Matching Items (43,913)
Description
Fuel cells, particularly solid oxide fuel cells (SOFC), are important for the future of greener and more efficient energy sources. Although SOFCs have been in existence for over fifty years, they have not been deployed extensively because they need to be operated at a high temperature (∼1000 °C), are expensive, and have slow response to changes in energy demands. One important need for commercialization of SOFCs is a lowering of their operating temperature, which requires an electrolyte that can operate at lower temperatures. Doped ceria is one such candidate. For this dissertation work I have studied different types of doped ceria to understand the mechanism of oxygen vacancy diffusion through the bulk. Doped ceria is important because they have high ionic conductivities thus making them attractive candidates for the electrolytes of solid oxide fuel cells. In particular, I have studied how the ionic conductivities are improved in these doped materials by studying the oxygen-vacancy formations and migrations. In this dissertation I describe the application of density functional theory (DFT) and Kinetic Lattice Monte Carlo (KLMC) simulations to calculate the vacancy diffusion and ionic conductivities in doped ceria. The dopants used are praseodymium (Pr), gadolinium (Gd), and neodymium (Nd), all belonging to the lanthanide series. The activation energies for vacancy migration between different nearest neighbor (relative to the dopant) positions were calculated using the commercial DFT code VASP (Vienna Ab-initio Simulation Package). These activation energies were then used as inputs to the KLMC code that I co-developed. The KLMC code was run for different temperatures (673 K to 1073 K) and for different dopant concentrations (0 to 40%). These simulations have resulted in the prediction of dopant concentrations for maximum ionic conductivity at a given temperature.
ContributorsAnwar, Shahriar (Author) / Adams, James B (Thesis advisor) / Crozier, Peter (Committee member) / Krause, Stephen (Committee member) / Arizona State University (Publisher)
Created2011
Description
An array of north-striking, left-stepping, active normal faults is situated along the southwestern margin of the Gulf of California. This normal fault system is the marginal fault system of the oblique-divergent plate boundary within the Gulf of California. To better understand the role of upper-crustal processes during development of an obliquely rifted plate margin, gravity surveys were conducted across the normal-fault-bounded basins within the gulf-margin array and, along with optically stimulated luminescence dating of offset surfaces, fault-slip rates were estimated and fault patterns across basins were assessed, providing insight into sedimentary basin evolution. Additionally, detailed geologic and geomorphic maps were constructed along two faults within the system, leading to a more complete understanding of the role of individual normal faults within a larger array. These faults slip at a low rate (0.1-1 mm/yr) and have relatively shallow hanging wall basins (~500-3000 m). Overall, the gulf-margin faults accommodate protracted, distributed deformation at a low rate and provide a minor contribution to overall rifting. Integrating figures with text can lead to greater science learning than when either medium is presented alone. Textbooks, composed of text and graphics, are a primary source of content in most geology classes. It is essential to understand how students approach learning from text and figures in textbook-style learning materials and how the arrangement of the text and figures influences their learning approach. Introductory geology students were eye tracked while learning from textbook-style materials composed of text and graphics. Eye fixation data showed that students spent less time examining the figure than the text, but the students who more frequently examined the figure tended to improve more from the pretest to the posttest. In general, students tended to examine the figure at natural breaks in the reading. Textbook-style materials should, therefore, be formatted to include a number of natural breaks so that learners can pause to inspect the figure without the risk of losing their place in the reading and to provide a chance to process the material in small chunks. Multimedia instructional materials should be designed to support the cognitive processes of the learner.
ContributorsBusch, Melanie M. D (Author) / Arrowsmith, Ramon (Thesis advisor) / Reynolds, Stephen (Thesis advisor) / Chi, Michelene (Committee member) / Semken, Steven (Committee member) / Tyburczy, James (Committee member) / Arizona State University (Publisher)
Created2011
Description
Type Ia supernovae are important, but mysterious cosmological tools. Their standard brightnesses have enabled cosmologists to measure extreme distances and to discover dark energy. However, the nature of their progenitor mechanisms remains elusive, with many competing models offering only partial clues to their origins. Here, type Ia supernova delay times are explored using analytical models. Combined with a new observation technique, this model places new constraints on the characteristic time delay between the formation of stars and the first type Ia supernovae. This derived delay time (500 million years) implies low-mass companions for single degenerate progenitor scenarios. In the latter portions of this dissertation, two progenitor mechanisms are simulated in detail; white dwarf collisions and mergers. From the first of these simulations, it is evident that white dwarf collisions offer a viable and unique pathway to producing type Ia supernovae. Many of the combinations of masses simulated produce sufficient quantities of 56Ni (up to 0.51 solar masses) to masquerade as normal type Ia supernovae. Other combinations of masses produce 56Ni yields that span the entire range of supernova brightnesses, from the very dim and underluminous, with 0.14 solar masses, to the over-bright and superluminous, with up to 1.71 solar masses. The 56Ni yield in the collision simulations depends non-linearly on total system mass, mass ratio, and impact parameter. Using the same numerical tools as in the collisions examination, white dwarf mergers are studied in detail. Nearly all of the simulations produce merger remnants consisting of a cold, degenerate core surrounded by a hot accretion disk. The properties of these disks have strong implications for various viscosity treatments that have attempted to pin down the accretion times. Some mass combinations produce super-Chandrasekhar cores on shorter time scales than viscosity driven accretion. A handful of simulations also exhibit helium detonations on the surface of the primary that bear a resemblance to helium novae. Finally, some of the preliminary groundwork that has been laid for constructing a new numerical tool is discussed. This new tool advances the merger simulations further than any research group has done before, and has the potential to answer some of the lingering questions that the merger study has uncovered. The results of thermal diffusion tests using this tool have a remarkable correspondence to analytical predictions.
ContributorsRaskin, Cody (Author) / Scannapieco, Evan (Thesis advisor) / Rhoads, James (Committee member) / Young, Patrick (Committee member) / Mcnamara, Allen (Committee member) / Timmes, Francis (Committee member) / Arizona State University (Publisher)
Created2011
Description
La frontera entre México y Estados Unidos es un territorio que se ha conceptualizado y construido por el centralismo mexicano y por el discurso chicano dominante: el de Borderlands. Estos dos focos equidistantes establecen sus perspectivas a partir del contacto que la región fronteriza tiene con los Estados Unidos en términos de intercambios económicos y culturales. La tradición de definir la zona fronteriza se inicia a partir de 1848 con el Tratado de Guadalupe Hidalgo. Más tarde, dicha región estaría en indiferencia por su distancia geográfica con el centro mexicano, excepto durante la Revolución mexicana. Sin embargo, la región fronteriza empieza a recibir gran atención hacia finales del Siglo XX, cuando nuevas formas de intercambio económico entre México y Estados Unidos se empiezan a desarrollar. La frontera, entonces experimenta un crecimiento económico que se refleja, a su vez, en el resurgimiento y crecimiento de la cultura fronteriza. El antropólogo cultural, Nestor García Canclini intentó definir la cultura fronteriza al analizar el uso del idioma inglés en Tijuana. En sus estudios, tanto Tijuana: la casa de toda la gente (1989) como Culturas híbridas: Cómo entrar y salir de la modernidad (1992), García Canclini sostiene que la frontera es un espacio de hibridación cultural. Por otro lado, las teorías dominantes dentro del campo chicano definen la frontera en términos metafísicos. Para Gloria Anzaldúa, el espacio fronterizo es el Borderlands: un área geográfica en donde los paradigmas de la psicología del individuo están en constante conflicto. Considerando estos antecedentes como punto de partida, esta investigación se enfoca en el estudio de la cultura fronteriza como múltiples universos de signos que entran en contacto unos con otros. Tal como lo establece Iury Lotman en su estudio teórico La semiosfera (1996), una semiosfera es un espacio delimitado por una frontera que, a su vez, tiene la función de traducir información de otras semiosferas. De manera que dicho concepto se muestra adecuado para analizar El gran preténder (1992) de Luis Humberto Crosthwaite y Berlín 77 (y otros relatos) (2003) de Carlos Adolfo Gutiérrez Vidal. En última instancia, al establecer los espacios fronterizos como universos culturales (semiosferas) se devela el nivel de contacto entre éstas, especialmente entre las semiosferas mexicana/americana y la fronteriza.
ContributorsEncinas, Diana (Author) / Volek, Emil (Committee member) / Hernández-G., Manuel De Jesús (Committee member) / Acereda, Alberto (Committee member) / Arizona State University (Publisher)
Created2011
Description
Parents die during the lives of their children. If the child is an adolescent, that death will impact the student's education immediately or in subsequent years. Findings show the death of a mother does impact the daughter's education. It is imperative educators are willing to work with the student at the time the death occurs as well as in the ensuing months. Seidman's (2006) three-interview format was used as a template for the interviews of 11 women, ranging in age from 19 to 78 and whose mothers died when the women were adolescents. The interviews were primarily conducted in one sitting, transcribed, and then analyzed for common themes that connected to the research on the topic. Those themes include grieving, the role of caring in education, the role of teacher as the second mother, mother-daughter relationships, and the impact of parent death on schooling. These themes from the data cross cut with thematic strands within the study's theoretical framework: the nurturing and empathetic role of the mother, a desire of the daughter not to be different, and the ethics of caring. Findings in this study reveal that the negative impacts of mother loss are felt in diffuse ways, such as a lack of academic or emotional encouragement. Many women discussed the need and availability of support groups including groups at colleges. One practical implication of these findings is schools need to become caring communities in which caring is the norm for all students and teachers, thereby providing all students with needed support in times of crisis. The implications for further research include the impact of the mother death on the education of daughters, how volunteering with an organization related to the cause of the mother's death assists the daughter and types of programs most important to a student's success in post-secondary education. Adolescents are in a time of great change in their lives, and for a daughter, the loss of a mother has an everlasting, life-changing impact.
ContributorsRatti, Theresa Helen McLuskey (Author) / Mccarty, Teresa L (Thesis advisor) / Fischman, Gustavo E. (Committee member) / Powers, Jeanne M. (Committee member) / Arizona State University (Publisher)
Created2011
Description
Currently Java is making its way into the embedded systems and mobile devices like androids. The programs written in Java are compiled into machine independent binary class byte codes. A Java Virtual Machine (JVM) executes these classes. The Java platform additionally specifies the Java Native Interface (JNI). JNI allows Java code that runs within a JVM to interoperate with applications or libraries that are written in other languages and compiled to the host CPU ISA. JNI plays an important role in embedded system as it provides a mechanism to interact with libraries specific to the platform. This thesis addresses the overhead incurred in the JNI due to reflection and serialization when objects are accessed on android based mobile devices. It provides techniques to reduce this overhead. It also provides an API to access objects through its reference through pinning its memory location. The Android emulator was used to evaluate the performance of these techniques and we observed that there was 5 - 10 % performance gain in the new Java Native Interface.
ContributorsChandrian, Preetham (Author) / Lee, Yann-Hang (Thesis advisor) / Davulcu, Hasan (Committee member) / Li, Baoxin (Committee member) / Arizona State University (Publisher)
Created2011
Description
Dietary self-monitoring has been shown to be a predictor of weight loss success and is a prevalent part of behavioral weight control programs. As more weight loss applications have become available on smartphones, this feasibility study investigated whether the use of a smartphone application, or a smartphone memo feature would improve dietary self-monitoring over the traditional paper-and-pencil method. The study also looked at whether the difference in methods would affect weight loss. Forty-seven adults (BMI 25 to 40 kg/m2) completed an 8-week study focused on tracking the difference in adherence to a self-monitoring protocol and subsequent weight loss. Participants owning iPhones (n=17) used the 'Lose It' application (AP) for diet and exercise tracking and were compared to smartphone participants who recorded dietary intake using a memo (ME) feature (n=15) on their phone and participants using the traditional paper-and-pencil (PA) method (n=15). There was no significant difference in completion rates between groups with an overall completion rate of 85.5%. The overall mean adherence to self-monitoring for the 8-week period was better in the AP group than the PA group (p = .024). No significant difference was found between the AP group and ME group (p = .148), or the ME group and the PA group (p = .457). Weight loss for the 8 week study was significant for all groups (p = .028). There was no significant difference in weight loss between groups. Number of days recorded regardless of group assignment showed a weak correlation to weight loss success (p = .068). Smartphone owners seeking to lose weight should be encouraged by the potential success associated with dietary tracking using a smartphone app as opposed to the traditional paper-and-pencil method.
ContributorsCunningham, Barbara (Author) / Wharton, Christopher (Christopher Mack), 1977- (Thesis advisor) / Johnston, Carol (Committee member) / Hall, Richard (Committee member) / Arizona State University (Publisher)
Created2012
Description
"White flight" is a sociological phenomenon where White members depart urban neighborhoods or schools predominantly populated by minorities, and move to places like suburbs or commuter towns. A huge limitation in White flight research does not account for communities in rural America. The rural community of Garden City, Kansas, is of particular interest because of its shift in demographics over the years. Garden City has transformed dramatically with the arrival of immigrants to staff meatpacking plants and their children who attend the Garden City Public School District. In the last eighteen years, the Garden City Public School District has experienced a 204% growth in Hispanic student enrollment while simultaneously experiencing a 54% decline in White student enrollment. The exodus of White students from the Garden City Public School District is the focus of this research. The findings of this study indicate that White flight exists in the Garden City Public School District primarily as a product of racism due to White community constituents' feelings of xenophobia and ethnophobia toward Garden City's minority populations.
ContributorsVolk, Michael J (Author) / Glass, Gene V (Thesis advisor) / Danzig, Arnold B. (Committee member) / Davey, Lynn M. (Committee member) / Arizona State University (Publisher)
Created2011
Description
Membrane proteins are very important for all living cells, being involved in respiration, photosynthesis, cellular uptake and signal transduction, amongst other vital functions. However, less than 300 unique membrane protein structures have been determined to date, often due to difficulties associated with the growth of sufficiently large and well-ordered crystals. This work has been focused on showing the first proof of concept for using membrane protein nanocrystals and microcrystals for high-resolution structure determination. Upon determining that crystals of the membrane protein Photosystem I, which is the largest and most complex membrane protein crystallized to date, exist with only a hundred unit cells with sizes of less than 200 nm on an edge, work was done to develop a technique that could exploit the growth of the Photosystem I nanocrystals and microcrystals. Femtosecond X-ray protein nanocrystallography was developed for use at the first high-energy X-ray free electron laser, the LCLS at SLAC National Accelerator Laboratory, in which a liquid jet would bring fully hydrated Photosystem I nanocrystals into the interaction region of the pulsed X-ray source. Diffraction patterns were recorded from millions of individual PSI nanocrystals and data from thousands of different, randomly oriented crystallites were integrated using Monte Carlo integration of the peak intensities. The short pulses ( 70 fs) provided by the LCLS allowed the possibility to collect the diffraction data before the onset of radiation damage, exploiting the diffract-before-destroy principle. At the initial experiments at the AMO beamline using 6.9- Å wavelength, Bragg peaks were recorded to 8.5- Å resolution, and an electron-density map was determined that did not show any effects of X-ray-induced radiation damage. Recently, femtosecond X-ray protein nanocrystallography experiments were done at the CXI beamline of the LCLS using 1.3- Å wavelength, and Bragg reflections were recorded to 3- Å resolution; the data are currently being processed. Many additional techniques still need to be developed to explore the femtosecond nanocrystallography technique for experimental phasing and time-resolved X-ray crystallography experiments. The first proof-of-principle results for the femtosecond nanocrystallography technique indicate the incredible potential of the technique to offer a new route to the structure determination of membrane proteins.
ContributorsHunter, Mark (Author) / Fromme, Petra (Thesis advisor) / Wolf, George (Committee member) / Levitus, Marcia (Committee member) / Arizona State University (Publisher)
Created2011
Description
An emerging body of literature suggests that humans likely have multiple threat avoidance systems that enable us to detect and avoid threats in our environment, such as disease threats and physical safety threats. These systems are presumed to be domain-specific, each handling one class of potential threats, and previous research generally supports this assumption. Previous research has not, however, directly tested the domain-specificity of disease avoidance and self-protection by showing that activating one threat management system does not lead to responses consistent only with a different threat management system. Here, the domain- specificity of the disease avoidance and self-protection systems is directly tested using the lexical decision task, a measure of stereotype accessibility, and the implicit association test. Results, although inconclusive, more strongly support a series of domain-specific threat management systems than a single, domain- general system
ContributorsAnderson, Uriah Steven (Author) / Kenrick, Douglas T. (Thesis advisor) / Shiota, Michelle N. (Committee member) / Neuberg, Steven L. (Committee member) / Becker, David V (Committee member) / Arizona State University (Publisher)
Created2011