Browsing by Subject "Experiments"
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Item Creating and measuring white dwarf photospheres in a terrestrial laboratory(2014-08) Falcon, Ross Edward; Winget, Donald Earl, 1955-As the ultimate fate of nearly all stars, including our Sun, white dwarfs (WDs) hold rich and informative histories in their observable light. To determine a fundamental parameter of WDs, mass, we perform the first measurement of the average gravitational redshift of an ensemble of WDs. We find a larger mean mass than that determined from the primary and expansive technique known as the spectroscopic method. The potential inaccuracy of this method has broad astrophysical implications, including for our understanding of Type 1a supernova progenitors and for constraining the age of the Universe. This motivates us to investigate the WD atmosphere models used with the spectroscopic method, particularly the input theoretical line profiles, by developing a new experimental platform to create plasmas at WD photospheric conditions (T_e ~ 1 eV, n_e ~ 10^17 cm^-3). Instead of observing WD spectra to infer the plasma conditions at the surface of the star, we set the conditions and measure the emergent spectra in the laboratory. X-rays from a z-pinch dynamic hohlraum generated at the Z Pulsed Power Facility at Sandia National Laboratories irradiate a gas cell to initiate formation of a large (120x20x10 mm or 24 cm^3) plasma. We observe multiple Balmer lines from our plasma in emission and in absorption simultaneously along relatively long (~120 mm) lines of sight perpendicular to the heating radiation. Using a large, radiation-driven plasma aides us to achieve homogeneity along our observed lines of sight. With time-resolved spectroscopy we measure lines at a range of electron densities that spans an order of magnitude, and we do this within one pulsed power shot experiment. Observing our plasma in absorption not only provides the signal-to-noise to measure relative line shapes, it allows us to measure relative line strengths because the lines share the same lower level population. This constrains the theoretical reduction factors used to describe ionization potential depression or the occupation probabilities associated with these Balmer lines. We compare our measured line shapes with the theoretical ones used in WD atmosphere models as part of the first fruits of this rich experimental platform.Item The effect of temperature and terrace geometry on carbonate precipitation rate in an experimental setting(2012-08) Reid, Ellen Elizabeth; Kim, WonsuckThrough flume experiments we demonstrate the calcite precipitation process seen at geothermal hot springs in the lab setting. A series of four experiments were run, varying temperature and terrace ridge height while all other experimental parameters, including initial substrate slope, spring water discharge, and CO₂ input were kept constant. The goal of the experiments was to measure the temperature and terrace height control quantitatively in terms of the amount of overall travertine aggradation, aggradation rate changes in time and downstream direction, as well as to observe the effect of these parameters on processes occurring during precipitation. Using the final deposit thickness measured manually at the end of each experiment and elevation data obtained from a laser topographic profiler, I conclude that high temperature and small terrace heights favor increased precipitation of travertine. However, the amount of precipitation also depends on location within a terrace pond. Flow velocity increases as it approaches a terrace lip, resulting in enhanced precipitation and greater thicknesses in the downstream direction through increased CO₂ degassing, a process called downstream coarsening.Item Essays on the economics of agriculture and energy in Texas(2013-05) Liu, Bing; Benson, Aaron G.; Auld, Dick L.; Malaga, Jaime; Johnson, Phillip N.; Williams, Ryan B.This dissertation is a collection of economic analyses of current agriculture and energy situation in Texas. Considering the current Texas natural resources, these three essays focus on alternative crops that can be introduced into Texas to realize local environmental and societal benefits. The first section presents an assessment of the life-cycle energy and GHG emission impacts associated with winter safflower seed-derived biodiesel to determine its suitability as an energy crop on the Texas High Plains. Winter safflower is considered a potential feedstock for biodiesel production that can be grown on the Texas High Plains. It requires fewer inputs in terms of irrigation and fertilizer than current irrigated crops, and could be grown on semi-arid or marginal land. In addition, this study identifies the factors that have the greatest impact on GHG emissions and the likelihood that winter safflower would be adopted by farmers on the High Plains. Finally, in order to analyze farmers’ planting decisions corresponding to different carbon policies, a production function of safflower and GHG emissions is developed, and a profit maximization model is used to evaluate possible incentives to change behavior. The second section established an econometric supply/demand simulation and forecast model of U.S. corn to quantify the effects of key exogenous variables on the corn supply and demand relationships. The model parameters were estimated through a system of simultaneous equations using the three-stage least squares (3SLS) method, based on annual time-series data from1981 to 2011. Then this model was validated using the Theil’s inequality coefficient. The validated model is expected to forecast a baseline and simulate impacts of plausible scenarios for key exogenous variables in the future. The third section focuses on a new crop, guar, which is considered suitable to be grown on the Texas High Plains to help local farmers to increase revenue. Guar gum is highly valuable and sought after as an ingredient from small quantities in numerous food products to large scale uses in oil field services. Traditionally, much of the guar consumed in the U.S. is imported from India. However, the U.S. energy companies are seeking for stable domestic supply of guar to meet oil field demands. Production contracts are seen as effective methods for maintaining a steady supply of high quality guar seed for processors to ensure their production goals. This current study examined different contract choices that farmers could face in a certain guar production contract. A principle-agent model was established to simulate the incentives inherit in guar production contracts. Specifically, we conducted a choice-based experiment to observe producers’ preferences over different contract attributes. The results of this survey are expected to reveal the value producers place on the different attributes. Finally, the ultimate goal of this study is to determine an efficient contract that will attract sufficient producer participation to ensure a steady supply of high quality guar seed.Item Examining the effect of cemented natural fractures on hydraulic fracture propagation in hydrostone block experiments(2012-08) Bahorich, Benjamin Lee; Olson, Jon E.; Holder, JonMicro seismic data and coring studies suggest that hydraulic fractures interact heavily with natural fractures creating complex fracture networks in naturally fractured reservoirs such as the Barnett shale, the Eagle Ford shale, and the Marcellus shale. However, since direct observations of subsurface hydraulic fracture geometries are incomplete or nonexistent, we look to properly scaled experimental research and computer modeling based on realistic assumptions to help us understand fracture intersection geometries. Most experimental analysis of this problem has focused on natural fractures with frictional interfaces. However, core observations from the Barnett and other shale plays suggest that natural fractures are largely cemented. To examine hydraulic fracture interactions with cemented natural fractures, we performed 9 hydraulic fracturing experiments in gypsum cement blocks that contained embedded planar glass, sandstone, and plaster discontinuities which acted as proxies for cemented natural fractures. There were three main fracture intersection geometries observed in our experimental program. 1) A hydraulic fracture is diverted into a different propagation path(s) along a natural fracture. 2) A taller hydraulic fracture bypasses a shorter natural fracture by propagating around it via height growth while also separating the weakly bonded interface between the natural fracture and the host rock. 3) A hydraulic fracture bypasses a natural fracture and also diverts down it to form separate fractures. The three main factors that seemed to have the strongest influence on fracture intersection geometry were the angle of intersection, the ratio of hydraulic fracture height to natural fracture height, and the differential stress. Our results show that bypass, separation of weakly bonded interfaces, diversion, and mixed mode propagation are likely in hydraulic fracture intersections with cemented natural fractures. The impact of this finding is that we need fully 3D computer models capable of accounting for bypass and mixed mode I-III fracture propagation in order to realistically simulate subsurface hydraulic fracture geometries.Item An experimental and simulation study of the effect of geochemical reactions on chemical flooding(2010-12) Chandrasekar, Vikram, 1984-; Delshad, Mojdeh; Pope, Gary A.The overall objective of this research was to gain an insight into the challenges encountered during chemical flooding under high hardness conditions. Different aspects of this problem were studied using a combination of laboratory experiments and simulation studies. Chemical Flooding is an important Enhanced Oil Recovery process. One of the major components of the operational expenses of any chemical flooding project, especially Alkali Surfactant Polymer (ASP) flooding is the cost of softening the injection brine to prevent the precipitation of the carbonates of the calcium and magnesium ions which are invariably present in the formation brine. Novel hardness tolerant alkalis like sodium metaborate have been shown to perform well with brines of high salinity and hardness, thereby eliminating the need to soften the injection brine. The first part of this research was aimed at designing an optimal chemical flooding formulation for a reservoir having hard formation brine. Sodium metaborate was used as the alkali in the formulation with the hard brine. Under the experimental conditions, sodium metaborate was found to be inadequate in preventing precipitation in the ASP slug. Factors affecting the ability of sodium metaborate to sequester divalent ions, including its potential limitations under the experimental conditions were studied. The second part of this research studied the factors affecting the ability of novel alkali and chelating agents like sodium metaborate and tetrasodium EDTA to sequester divalent ions. Recent studies have shown that both these chemicals showed good performance in sequestering divalent ions under high hardness conditions. A study of the geochemical species in solution under different conditions was done using the computer program PHREEQC. Sensitivity studies about the effect of the presence of different solution species on the performance of these alkalis were done. The third part of this research focused on field scale mechanistic simulation studies of geochemical scaling during ASP flooding. This is one of the major challenges faced by the oil and gas industry and has been found to occur when sodium carbonate is used as the alkali and the formation brine present in situ has a sufficiently high hardness content. The multicomponent and multiphase compositional chemical flooding simulator, UTCHEM was used to determine the quantity and composition of the scales formed in the reservoir as well as the injection and production wells. Reactions occurring between the injected fluids, in situ fluids and the reservoir rocks were taken into consideration for this study. Sensitivity studies of the effect of key reservoir and process parameters like the physical dispersion and the alkali concentration on the extent of scaling were also done as a part of this study.Item Hydraulic fracturing optimization : experimental investigation of multiple fracture growth homogeneity via perforation cluster distribution(2016-05) Michael, Andreas; Olson, Jon E.; Balhoff, Matthew THydraulic fracturing is a reservoir stimulation technique used in the petroleum industry since 1947. High pressure fluid composed mainly of water generates cracks near the wellbore improving the surrounding permeability and enhancing the flow of oil and gas to the surface. Advances in hydraulic fracturing coupled with developments in horizontal drilling, have unlocked vast quantities of unconventional resources, previously believed impossible to be produced. Fracture creation induces perturbations in the nearby in-situ stress regime suppressing the initiation and propagation of other fractures. Neighboring fractures are affected by this stress shadow effect, causing them to grow dissimilarly and they receive unequal portions of the injected fluid. Numerical simulation models have shown that non-uniform perforation cluster distributions with interior fractures closer to the exterior ones can balance out these stress shadow effects, promoting more homogeneous multiple fracture growth compared to uniform perforation cluster distributions. In this work, laboratory-scale tests on three perforation configurations are performed on transparent specimens using distinctly colored fracturing fluids such that fracture growth can be observed. A normal faulting stress regime is replicated with the introduction of an overburden load in a confined space. The results have shown that uniform perforation spacing configurations yields higher degree of fracture growth homogeneity, as maximum spacing minimizes stress shadow effects, compared to moving the middle perforation closer to the toe, or heel of the horizontal well. The experiments also showed a proclivity to form one dominant fracture. Time delay, neglected in most theoretical modelling studies, between fracture initiations is found to be a key parameter and is believed to be one of the major factors promoting this dominant fracture tendency along with wellbore pressure gradients. Moreover, in several cases, the injected bypassed perforation(s) to generate fracture(s) downstream. Finally, the compressibility of the fracturing fluid triggered somewhat unexpected transient pressure behavior. The understanding of the stress shadow effects and what influences them could lead to optimization of hydraulic fracturing treatment design in terms of productivity and cost. Therefore, achieving more homogeneous multiple fracture growth patterns can be pivotal on the economic feasibility of several stimulation treatments.Item Implementation and comparison of cosine modulated filter banks on a fixed point digital signal processor(Texas Tech University, 2004-05) Bhate, Kedar RavindraCosine Modulated Filter Banks have an efficient structure with respect to the number of multiplication and delay elements required. They also provide another desirable feature, perfect reconstruction (PR). However, their ability to provide PR can be affected due to various parameters, such as fixed-point constraints, imperfect modulation matrix, etc. In this thesis, effects of these parameters on the ability of the filter bank to provide PR are studied. To demonstrate the use of the filter bank in a real- time application, it is implemented using a TMS320C6211 Fixed-point Digital Signal Processor (DSP). The implementation uses the TLC320AD535 audio Encoder/Decoder (CODEC), the Multichannel Buffered Serial Port (McBSP) and the Enhanced Direct Memory Access (EDMA) controller on the DSK6211 board to continuously process and reconstruct digitized audio data.Item The instability of incivility : how news frames and citizen perceptions shape conflict in American politics(2013-12) Muddiman, Ashley Rae; Stroud, Natalie JominiPoliticians and media elites have been calling for a return to civility in United States politics, and the vast majority of citizens agree that civility is necessary for a strong democracy. Yet incivility is an ever-present and misunderstood part of politics. In my dissertation, I focus on news, politics, and incivility by asking three questions. First, to what extent does news coverage portray political conflict as uncivil? Second, what political behaviors do citizens perceive as uncivil? Finally, how does news that portrays politics as uncivil affect citizens? I used a mixed method approach to answer these questions. I, first, conducted a content analysis of news surrounding four high-conflict political events to determine whether two conflict frames (interpersonal-level and public-level conflict) emerged. Second, I conducted two experiments and drew from social judgment theory to determine whether citizens perceived multiple types of incivility and whether their partisanship influenced how acceptable they found political behaviors to be. In a final experiment, I tested whether exposure to mediated conflict frames prompted perceptions of incivility from citizens and affected their reactions to politics. This project makes clear that news coverage of conflict emphasizes incivility and negatively affects citizens. Media elites shape political conflict using interpersonal-level and public-level conflict frames. Citizens perceive both types of conflict, as well, and tend to think that likeminded partisans are behaving appropriately while counter-attitudinal partisans are behaving badly. Finally, and importantly, the coverage of political conflict affects citizens in troublesome ways. Particularly when both types of conflict frames are present in the news, citizens feel more anxiety and aversion, have decreased levels of favorability toward political institutions, and think of political arguments in partisan ways. Overall, I conclude that incivility is not stable. Instead, incivility is a two-dimensional concept that is shaped by the media, perceived by citizens, and advanced by partisans. By recognizing these dimensions of incivility, researchers may find new and important effects of incivility, and people interested in ridding politics of incivility may be more successful by beginning with the recognition that what is uncivil to one person is not always uncivil to another.Item Real significance of online breaking news : examining the credibility of online breaking news(2013-12) Yoo, Joseph Jai-sung; Coleman, RenitaBreaking news implies that something urgent, important and newsworthy happened, assuming that viewers will be more curious about this event. As the mass media have continued to develop, the form of breaking news also keeps on changing. Today, the internet plays a primary role as a platform of breaking news. With online news services providing a plethora of real-time breaking news to audiences, there is a concern that online breaking news has little news value. Some scholars warned that the increase in the number of breaking news would finally impoverish the quality of journalism. Thus, this study tried to ascertain the credibility of online breaking news. This study conducted a 2 (news with/without breaking label) ⅹ 2 (high and low news value) factorial-designed experiment. The result of the experiment suggested that neither breaking news label nor newsworthiness would not increase or decrease the credibility rating. It would be possible to assume that there was no effect of such two components because audiences have already grown accustomed to the prevalence of the label breaking news and continual update of the headline of online news. Journalists might arbitrarily label specific news as breaking news, but they would keep in mind that calling something “breaking news” neither helps nor hurts.Item Three experiments on decision-making under uncertainty in dynamic environments(2013-05) Rosokha, Yaroslav; Stahl, Dale O.This dissertation consists of three economic experiments that investigate behavioral differences in decision making process under risk (uncertainty with known probabilities) and under ambiguity (uncertainty with unknown probabilities). The first and the second chapters present two experiments with subjects choosing between lotteries involving risky and ambiguous urns. Decisions are made in conjunction with a sequence of random draws with replacement, allowing us to track the beliefs of the agents at different moments in time. In the first chapter, we develop and estimate a model of subjective belief updating allowing for base rate fallacy. We find that when updating under ambiguity subjects significantly underweight the new signal, while when updating under compound risk subjects are essentially Bayesian. In the second chapter, we estimate a popular multiple priors model for decision making under ambiguity in dynamic environments. Our estimates suggest a difference in the confidence with which subjects discard the unlikely priors depending on whether an ambiguous urn was presented first or second. Specifically, when an ambiguous urn is presented first, subjects consider more priors during the learning process as compared to when a compound urn is presented first. We also find significant evidence against the hypothesis that human subjects consider only Dirac priors. In the third chapter, we examine the behavior of security dealers in an environment where the level of asymmetric information is viewed as either risk, compound risk, or ambiguity. Using two measures of market liquidity, resiliency and price, we find that duopoly dealer markets are both more resilient to uncertainty about asymmetric information as well as having higher dealer bids compared with monopoly dealer markets for all three uncertainty scenarios. Additionally, we find differences in dealer bidding behavior in duopoly setting depending on whether the uncertainty about informed trading is presented as risk, compound risk, or ambiguity.