the counter body, significant residual stress was found to develop near the edge of the wear track, leading to highly concentrated corrosion current than elsewhere. Such non-uniform surface corrosion and stress-corrosion coupling led to variations of tribocorrosion rate over time, even though testing conditions were kept constant. Tribocorrosion rate maps were generated to predict material loss as a function of different mechanical and electrochemical properties, indicating a hard, complaint metal with high anodic Tafel slope and low exchange current density is most resistant to tribocorrosion. Secondly, the influence of microstructural design on the tribocorrosion behavior of Al-based nanostructured metallic multilayers (NMMs) was investigated computationally. Specifically, this model accounts for elastic-plastic mechanical deformation during wear and galvanic corrosion between exposed inner layers after wear. The effects of individual layer thickness (from 10 to 100 nm) and layer orientation (horizontally and vertically aligned) on the tribocorrosion behavior of Al/Cu NMMs was studied. Both factors were found to affect the subsurface stress and plastic strain distribution and localized surface corrosion kinetics, hence affecting the overall tribocorrosion rate. This model and the obtained understanding could shed light on future design and optimization strategies of NMMs against tribocorrosion. Finally, a combined experimental and computational investigation of the crystallographic effect using Al (100), (110), and (111) single crystals as model systems, to understand the effects of crystallographic orientation on the tribocorrosion kinetics by combining tribocorrosion experiments, materials characterization, and multiphysics modeling. EBSD was exploited to characterize the crystal orientation and dislocation density of the worn samples. The tribocorrosion model was built based on the results of EBSD characterization with the coupling effect of crystal orientation and corrosion. The model successfully predicted the overall tribocorrosion current of single-crystal samples, indicating the important role played by crystal orientation and dislocation density in the acceleration of corrosion. / Doctor of Philosophy / Multiple applications in batteries, aerospace, marine transportation, offshore infrastructure and biomedical implants request metal materials that are both mechanically reliable and corrosion resistant. In addition to pure mechanical wear and corrosion, the synergy of the two, which is called tribocorrosion, also poses major threat to materials' integrity and longevity. Aluminum is a widely used passive metal due to its advantage of being cheap, light-weighted and corrosion resistant, but is relatively less resistant to wear comparing to other metals. Mechanical damage could strip Al of the protection from the passive layer and also cause stress corrosion. This makes Al susceptible to tribocorrosion. Despite several previous experimental attempts to understand the mechanism of Al tribocorrosion and improve the tribocorrosion resistance of Al by alloying or structural design, there has been little quantitative model on this topic. In this dissertation, finite element (FE) multi-physics modeling was exploited to investigate the tribocorrosion phenomenon on Al systems in sea water environment. The first model was developed based on strain-electrochemistry coupling and helped study the effect of alloys' composition on the tribocorrosion resistance of the alloy. The second model studied the tribocorrosion of Al/Cu multilayers with the focus on the micro-galvanic coupling between Al and Cu layers and predicted the influence of layer thickness and orientation. The third model exploited the result of crystallographic information from EBSD characterization to study the mechanism of pure Al tribocorrosion on the crystal level. These models provide quantitative explanation to the accelerated corrosion of Al-based metals and structures, as well as guidance to future design of material with optimum wear, corrosion and tribocorrosion resistance.

Human activities associated with the injection of fluids at depth are known to trigger earthquakes. Fluid injection increases the internal pore pressure of the host rock, which in turn reduces the effective stress and frictional resistance of faults that maintain the fractured rock system in a state of mechanical equilibrium. Under certain conditions, sufficiently high pore pressure can lower this frictional resistance below a critical threshold and initiate an earthquake – the relative motion of rock on either side of the fault plane. Many of these earthquakes are small and imperceptible without the aid of specialized instruments, but some may be large enough to pose a significant risk to life and property. Several emerging technologies that have the potential to shape the future of low-carbon energy production, including carbon capture and storage and enhanced geothermal energy production, are inextricably linked to large-scale injection of fluids into the subsurface. The risk of injection-induced earthquakes is a primary concern and potential barrier to widespread adoption of these technologies. New tools are required to help operators manage these risks and meet stakeholder expectations. Current knowledge enables operators to predict the conditions that would trigger such an earthquake, but few or no tools exist to predict the severity of the earthquakes, precluding a complete description of the risk associated with operating a large-scale injection well. This dissertation details the theoretical justification and initial validation of a methodology and software to simulate the motion of an earthquake as it occurs and quantify the severity in terms that are germane to experts in earthquake science. Specifically, this work utilizes the finite element method to solve the equations of motion dictated by the three-dimensional linear elastic constitutive equation. Novel aspects of this research include the treatment of friction at the fault interface as a constraint on the motion of the system, and the numerical methods necessary to solve this problem. This software was created exclusively with free and open source software, so that every aspect of its internal machinery may be scrutinized, replicated, and improved by future workers. / Doctor of Philosophy / Human activities associated with the injection of fluids at depth are known to trigger earthquakes. Many of these earthquakes are small and imperceptible without the aid of specialized instruments, but some may be large enough to pose a significant risk to life and property. Several emerging technologies that have the potential to shape the future of low-carbon energy production, including carbon capture and storage and enhanced geothermal energy production, are inextricably linked to large-scale injection of fluids into the subsurface. The risk of injection-induced earthquakes is a primary concern and potential barrier to widespread adoption of these technologies. New tools are required to help operators manage these risks and meet stakeholder expectations. Current knowledge enables operators to predict the conditions that would trigger such an earthquake, but few or no tools exist to predict the severity of the earthquakes, precluding a complete description of the risk associated with operating a large-scale injection well. This dissertation details the theoretical justification and initial validation of a methodology and software to simulate the motion of an earthquake as it occurs and quantify the severity in terms that are germane to experts in earthquake science. This software was created exclusively with free and open source software, so that every aspect of its internal machinery may be scrutinized, replicated, and improved by future workers.

The object of this thesis is a modestly scaled house at Smith Mountain Lake. The objective of this thesis is to please the senses through material composition. We gain knowledge and sensible understanding of our world through physical interaction and direct sensory experience. Through touching, smelling, listening, and observing we form and guide our choices. These experiences enrich the designer's knowledge of material properties and thus the proper use of materials. The primary focus of this study seeks to understand the physical properties of materials in relation to a site and to each other. Following, it attempts to transform these materials into elements of architecture, as the functional components of a building. Forms derive their unique qualities from these materials; qualities that enrich our consciousness, evoke sensible memories, and fulfill expectations. Chosen for their qualities as well as their perceptions, brick and wood, present a dynamic dialogue about mass in volume.The story of this house is told in relation to how the brick responds to the primary structure and how it orchestrates architectural elements within the whole. The dichotomy between these two materials lends this study to a larger exploration of joinery. The internal joining of wood to wood, or tectonic joining, produces a different expression than the joining of different materials. Wood to brick, for instance produces the legible differentiation of the architectural elements within the house. The arrangement of these materials articulates structure as well as spatial distinctions within the whole. Where volumes detach, glass bridges these materials as its attributes blend the differentiation between an interior and exterior condition. Articulating how these materials meet addresses essential architectural questions of knowledge, thought, and order as well as ephemeral pleasures. To enjoy the physical experience, as it is embraced by all of the senses, is the final goal and desire of this thesis. / Master of Architecture / This quest began by trying to treat one side of a constructed line independently from the other side. Formal distinctions were made, and then later material distinctions in order to treat a building's interior and exterior independently. This thesis study treats the structure independently from the envelope, while creating spatial distinctions within the house through material decisions. Brick and wood were chosen for their contrasting properties, both physically and perceptually. The Brick, with its telluric, of the earth presence, has an obligation to the site, weather, and time. The wood on the other hand, with its tectonic nature, has an obligation to the human touch. The structure, which serves as protection from the elements, its pulled inside to live with the humans as heavy timber posts. The brick is then left to the essential elements of the house, to one day stand as ruins. Namely, the entrance, the hearth, the base, and parts of the envelope, The architectural questions are then asked through material composition and elemental joints.

Many commercial finite element programs support piezoelectric modeling and composite modeling to some extent. The popular program ABAQUS, however, has piezoelectric modeling capabilities only for continuum and one-dimensional truss elements. In situations where aspect ratio constraints and computational inefficiencies become a significant issue, such as modeling very large thin structures, alternate modeling techniques are sometimes required. Much of the focus of this thesis was to introduce equivalent methods for modeling laminated piezoelectric beams and plates. Techniques are derived based on classical beam and plate theory, classical lamination theory, and the linear theory of piezoelectricity. Finite element approximations are used with the principle of minimum potential energy to derive the static equilibrium equations for piezoelectric laminated structures. Equivalent loading techniques are derived based on the constitutive equations of piezoelectricity to simulate actuation forces within the piezoelectric layers. Finite element models using equivalent modeling techniques as well as equivalent loading techniques for piezoelectric laminated structures are developed and compared to ABAQUS models using piezoelectric elements to evaluate the error in theoretical assumptions. The analysis will prove that equivalent structural models and equivalent loading techniques provide excellent means for simplifying the analysis of thin piezoelectric laminated structures. / Master of Science

The Breast Implant Lifetime Study at Virginia Tech, on which this thesis is based, seeks to develop methods and data for predicting the lifetime of saline-filled implants. This research developed Finite Element Analysis (FEA) models to evaluate the stresses that are present in the silicone breast implant material under different loading situations. The FEA work was completed using the commercial codes PATRAN and ABAQUS. PATRAN was used for pre- and post-processing, while ABAQUS was used for the actual analysis and to add fluid and contact elements not supported by PATRAN. Many different loading situations and constraints were applied to these models, as well as variations in the material and model properties. Varying the Poisson's ratio of the implant material from 0.45 to 0.49 did not make a significant difference in the results. Changing the elastic modulus of the implant material from the modulus of a Smooth implant to the modulus of a Siltex implant had a noticeable effect on the stress results, increasing the maximum stresses by almost 8%. Changing the modulus of the surrounding tissue had marked effects as well, with stiffer tissue (E=300 psi) decreasing the implant's stresses by about 60% as compared to softer tissue (E=100 psi). A ten percent decrease in implant thickness yielded a 17% average increase in stress experienced by the implant. For both the 2.5" radius and the 4" radius tissue models, using CAX4 elements produced higher overall stresses in the tissue with the same loading conditions. However, in the 2.5" tissue model, the implant itself experienced less stress with the CAX4 tissue than the CAX3 tissue. In the 4" tissue model, the implant experienced more stress when surrounded by the CAX4 tissue elements. These models will be combined with implant fatigue data to develop a life prediction method for the implant membrane. / Master of Science

This thesis is concerned with the effects of varying the intensity of one element of a compound stimulus while holding the other constant in an experiment employing Kamin’s (1964) design for showing the “perceptual or associative block" in the conditioned emotional response situation. The question of whether Pavlovian "overshadowing” or Hullian "summation” usually obtains during classical compound conditioning is examined. The major findings were (1) that the degree of blocking is a monotonic function of the intensity of the first conditioned element; (2) that rate of conditioning to a compound stimulus is a monotonic function of the intensity of the varied element; and (3) that Hullian summation is the usual case in compound conditioning but that Pavlovian overshadowing occurs when one element is relatively much weaker than the other in terms of speed of conditioning. / Thesis / Master of Arts (MA)