<p>In order to determine the parent stellar sites for the presolar grains of potential nova origin, it is crucial to know the rates of the thermonuclear reactions which affect the Si production and destruction in novae. One such reaction is the ²⁹P(p, gamma)³⁰S. This reaction also influences type I X-ray bursts. The energy generation and nucleosynthesis in the burst, along with its duration and light-curve structure, are very sensitive to the reaction flow through a few waiting-point nuclei along the rp- and ap-process paths. In particular, network calculations show that the waiting-point nucleus ³⁰S (t_1/2 = 1175.9(17) ms) is critical.</p> <p>The structure of proton-unbound ³⁰S states strongly determines the thermonuclear ²⁹P(p, gamma)³⁰S reaction rate at temperatures characteristic of explosive hydrogen burning in classical novae and type I X-ray bursts (0.1 ≤ T ≤ 1.3 GK). Specifically, the rate had been previously predicted to be dominated by two low-lying, unobserved, J^pi= 3⁺and 2⁺ levels in the E_x = 4.7 to 4.8 MeV region.</p> <p>The 3⁺resonance was observed a few years ago via a ³²S(p, t)³⁰S measurement. However, the 2⁺resonance remained unobserved. To search for it, we have performed a higher energy resolution charged-particle spectroscopy and an in-beam gamma-ray spectroscopy to investigate the level structure of ³⁰S above the proton threshold via the ³²S(p, t)³⁰S and ²⁸Si(³He, n-gamma)³⁰S reactions, respectively.</p> <p>In this work we provide a description of the experimental setup, data analysis and results of both experiments. Moreover, we have calculated the ²⁹P(p, gamma)³⁰S reaction rate via the state-of-the-art Monte Carlo technique, and have investigated the impact of this updated rate on the abundances of elements synthesized in novae, including those of silicon isotopes.</p> / Doctor of Philosophy (PhD)

<p> Natural peatlands are an important component of the global carbon cycle representing a net long-term sink of atmospheric carbon dioxide (CO2). The natural carbon storage function of these ecosystems can be severely impacted due to peatland drainage and peat extraction leading to large and persistent sources of atmospheric CO2 following peat extraction abandonment. Moreover, the cutover peatland has a low and variable water table position and high soil-water tension at the surface which creates harsh ecological and microclimatic conditions for vegetation reestablishment, particularly peat-forming Sphagnum moss. Standard restoration techniques aim to restore the peatland to a carbon accumulating system through various water management techniques to improve hydrological conditions and by reintroducing Sphagnum at the surface. However, restoring the hydrology of peatlands can be expensive due to the cost of implementing the various restoration techniques. The goal of this study is to examine a new extraction-restoration technique where the acrotelm is preserved and replaced on the cutover surface. More specifically, this thesis examines the effects of an acrotelm transplant experiment on the hydrology (i.e. water table, soil moisture and soil-water tension) and peatland-atmosphere CO2 exchange at a cutover peatland.</p> <p> The experimental acrotelm restoration technique maintained both high water table and moisture conditions providing sufficient water at the surface for Sphagnum moss. Furthermore, the high moisture conditions and low soil-water tensions compared to an adjacent natural site were maintained well above the measured critical Sphagnum threshold of 33% (-100 mb) VMC further providing favourable conditions for Sphagnum moss survival and growth.</p> <p> Peat respiration at the experimental restored acrotelm (110.5 g C m-2) was considerably lower than the natural peatland (144.8 and 203.7 g C m-2). However, gross ecosystem production (GEP) at the experimental site (-54.0 and -34.4 g C m-2) was significantly reduced compared to the natural site (-179.2 and -162.0 g C m-2). Consequently this resulted in a shift towards a net source of CO2 to the atmosphere over the season at the experimental site (78.5 and 56.5 g C m-2) and a sink of CO2 at the natural site (-17.6 and -22.8 g C m-2).</p> <p> Light response curves indicated that maximum GEP was considerably lower at the experimental site; however it is likely that the percentage of living and dead vegetation at the plots post restoration had a large control on this lower productivity as plots with more living vegetation had higher overall productivity (GEP). Despite wetter conditions at the experimental site, large diurnal variations in moisture (~30%) were observed suggesting disturbance to the peat structure. Although soil-water retention analysis and physical peat properties indicated that no apparent structural change in peat structure occurred, it is theorized that a change in volume in the capitula may enhance the wetting and drying cycles in moisture. Lateral expansion/contraction within the peat matrix may occur due to spaces (gaps/fissures) left between the replaced acrotelm blocks from the extraction-restoration process promoting large changes in moisture which consequently can affect the gas exchange process at the surface. Large changes in peat and capitual moisture have been shown to affect productivity leading to variable GEP and enhanced respiration, making it important to limit the moisture variability at the surface from a carbon cycling perspective. Therefore it is likely that a combination of both physiological health of the vegetation and wetting/drying cycles contributed to lower GEP, suggesting the importance of limiting disturbance at the surface during the extraction and restoration process.</p> <p> The new extraction-restoration technique has potential to return a peatland to both near-natural hydrological conditions and towards a net sink of atmospheric CO2. The replaced acrotelm on the cutover surface aided in maintaining adequate moisture conditions thereby provided adequate conditions for Sphagnum survival and reestablishment. However, the ability of the system to remain a net sink of CO2 as like the natural site was not observed post-disturbance due to differences in productivity. Nevertheless, the experimental site did maintain limited productivity post-extraction indicating that the carbon dynamics of the system was maintained due to this acrotelm restoration process potentially returning the ecosystem towards a natural sink of atmospheric CO2 over a longer period time.</p> / Thesis / Master of Science (MSc)

No description available.

The development of hydrocarbon energy resources from shale, a fine-grained, low-permeability geological formation, has altered the global energy landscape. Constricting pressure exerted on a shale formation has a significant effect on the rock's apparent permeability. Gas flow in low-permeability shales is significantly different from liquid flow due to the Klinkenberg effect caused by gas molecule slip at the nanopore wall surfaces. This has the effect of increasing apparent permeability (i.e., the measured permeability). Optimizing the conductivity of the proppant assembly is another critical component of designing subsurface hydrocarbon production using hydraulic fracturing. Significant fracture conductivity can be achieved at a much lower cost than conventional material costs, according to the optimal partial-monolayer proppant concentration (OPPC) theory. However, hydraulic fracturing performance in unconventional reservoirs is problematic due of the complex geomechanical environment, and the experimental confirmation and investigation of the OPPC theory have been rare in previous studies. In this dissertation, a novel multiphysics shale transport (MPST) model was developed to account for the coupled multiphysics processes of geomechanics, fluid dynamics, and the Klinkenberg effect in shales. Furthermore, A novel multi-physics multi-scale multi-porosity shale gas transport (M3ST) model was developed based on the MPST model research to investigate shale gas transport in both transient and steady states, and a double-exponential empirical model was also developed as a powerful substitute for the M3ST model for fitting laboratory-measured apparent permeability. Additionally, throughout the laboratory experiment of fracture conductivity with proppant, the four visible stages documented the evolution of non-monotonic conductivity and proppant concentration. The laboratory methods and empirical model were then applied to the shale plugs from Central Appalachia to investigate the formation properties there. The benefits of developing these regions wisely include a smaller surface footprint, reduced infrastructure requirements, and lower development costs. The developed MPST, M3ST, double-exponential empirical models and research findings shed light on the role of multiphysics mechanisms, such as geomechanics, fluid dynamics and transport, and the Klinkenberg effect, in shale gas transport across multiple spatial scales in both steady and transient states. The fracture conductivity experiments successfully validate the theory of OPPC and illustrate that proppant embedment is the primary mechanism that causes the competing process between fracture width and fracture permeability and consequently the non-monotonic fracture conductivity evolution as a function of increasing proppant concentration. The laboratory experimental facts and the numerical fittings in this study provided critical insights into the reservoir characterization in Central Appalachia and will benefit the reservoir development using non-aqueous fracturing techniques such as CO2 and advanced proppant technologies in the future. / Doctor of Philosophy / Production of oil and gas from the extremely tight rock has changed the global energy industry, including job growth, energy security, and environment protection. However, the oil and gas production from the tight rock is difficult because of the complex rock properties. Hydraulic fracking can resolve the issue and contribute to the high production. The higher and safer production needs us to have a better understanding of oil and gas flow under the ground. A series of laboratory experiment were conducted, and a new shale gas transport model is introduced in this dissertation to explain the oil and gas flow under the complicated scenarios. The experimental results show that many factors can impact the oil and gas flow, and the model can match the experimental results very well. A few statistical methods are also used in the data analysis. The optimization of proppant pack is another important component of hydraulic fracking. Proppant particles are usually man-made ceramic tiny balls, which will be injected into the underground to keep the fractures from closing during the production. From the previous papers, it is possible to achieve high fracture conductivity at a much lower cost than traditional proppant costs. Many groups of laboratory experiment were conducted to demonstrate this guess. Many rock samples in the experiment are from Central Appalachian area, which can help the resource development in this area. The developed model and experimental research findings in this study provided critical insights into the role of the many physics mechanisms on shale gas transport, proppant optimization, and hydraulic fracking.

This dissertation is comprised of three essays that investigate consumer behavior and health outcomes. The first essay uses experimental economic techniques to explore consumers' preferences and willingness to pay (WTP) for nutritionally differentiated grass-fed beef. Our findings suggest that consumers' nutrition knowledge about the functions of Vitamin A, Vitamin E, CLA, and Omega 3 could positively affect their WTP for grass-fed beef while the knowledge about the main food sources of these nutrients negatively affects their WTP for grass-fed beef. Furthermore, a higher sensory evaluation score of grass-fed beef compared to conventional beef will lead to a higher probability for a consumer to choose grass-fed beef and a higher monetary value she/he is willing to pay for grass-fed beef. Using the same experimental data collected in the first study, the second essay investigates the impacts of consumers' nutrition knowledge on their WTP by accommodating the potential endogeneity problem using an instrumental variable approach and a non-instrumental variable approach. Our results suggest the existence of the endogeneity of nutrition knowledge and indicate that ignoring the endogeneity problem in econometric modeling will downwardly bias the estimates of the true effects of nutrition knowledge. The estimates obtained from different estimation strategies in the study indicate the robustness of our findings about the effects of nutrition knowledge on consumers' food purchasing behavior. The third essay investigates the impacts of primary care giver (PCG)'s time allocation patterns and household food expenditure choices on childhood obesity using the national panel study of income dynamics data. Our results do not suggest significant impacts of PCG's labor force participation, involvement in children's outdoor activity, and household food expenditures on children's Body Mass Index (BMI). However, the estimates from iterated seemingly unrelated regression (SUR) and semi-parametric polynomial estimation indicate that parents' BMI significantly influence children's BMI. Interestingly, physical activity appears to have weak correlation with children's BMI. / Ph. D.

Coastal regions are vulnerable to various natural processes, ranging from normal waves to extreme events. Given the flourishing development and large population along coastlines, various measures have been taken to mitigate the water-induced damage. Nature-based coastal protection, especially vegetation, has attracted unprecedented studies over the past two decades. To enhance understanding of this subject, this dissertation evaluates the impact of patchy vegetation on wave and runup dynamics along coastlines. Selecting from a prototype in Dalehite Cove, Galveston Bay, TX, results from a Boussinesq model (COULWAVE) showed patchy vegetation reduced up to 75% mean shoreward current in the mound-channel wetland systems. These vegetation patches also reduced the primary circulation around mounds, with a power-form relation between circulation size and various parameters (i.e., bathymetry, incident wave and vegetated roughness). Substituting spectral waves for regular waves in the similar wetlands, more energy was transferred into the higher frequencies. The impact of patchy vegetation on wave energy was frequency- and space-dependent, with increased energy observed in specific harmonics and locations. Comparison with unvegetated horizontal bathymetry demonstrated that mound-channel bathymetry was the dominant factor in transferring and dissipating wave energy, while vegetation patches added a fair contribution. As for extreme events, such as tsunamis, laboratory experiments and numerical simulations were conducted to assess the effectiveness of patchy vegetation with various roughness levels, spacings and sizes. Overall, vegetation patches reduced the most destructive loads onshore by up to 80%. Within-patch roughness variation only caused uncertainty on the hydrodynamics around the seaward patches, while the mitigation of extreme loads was not undermined. A logarithmic relation was observed between the protected area from extreme loads and the vegetated coverage. These findings will fill the knowledge gap of hydrodynamics in the presence patchy vegetation, and improve the engineering practice of coastal protection using nature-based infrastructure. / Ph. D.

Satisfactory systems of confounding for symmetrical factorial experiments can be constructed oy the familiar methods, using the. theory of Galois fields. Although these methods can be extended to asymmetrical factorial experiments· (White and Hultquist, 1965; Raktoe, 1969) the actual construction of designs becomes much mor:e complicated for the general case and does not always lead to satisfactory plans. A different approach to this problem is to consider balanced factorial experiments (BFE), due to Shah (1958, 1960). Such BFE have a one-to-one relationship to EGD-PBIB designs given by Hinkelmann (1964). The problem of constructing BFE is then equivalent to constructing EGD-PBIB designs. A new method is proposed here to construct such designs. This method is based upon the so-called (1,1, ...,1)th-associate matrix and the operations symbolic direct product (SDP), generalized symbolic direct product (GSDP), symbolic direct multiplication (SDM), and generalized symbolic direct multiplication (GSDM). Let A₁ , A₂, ... , A_n be n factors in a factorial experiment, with A_i having t_i levels (i = 1, 2, ... , n). It is shown that an EGD-PBIB design with blocks of size t_i can be constructed, provided that t_iᵢ ≠ max ( t₁ , t₂, . . . , t_n ). This method is more general and more flexible than the method of Aggarwal (1974) in that any two treatment combinations can be γ-th associates where γ has at least two unity components, and it can be shown the number of possible candidates for such is 2^{n-i l} -1 for blocks of size t_i (i = 1, 2, .. , n -1), where t₁ < t₂ <...< t_n. This method is also more general than the Kronecker product method due to Vartak (1955}. Two types of PBIB designs· are used for reducing the numbers of associa,te classes in EGD-PBIB designs. When the t_i (i = 1, 2, ... , n) are equal, then some EGD-PBIB designs can be reduced to a hypercubic design. The EGD-PBIB designs with block size π [below jεA] t_j, where A is an arbitrary subset of the set {1, 2, ... , n} can be reduced to newly introduced F_A⁽ⁿ⁾-type PBIR designs. Since BFE results very often in designs with a large number of blocks, the notion of partial balanced factorial experiment (PBFE) has been introduced. It is investigated how such designs can be constructed and related to PBIB-designs similar to that between BFE and EGD-PBIB designs. Two new types of PBIB designs have been introduced in this context. / Ph. D.

Conservation agriculture has many potential benefits for small farmers. This study seeks to estimate the value that farmers in eastern Uganda place on some these benefits. Data from a choice experiment study are analyzed with a mixed logit model to determine farmers' willingness to pay for increases in maize yield, reductions in erosion, and reductions in land preparation labor requirements. It finds that farmers have a statistically significant willingness to pay for increases in yield and reductions in erosion, but not for reductions in planting labor. In addition, farmers in Kapchorwa district value erosion control and labor reductions more and price increases less than in Tororo district, while women care more about price increases than men do. / Master of Science / CCRA-6 (Economic and Impact Analysis)

Primarily via constructivist teaching experiment methodology, units coordination (Steffe, 1992) has emerged as a useful construct for modeling students' psychological constructions pertaining to several mathematical domains, including counting sequences, whole number multiplicative conceptions, and fractions schemes. I describe how consideration of units coordination as a Piagetian (1970b) structure is useful for modeling units coordination across contexts. In this study, I extend teaching experiment methodology (Steffe and Thompson, 2000) to model the dynamics of students' units coordinating activity across contexts within a teaching experiment, using the construct of propensity to coordinate units. Two video-recorded teaching experiments involving pairs of sixth-grade students were analyzed to form a model of the dynamics of students' units coordinating activity. The modeling involved separation of transcriptions into chunks that were coded dichotomously for the units coordinating activity of a single student in each dyad. The two teaching experiments were used to form 5 conjectures about the output of the model that were then tested with a third teaching experiment. The results suggest that modeling units coordination activity via the construct of propensity to coordinate units was useful for describing patterns in the students' perturbations during the teaching sessions. The model was moderately useful for identifying sequences of interactions that support growth in units coordination. Extensions, modifications, and implications of the modeling approach are discussed. / Ph. D.

Nitrate (NO⁻3) export can vary widely among forested watersheds with similar nitrogen loading, geology, and vegetation, which suggests the importance of understanding differing internal retention mechanisms. Transport should be studied at the hillslope scale because the hillslope is the smallest unit with spatial and temporal resolution to reflect many relevant NO⁻3 retention and transport (flow-generation) processes, and headwater forested watersheds are largely comprised of sections of hillslopes. I conducted two experiments to elucidate subsurface flow dynamics and NO⁻3 transport and retention mechanisms on a constructed experimental hillslope model. In the first experiment, I tested whether decadal pedogenetic changes in soil properties in the experimental hillslope used by Hewlett and Hibbert (1963) would lead to changes in recession flow. I repeated (twice) their seminal experiment, whose results led to the development of the Variable Source Area paradigm, by also saturating, covering, and allowing the experimental hillslope to drain until it no longer yielded water. In the historical experiment there was fast drainage for 1.5 d, followed by slow drainage for ~140 d, which led the authors to conclude that recession flow in unsaturated soil could sustain baseflow throughout droughts. This long, slow drainage period was not reproduced in my experiments. Shapes of the drainage curves in my experiments were similar to the historical curve, but slow drainage was truncated, ending after 17 and 12 d, due likely to a leak in the boundary conditions, rather than to pedogenetic changes since the historical experiment. Leakage to bedrock, analogous to the leak in the hillslope model, is a commonly observed phenomenon and this study highlights how that can reduce drainage duration and the contribution of moisture from soils to support baseflow. In the second experiment, I tested whether movement of NO⁻3, which is considered a mobile ion, would be delayed relative to movement of water through a hillslope. I added concentrated pulses of ¹⁵NO⁻3 and a conservative tracer (²H₂O) on the same experimental hillslope, which was devegetated and irrigated at hydrologic steady state. Retention of the ¹⁵NO⁻3 tracer was high in the soil surface (0–10 cm) layer directly where the tracer was added. The portion of the ¹⁵NO⁻3 tracer that passed through this surface layer was further retained/removed in deeper soil. The reduction in the peaks in δ¹⁵N breakthrough was an order of magnitude larger than in δ₂H breakthrough at the outlet 5 m downslope of the tracer addition. The peaks in δ¹⁵N were also delayed relative to the peaks in δ₂H by 1, 6, 9 and 18.5 d for slope distances of 0, 2, 4, and 5 m, respectively, from tracer addition to the outlet. The excess mass of ¹⁵NO⁻3 recovered at the outlet was less than 3% of the original tracer mass injected. Nitrification and denitrification were estimated to be roughly 1:1 and were large fluxes relative to lateral transport into and out of the riparian zone. This tracer experiment shows that bedrock leakage, coupled with multiple retention/removal mechanisms can significantly delay export of added NO⁻3 with implications of additional NO⁻3 sink strength at the watershed scale. / Ph. D. / Nitrate (NO₃⁻) export can vary widely among forested watersheds with similar nitrogen loading, geology, and vegetation, which suggests the importance of understanding differing internal process mechanisms. I conducted two experiments to illustrate how water and NO₃⁻ moved on a constructed hillslope model. In the first experiment, I quantified differences in soil properties in the hillslope model used by Hewlett and Hibbert (1963). Then I repeated (twice) the seminal drainage experiment described in Hewlett and Hibbert (1963). The same hillslope (21.8°; 40%) was wetted up, covered, and allowed to drain until water stopped exiting at the outlet. In the historical experiment there was fast drainage for 1.5 d, followed by slow drainage for ~140 d, which led the authors to hypothesize that slow drainage in surface soil could continually contribute water to streams even during droughts. This long, slow drainage period was not reproduced in my experiments. Drainage was similar at the beginning of drainage between my experiments and the historical experiment, but in my experiment the slow drainage ended earlier (after 17 and 12 d) due likely to a leak in the constructed hillslope model, rather than to significant changes that occurred in the soil itself since the original experiment. This leak in the hillslope model is similar to leakage to bedrock, which is commonly observed in natural hillslopes. In the second experiment, I tested whether NO₃⁻ and water would move through a hillslope at the same rate. I added concentrated pulses of NO₃⁻ (as ¹⁵NO₃⁻ and water (as ²H₂O) on the same devegetated experimental hillslope. Retention of the ¹⁵NO₃⁻ tracer was high in the surface (0–10 cm) where the tracer was added, with little change in the immediately surrounding soil, despite high rates of water input immediately after tracer addition and throughout the experiment. The portion of the ¹⁵NO₃⁻ tracer that passed through the surface layer was further processed by microbes in deeper soil as it traveled downslope. This body of work shows that bedrock leakage, coupled with multiple retention mechanisms throughout the soil profile, can significantly delay export of added NO₃⁻ at the watershed scale.