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- All Subjects: Materials Science
- Genre: Doctoral Dissertation
- Genre: Masters Thesis
Description
Metal hydride materials have been intensively studied for hydrogen storage applications. In addition to potential hydrogen economy applications, metal hydrides offer a wide variety of other interesting properties. For example, hydrogen-dominant materials, which are hydrides with the highest hydrogen content for a particular metal/semimetal composition, are predicted to display high-temperature superconductivity. On the other side of the spectrum are hydrides with small amounts of hydrogen (0.1 - 1 at.%) that are investigated as viable magnetic, thermoelectric or semiconducting materials. Research of metal hydride materials is generally important to gain fundamental understanding of metal-hydrogen interactions in materials. Hydrogenation of Zintl phases, which are defined as compounds between an active metal (alkali, alkaline earth, rare earth) and a p-block metal/semimetal, were attempted by a hot sintering method utilizing an autoclave loaded with gaseous hydrogen (< 9 MPa). Hydride formation competes with oxidative decomposition of a Zintl phase. The oxidative decomposition, which leads to a mixture of binary active metal hydride and p-block element, was observed for investigated aluminum (Al) and gallium (Ga) containing Zintl phases. However, a new phase Li2Al was discovered when Zintl phase precursors were synthesized. Using the single crystal x-ray diffraction (SCXRD), the Li2Al was found to crystallize in an orthorhombic unit cell (Cmcm) with the lattice parameters a = 4.6404(8) Å, b = 9.719(2) Å, and c = 4.4764(8) Å. Increased demand for materials with improved properties necessitates the exploration of alternative synthesis methods. Conventional metal hydride synthesis methods, like ball-milling and autoclave technique, are not responding to the demands of finding new materials. A viable alternative synthesis method is the application of high pressure for the preparation of hydrogen-dominant materials. Extreme pressures in the gigapascal ranges can open access to new metal hydrides with novel structures and properties, because of the drastically increased chemical potential of hydrogen. Pressures up to 10 GPa can be easily achieved using the multi-anvil (MA) hydrogenations while maintaining sufficient sample volume for structure and property characterization. Gigapascal MA hydrogenations using ammonia borane (BH3NH3) as an internal hydrogen source were employed in the search for new hydrogen-dominant materials. Ammonia borane has high gravimetric volume of hydrogen, and additionally the thermally activated decomposition at high pressures lead to a complete hydrogen release at reasonably low temperature. These properties make ammonia borane a desired hydrogen source material. The missing member Li2PtH6 of the series of A2PtH6 compounds (A = Na to Cs) was accessed by employing MA technique. As the known heavier analogs, the Li2PtH6 also crystallizes in a cubic K2PtCl6-type structure with a cell edge length of 6.7681(3) Å. Further gigapascal hydrogenations afforded the compounds K2SiH6 and Rb2SiH6 which are isostructural to Li2PtH6. The cubic K2SiH6 and Rb2SiH6 are built from unique hypervalent SiH62- entities with the lattice parameters of 7.8425(9) and 8.1572(4) Å, respectively. Spectroscopic analysis of hexasilicides confirmed the presence of hypervalent bonding. The Si-H stretching frequencies at 1550 cm-1 appeared considerably decreased in comparison with a normal-valent (2e2c) Si-H stretching frequencies in SiH4 at around 2200 cm-1. However, the observed stretching modes in hypervalent hexasilicides were in a reasonable agreement with Ph3SiH2- (1520 cm-1) where the hydrogen has the axial (3e4c bonded) position in the trigoal bipyramidal environment.
ContributorsPuhakainen, Kati (Author) / Häussermann, Ulrich (Thesis advisor) / Seo, Dong (Thesis advisor) / Kouvetakis, John (Committee member) / Wolf, George (Committee member) / Arizona State University (Publisher)
Created2013
Description
Communication skills within dating contexts are developed during the adolescent years, and are associated with a lifelong ability to have satisfying, enduring, and non-violent partnerships. As such, they are currently and increasingly implemented into both more general forms of healthy relationship education, as well as that targeting the prevention of teen dating violence specifically. Reaching Mexican American youth with culturally and developmentally appropriate relationship education, including communication skills, may be particularly important given their earlier transitions to marital and parenting relationships, acculturative stressors that present them with unique coupling challenges, and their higher rates of teen dating violence as compared to European American youth. We know very little about how Mexican American dating couples communicate about areas of conflict. This dissertation research utilizes Bell and Naugle's (2008) framework of interpersonal violence to explore how cultural and developmental considerations may be integrated in order to better understand how communication behaviors contribute to Mexican American middle adolescents' experiences with dating conflict. I use an observational study design in order to 1.) Qualitatively explore the communication strategies used by a sample of committed couples, including integration of culturally- and developmentally-relevant contexts, 2.) Quantitatively examine whether couple-level discrepancies in acculturation are associated with observed negativity, including whether this relationship may be mediated by dissimilar gender-related beliefs, and to 3.) Review empirical findings pertaining to the communication behaviors of Mexican American adolescents and to integrate ecodevelopmental theory in said framework as informed by Papers 1, 2, and literature specific to this topic area. The ultimate aim of this dissertation research is to generate findings that may improve the dating health of Mexican American adolescents living in the United States.
ContributorsAdams, Heidi (Author) / Rankin Williams, Lela (Thesis advisor) / Marsiglia, Flavio (Committee member) / Anthony, Elizabeth (Committee member) / Arizona State University (Publisher)
Created2013
Description
Topological insulators with conducting surface states yet insulating bulk states have generated a lot of interest amongst the physics community due to their varied characteristics and possible applications. Doped topological insulators have presented newer physical states of matter where topological order co&ndashexists; with other physical properties (like magnetic order). The electronic states of these materials are very intriguing and pose problems and the possible solutions to understanding their unique behaviors. In this work, we use Electron Energy Loss Spectroscopy (EELS) – an analytical TEM tool to study both core&ndashlevel; and valence&ndashlevel; excitations in Bi2Se3 and Cu(doped)Bi2Se3 topological insulators. We use this technique to retrieve information on the valence, bonding nature, co-ordination and lattice site occupancy of the undoped and the doped systems. Using the reference materials Cu(I)Se and Cu(II)Se we try to compare and understand the nature of doping that copper assumes in the lattice. And lastly we utilize the state of the art monochromated Nion UltraSTEM 100 to study electronic/vibrational excitations at a record energy resolution from sub-nm regions in the sample.
ContributorsSubramanian, Ganesh (Author) / Spence, John (Thesis advisor) / Jiang, Nan (Committee member) / Chen, Tingyong (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2013
Description
This dissertation explores vulnerability to extreme heat hazards in the Maricopa County, Arizona metropolitan region. By engaging an interdisciplinary approach, I uncover the epidemiological, historical-geographical, and mitigation dimensions of human vulnerability to extreme heat in a rapidly urbanizing region characterized by an intense urban heat island and summertime heat waves. I first frame the overall research within global climate change and hazards vulnerability research literature, and then present three case studies. I conclude with a synthesis of the findings and lessons learned from my interdisciplinary approach using an urban political ecology framework. In the first case study I construct and map a predictive index of sensitivity to heat health risks for neighborhoods, compare predicted neighborhood sensitivity to heat-related hospitalization rates, and estimate relative risk of hospitalizations for neighborhoods. In the second case study, I unpack the history and geography of land use/land cover change, urban development and marginalization of minorities that created the metropolitan region's urban heat island and consequently, the present conditions of extreme heat exposure and vulnerability in the urban core. The third study uses computational microclimate modeling to evaluate the potential of a vegetation-based intervention for mitigating extreme heat in an urban core neighborhood. Several findings relevant to extreme heat vulnerability emerge from the case studies. First, two main socio-demographic groups are found to be at higher risk for heat illness: low-income minorities in sparsely-vegetated neighborhoods in the urban core, and the elderly and socially-isolated in the expansive suburban fringe of Maricopa County. The second case study reveals that current conditions of heat exposure in the region's urban heat island are the legacy of historical marginalization of minorities and large-scale land-use/land cover transformations of natural desert land covers into heat-retaining urban surfaces of the built environment. Third, summertime air temperature reductions in the range 0.9-1.9 °C and of up to 8.4 °C in surface temperatures in the urban core can be achieved through desert-adapted canopied vegetation, suggesting that, at the microscale, the urban heat island can be mitigated by creating vegetated park cool islands. A synthesis of the three case studies using the urban political ecology framework argues that climate changed-induced heat hazards in cities must be problematized within the socio-ecological transformations that produce and reproduce urban landscapes of risk. The interdisciplinary approach to heat hazards in this dissertation advances understanding of the social and ecological drivers of extreme heat by drawing on multiple theories and methods from sociology, urban and Marxist geography, microclimatology, spatial epidemiology, environmental history, political economy and urban political ecology.
ContributorsDeclet-Barreto, Juan (Author) / Harlan, Sharon L (Thesis advisor) / Bolin, Bob (Thesis advisor) / Hirt, Paul (Committee member) / Boone, Christopher (Committee member) / Arizona State University (Publisher)
Created2013
Community-based development: scaling up the correct use of misoprostol at home births in Afghanistan
Description
Globally, more than 350 000 women die annually from complications during pregnancy and childbirth (UNFPA, 2011). Nearly 99% of these, according to World Health Organization (WHO) trends (2010) occur in the developing world outside of a hospital setting with limited resources including emergency care (WHO, 2012; UNFPA, 2011). The most prevalent cause of death is postpartum hemorrhage (PPH), accounting for 25% of deaths according to WHO statistics (2012). Conditions in Afghanistan are reflective of the scope and magnitude of the problem. In Afghanistan, maternal mortality is thought to be among the highest in the world. The Afghan Mortality Survey (AMS) data implies that one Afghan woman dies about every 2 hours from pregnancy-related causes (AMS, 2010). Lack of empowerment, education and access to health care resources increase a woman's risk of dying during pregnancy (AMS, 2010). This project aims to investigate the prospects of scaling-up the correct use of misoprostol, a prostaglandin E1 analogue, to treat PPH in developing countries where skilled assistance and resources are scant. As there has been little published on the lessons learned from programs already in place, this study is experience-driven, based on the knowledge of industry experts. This study employs a concurrent triangulation approach to synthesize quantitative data obtained from previous studies with qualitative information gathered through the testimonies of key personnel who participated in pilot programs involving misoprostol. There are many obstacles to scaling-up training initiatives in Afghanistan and other low-resource areas. The analysis concludes that the most crucial factors for scaling-up community-based programs include: more studies analyzing lessons learns from community driven approaches; stronger partnerships with community health care workers; overcoming barriers like association with abortion, misuse and product issues; and a heightened global and community awareness of the severity of PPH without treatment. These results have implications for those who actively work in Afghanistan to promote maternal health and other countries that may use Afghanistan's work as a blueprint for reducing maternal mortality through community-based approaches. Keywords: Afghanistan, community-based interventions, community-driven, maternal mortality, MDG5, misoprostol, postpartum hemorrhage, reproduction, scale-up
ContributorsCristy, Candice (Author) / Grossman, Gary (Thesis advisor) / Parmentier, Mary-Jane (Committee member) / Byrd, Denise (Committee member) / Arizona State University (Publisher)
Created2013
Description
The alkali activation of aluminosilicate materials as binder systems derived from industrial byproducts have been extensively studied due to the advantages they offer in terms enhanced material properties, while increasing sustainability by the reuse of industrial waste and byproducts and reducing the adverse impacts of OPC production. Fly ash and ground granulated blast furnace slag are commonly used for their content of soluble silica and aluminate species that can undergo dissolution, polymerization with the alkali, condensation on particle surfaces and solidification. The following topics are the focus of this thesis: (i) the use of microwave assisted thermal processing, in addition to heat-curing as a means of alkali activation and (ii) the relative effects of alkali cations (K or Na) in the activator (powder activators) on the mechanical properties and chemical structure of these systems. Unsuitable curing conditions instigate carbonation, which in turn lowers the pH of the system causing significant reductions in the rate of fly ash activation and mechanical strength development. This study explores the effects of sealing the samples during the curing process, which effectively traps the free water in the system, and allows for increased aluminosilicate activation. The use of microwave-curing in lieu of thermal-curing is also studied in order to reduce energy consumption and for its ability to provide fast volumetric heating. Potassium-based powder activators dry blended into the slag binder system is shown to be effective in obtaining very high compressive strengths under moist curing conditions (greater than 70 MPa), whereas sodium-based powder activation is much weaker (around 25 MPa). Compressive strength decreases when fly ash is introduced into the system. Isothermal calorimetry is used to evaluate the early hydration process, and to understand the reaction kinetics of the alkali powder activated systems. A qualitative evidence of the alkali-hydroxide concentration of the paste pore solution through the use of electrical conductivity measurements is also presented, with the results indicating the ion concentration of alkali is more prevalent in the pore solution of potassium-based systems. The use of advanced spectroscopic and thermal analysis techniques to distinguish the influence of studied parameters is also discussed.
ContributorsChowdhury, Ussala (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramanium D. (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2013
Description
This phenomenological qualitative study examines the experiences of volunteer tourism on host communities using social representations theory. The experiences of three stakeholder-groups (community residents, volunteers, and nongovernmental organizations) are considered. Overall objectives of this project are to investigate the following questions: a) what are the effects of volunteer tourism on a community as perceived by different stakeholders; b) what effects do volunteer tourists have on the community compared to other forms of tourism as perceived by different stakeholders; c) how do the various stakeholders perceive the different forms of tourism in communities in which they live or work; and d) why and how do nongovernmental organizations (NGOs) use volunteer tourism as a strategy for their projects. This study attempts to describe and interpret these meanings with a high degree of depth and richness using interviews, observation, and document analysis. Each chapter is written as a stand-alone paper to be published in a journal and describes the perspectives of the three groups interviewed with the final chapter a summary and comparison from all three groups. Findings show that there are both positive and negative impacts of volunteer tourism in favela communities, with the majority of the three groups expressing its positives and its importance to the community. All groups mentioned similar positive and negative elements of volunteer tourism with some elements that were unique to each group. This study also attempted to compare and contrast the differences between volunteer tourism and favela tours. The findings show that volunteer tourism helps recreate the social representations of the favela thereby improving self-esteem in the community, helps breakdown preconceptions, and helps create community pride. The community feels as equals with the volunteers and describes the interactions as friendships, sharing cultural experiences, and exchanging of knowledge. Conversely, all three groups described favela tours as dehumanizing using words like `safari tour' or `zoo tour' and felt that their community was being sold as a commodity. However, the interviews showed that all three groups, although had strong opinions about the ethical implications of favela tours, still felt conflicted when comparing it with some of the potential social and economic benefits that it may bring.
ContributorsAquino, Jessica Faustini (Author) / Andereck, Kathleen (Thesis advisor) / Mcgehee, Nancy (Committee member) / Phillips, Rhonda (Committee member) / Wang, Lili (Committee member) / Arizona State University (Publisher)
Created2013
Description
There is a popular notion that creativity is highly valued in our culture. However, those "in the trenches," people in creative endeavors that actually produce the acts of creativity, say this is not so. There is a negative correlation between the value stated and the true value placed on creativity by our contemporary culture. The primary purpose of this study was to investigate that correlation as well as a possible contributing factor to this negative correlation--the fear of risk involved in enacting and accepting creativity. The methods used in this study were literature review and interview. An extensive literature review was done, as much has been written on creativity. The review was done in four parts: 1) the difficulty in defining creativity; 2) fear and the fear of creativity; 3) solutions - ways to be, express, and accept creativity; and 4) the plethora of articles written about creativity. Six one-on-one interviews were conducted with creative individuals from a variety of commercial creative endeavors. Creatives in commercial fields were chosen specifically because of their ability to influence the culture. The results of this study showed that the hypothesis, that there is a negative correlation between the value stated and the true value placed on creativity, is true. The fear of risk involved in enacting and accepting creativity as a factor in this dichotomy was also shown to be true.
ContributorsGelman, Howard P (Author) / Heywood, Wil (Thesis advisor) / Patel, Mookesh (Committee member) / Knox, Gordon (Committee member) / Arizona State University (Publisher)
Created2013
Description
This study was done in collaboration with the Kino Border Initiative. The Kino Border Initiative is a Catholic, bi-national organization run by Missionary Sisters of the Eucharist, Jesuit priests and lay people. The organization is dedicated to providing services to recently deported migrants and migrants-in-transit through their soup kitchen, women's shelter and first aid station in Nogales, Sonora. Based on their experiences in the women's shelter, the Missionary Sisters of the Eucharist and researcher sought out to further understand migrant women's experiences of gender-based violence prior to migration. Using data collected by the Sisters, it was decided to use an analysis rooted in testimonio, and, in this way, use the women's words as a foundational basis for understanding the migration of women. The analysis is based on 62 testimonies related to women's histories of violence and their migration experiences, and the information from 74 intake questionnaires that were all analyzed retroactively. The analysis of data and testimonios has led to the realization that violence suffered by migrant women is not limited to the journey itself, and that 71% of women report having suffered some sort of violence either prior to or during migration. Often times, the first experiences of violence originated in their homes when they were children and continue to repeat itself throughout their lifetimes in varied forms. Their stories reveal how the decision to migrate is a consequence to the transnational and structural violence that pushes women to seek out ways to survive and provide for their families.
ContributorsConrad, Marla (Author) / Elenes, C. Alejandra (Thesis advisor) / Simmons, William P. (Committee member) / Téllez, Michelle (Committee member) / Arizona State University (Publisher)
Created2013
Description
The thesis studies new methods to fabricate optoelectronic Ge1-ySny/Si(100) alloys and investigate their photoluminescence (PL) properties for possible applications in Si-based photonics including IR lasers. The work initially investigated the origin of the difference between the PL spectrum of bulk Ge, dominated by indirect gap emission, and the PL spectrum of Ge-on-Si films, dominated by direct gap emission. It was found that the difference is due to the supression of self-absorption effects in Ge films, combined with a deviation from quasi-equilibrium conditions in the conduction band of undoped films. The latter is confirmed by a model suggesting that the deviation is caused by the shorter recombination lifetime in the films relative to bulk Ge. The knowledge acquired from this work was then utilized to study the PL properties of n-type Ge1-ySny/Si (y=0.004-0.04) samples grown via chemical vapor deposition of Ge2H6/SnD4/P(GeH3)3. It was found that the emission intensity (I) of these samples is at least 10x stronger than observed in un-doped counterparts and that the Idir/Iind ratio of direct over indirect gap emission increases for high-Sn contents due to the reduced gamma-L valley separation, as expected. Next the PL investigation was expanded to samples with y=0.05-0.09 grown via a new method using the more reactive Ge3H8 in place of Ge2H6. Optical quality, 1-um thick Ge1-ySny/Si(100) layers were produced using Ge3H10/SnD4 and found to exhibit strong, tunable PL near the threshold of the direct-indirect bandgap crossover. A byproduct of this study was the development of an enhanced process to produce Ge3H8, Ge4H10, and Ge5H12 analogs for application in ultra-low temperature deposition of Group-IV semiconductors. The thesis also studies synthesis routes of an entirely new class of semiconductor compounds and alloys described by Si5-2y(III-V)y (III=Al, V= As, P) comprising of specifically designed diamond-like structures based on a Si parent lattice incorporating isolated III-V units. The common theme of the two thesis topics is the development of new mono-crystalline materials on ubiquitous silicon platforms with the objective of enhancing the optoelectronic performance of Si and Ge semiconductors, potentially leading to the design of next generation optical devices including lasers, detectors and solar cells.
ContributorsGrzybowski, Gordon (Author) / Kouvetakis, John (Thesis advisor) / Chizmeshya, Andrew (Committee member) / Menéndez, Jose (Committee member) / Arizona State University (Publisher)
Created2013