6 resultados para Mixed protonic electronic conductors

em Digital Commons @ DU | University of Denver Research


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This mixed method study aimed to redress the gap in the literature on academic service-learning partnerships, especially in Eastern settings. It utilized Enos and Morton's (2003) theoretical framework to explore these partnerships at the American University in Cairo (AUC). Seventy-nine community partners, administrators, faculty members, and students from a diverse range of age, citizenship, racial, educational, and professional backgrounds participated in the study. Qualitative interviews were conducted with members of these four groups, and a survey with both close-ended and open-ended questions administered to students yielded 61 responses. Qualitative analyses revealed that the primary motivators for partners' engagement in service-learning partnerships included contributing to the community, enhancing students' learning and growth, and achieving the civic mission of the University. These partnerships were characterized by short-term relationships with partners' aspiring to progress toward long-term commitments. The challenges to these partnerships included issues pertaining to the institution, partnering organizations, culture, politics, pedagogy, students, and faculty members. Key strategies for improving these partnerships included institutionalizing service-learning in the University and cultivating an institutional culture supportive of community engagement. Quantitative analyses showed statistically significant relationships between students' scores on the Community Awareness and Interpersonal Effectiveness scales and their overall participation in community service activities inside and outside the classroom, as well as a statistically significant difference between their scores on the Community Awareness scale and department offering service-learning courses. The study's outcomes underscore the role of the local culture in shaping service-learning partnerships, as well as the role of both curricular and extracurricular activities in boosting students' awareness of their community and interpersonal effectiveness. Cultivating a culture of community engagement and building support mechanisms for engaged scholarship are among the critical steps required by public policy-makers in Egypt to promote service-learning in Egyptian higher education. Institutionalizing service-learning partnerships at AUC and enhancing the visibility of these partnerships on campus and in the community are essential to the future growth of these collaborations. Future studies should explore factors affecting community partners' satisfaction with these partnerships, top-down and bottom-up support to service-learning, the value of reflection to faculty members, and the influence of students' economic backgrounds on their involvement in service-learning partnerships.

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Development of transparent oxide semiconductors (TOS) from Earth-abundant materials is of great interest for cost-effective thin film device applications, such as solar cells, light emitting diodes (LEDs), touch-sensitive displays, electronic paper, and transparent thin film transistors. The need of inexpensive or high performance electrode might be even greater for organic photovoltaic (OPV), with the goal to harvest renewable energy with inexpensive, lightweight, and cost competitive materials. The natural abundance of zinc and the wide bandgap ($sim$3.3 eV) of its oxide make it an ideal candidate. In this dissertation, I have introduced various concepts on the modulations of various surface, interface and bulk opto-electronic properties of ZnO based semiconductor for charge transport, charge selectivity and optimal device performance. I have categorized transparent semiconductors into two sub groups depending upon their role in a device. Electrodes, usually 200 to 500 nm thick, optimized for good transparency and transporting the charges to the external circuit. Here, the electrical conductivity in parallel direction to thin film, i.e bulk conductivity is important. And contacts, usually 5 to 50 nm thick, are optimized in case of solar cells for providing charge selectivity and asymmetry to manipulate the built in field inside the device for charge separation and collection. Whereas in Organic LEDs (OLEDs), contacts provide optimum energy level alignment at organic oxide interface for improved charge injections. For an optimal solar cell performance, transparent electrodes are designed with maximum transparency in the region of interest to maximize the light to pass through to the absorber layer for photo-generation, plus they are designed for minimum sheet resistance for efficient charge collection and transport. As such there is need for material with high conductivity and transparency. Doping ZnO with some common elements such as B, Al, Ga, In, Ge, Si, and F result in n-type doping with increase in carriers resulting in high conductivity electrode, with better or comparable opto-electronic properties compared to current industry-standard indium tin oxide (ITO). Furthermore, improvement in mobility due to improvement on crystallographic structure also provide alternative path for high conductivity ZnO TCOs. Implementing these two aspects, various studies were done on gallium doped zinc oxide (GZO) transparent electrode, a very promising indium free electrode. The dynamics of the superimposed RF and DC power sputtering was utilized to improve the microstructure during the thin films growth, resulting in GZO electrode with conductivity greater than 4000 S/cm and transparency greater than 90 %. Similarly, various studies on research and development of Indium Zinc Tin Oxide and Indium Zinc Oxide thin films which can be applied to flexible substrates for next generation solar cells application is presented. In these new TCO systems, understanding the role of crystallographic structure ranging from poly-crystalline to amorphous phase and the influence on the charge transport and optical transparency as well as important surface passivation and surface charge transport properties. Implementation of these electrode based on ZnO on opto-electronics devices such as OLED and OPV is complicated due to chemical interaction over time with the organic layer or with ambient. The problem of inefficient charge collection/injection due to poor understanding of interface and/or bulk property of oxide electrode exists at several oxide-organic interfaces. The surface conductivity, the work function, the formation of dipoles and the band-bending at the interfacial sites can positively or negatively impact the device performance. Detailed characterization of the surface composition both before and after various chemicals treatment of various oxide electrode can therefore provide insight into optimization of device performance. Some of the work related to controlling the interfacial chemistry associated with charge transport of transparent electrodes are discussed. Thus, the role of various pre-treatment on poly-crystalline GZO electrode and amorphous indium zinc oxide (IZO) electrode is compared and contrasted. From the study, we have found that removal of defects and self passivating defects caused by accumulation of hydroxides in the surface of both poly-crystalline GZO and amorphous IZO, are critical for improving the surface conductivity and charge transport. Further insight on how these insulating and self-passivating defects cause charge accumulation and recombination in an device is discussed. With recent rapid development of bulk-heterojunction organic photovoltaics active materials, devices employing ZnO and ZnO based electrode provide air stable and cost-competitive alternatives to traditional inorganic photovoltaics. The organic light emitting diodes (OLEDs) have already been commercialized, thus to follow in the footsteps of this technology, OPV devices need further improvement in power conversion efficiency and stable materials resulting in long device lifetimes. Use of low work function metals such as Ca/Al in standard geometry do provide good electrode for electron collection, but serious problems using low work-function metal electrodes originates from the formation of non-conductive metal oxide due to oxidation resulting in rapid device failure. Hence, using low work-function, air stable, conductive metal oxides such as ZnO as electrons collecting electrode and high work-function, air stable metals such as silver for harvesting holes, has been on the rise. Devices with degenerately doped ZnO functioning as transparent conductive electrode, or as charge selective layer in a polymer/fullerene based heterojunction, present useful device structures for investigating the functional mechanisms within OPV devices and a possible pathway towards improved air-stable high efficiency devices. Furthermore, analysis of the physical properties of the ZnO layers with varying thickness, crystallographic structure, surface chemistry and grain size deposited via various techniques such as atomic layer deposition, sputtering and solution-processed ZnO with their respective OPV device performance is discussed. We find similarity and differences in electrode property for good charge injection in OLEDs and good charge collection in OPV devices very insightful in understanding physics behind device failures and successes. In general, self-passivating surface of amorphous TCOs IZO, ZTO and IZTO forms insulating layer that hinders the charge collection. Similarly, we find modulation of the carrier concentration and the mobility in electron transport layer, namely zinc oxide thin films, very important for optimizing device performance.

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High-Temperature Low-Sag (HTLS) high voltage overhead conductors offer higher operating temperatures, reduced resistance and less sag than conventional designs. With up to twice the current capacity for the same diameter conductor, they may help ease the power shortage in the constantly increasing electricity demand, but there might be some concerns about their corrosion resistance. These new conductors use materials relatively new to the power industry, such as advanced carbon fiber polymer matrix composites and unique metal matrix composites/nano-composites predominantly used in aerospace industries. This study has made an initial assessment of potential galvanic corrosion problems in three very different HTLS designs: ACCC (Aluminum Conductor Composite Core), ACCR (Aluminum Conductor Composite Reinforced) and ACSS (Aluminum Conductor Steel Supported). In particular the ACCC design was evaluated for its resistance to corrosion and compared to the other designs. The study concludes that all three designs can develop galvanic corrosion under certain circumstances. While the results are not sufficient to make service life predictions of any of the tested conductors, they point out the necessity of thorough corrosion testing of all new conductor designs.

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Non-suicidal self-injury (NSSI), such as cutting and burning, is a widespread social problem among lesbian, gay, bisexual, transgender, queer, and questioning (LGBTQ) youth. Extant research indicates that this population is more than twice as likely to engage in NSSI than heterosexual and cisgender (non-transgender) youth. Despite the scope of this social problem, it remains relatively unexamined in the literature. Research on other risk behaviors among LGBTQ youth indicates that experiencing homophobia and transphobia in key social contexts such as families, schools, and peer relationships contributes to health disparities among this group. Consequently, the aims of this study were to examine: (1) the relationship between LGBTQ youth's social environments and their NSSI behavior, and (2) whether/how specific aspects of the social environment contribute to an understanding of NSSI among LGBTQ youth. This study was conducted using an exploratory, sequential mixed methods design with two phases. The first phase of the study involved analysis of transcripts from interviews conducted with 44 LGBTQ youth recruited from a community-based organization. In this phase, five qualitative themes were identified: (1) Violence; (2) Misconceptions, Stigma, and Shame; (3) Negotiating LGBTQ Identity; (4) Invisibility and Isolation; and (5) Peer Relationships. Results from the qualitative phase were used to identify key variables and specify statistical models in the second, quantitative, phase of the study, using secondary data from a survey of 252 LGBTQ youth. The qualitative phase revealed how LGBTQ youth, themselves, described the role of the social environment in their NSSI behavior, while the quantitative phase was used to determine whether the qualitative findings could be used to predict engagement in NSSI among a larger sample of LGBTQ youth. The quantitative analyses found that certain social-environmental factors such as experiencing physical abuse at home, feeling unsafe at school, and greater openness about sexual orientation significantly predicted the likelihood of engaging in NSSI among LGBTQ youth. Furthermore, depression partially mediated the relationships between family physical abuse and NSSI and feeling unsafe at school and NSSI. The qualitative and quantitative results were compared in the interpretation phase to explore areas of convergence and incongruence. Overall, this study's findings indicate that social-environmental factors are salient to understanding NSSI among LGBTQ youth. The particular social contexts in which LGBTQ youth live significantly influence their engagement in this risk behavior. These findings can inform the development of culturally relevant NSSI interventions that address the social realities of LGBTQ youth's lives.

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Online education is a new teaching and learning medium with few current guidelines for faculty, administrators or students. Its rapid growth over the last decade has challenged academic institutions to keep up with the demand, while also providing a quality education. Our understanding of the factors that determine quality and effective online learning experiences that lead to student learning outcomes is still evolving. There is a lack of consensus on the effectiveness of online versus face-to-face education in the current research. The U.S. Department of Education conducted a meta-analysis in 2009 and concluded that student-learning outcomes in online courses were equal to and, often times, better than face-to-face traditional courses. Subsequent research has found contradictory findings, and further inquiry is necessary. The purpose of this embedded mixed methods design research study is to further our understanding of the factors that create quality and successful educational outcomes in an online course. To achieve this, the first phase of this study measured and compared learning outcomes in an online and in class graduate-level legal administration course. The second phase of the study entailed interviews with those students in both the online and face-to-face sections to understand their perspectives on the factors contributing to learning outcomes. Six themes emerged from the qualitative findings: convenience, higher order thinking, discussions, professor engagement, professor and student interaction, and face-to-face interaction. Findings from this study indicate the factors students perceive as contributing to learning outcomes in an online course are consistent among all students and are supported in the existing literature. Higher order thinking, however, emerged as a stronger theme than indicated in the current research, and the face-to-face nature of the traditional classroom may be more an issue of familiarity than a factor contributing to learning outcomes. As education continues to reach new heights and developments in technology advance, the factors found to contribute to student learning outcomes will be refined and enhanced. These developments will continue to transform the ways in which we deliver and receive knowledge in both traditional and online classrooms. While there is a growing body of research on online education, the field’s evolution has unsettled earlier findings and posed new areas to investigate.

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As world communication, technology, and trade become increasingly integrated through globalization, multinational corporations seek employees with global leadership experience and skills. However, the demand for these skills currently outweighs the supply. Given the rarity of globally ready leaders, global competency development should be emphasized in higher education programs. The reality, however, is that university graduate programs are often outdated and focus mostly on cognitive learning. Global leadership competence requires moving beyond the cognitive domain of learning to create socially responsible and culturally connected global leaders. This requires attention to development methods; however, limited research in global leadership development methods has been conducted. A new conceptual model, the global leadership development ecosystem, was introduced in this study to guide the design and evaluation of global leadership development programs. It was based on three theories of learning and was divided into four development methodologies. This study quantitatively tested the model and used it as a framework for an in-depth examination of the design of one International MBA program. The program was first benchmarked, by means of a qualitative best practices analysis, against the top-ranking IMBA programs in the world. Qualitative data from students, faculty, administrators, and staff was then examined, using descriptive and focused data coding. Quantitative data analysis, using PASW Statistics software, and a hierarchical regression, showed the individual effect of each of the four development methods, as well as their combined effect, on student scores on a global leadership assessment. The analysis revealed that each methodology played a distinct and important role in developing different competencies of global leadership. It also confirmed the critical link between self-efficacy and global leadership development.