Matching Items (43,917)
Description
Due to restructuring and open access to the transmission system, modern electric power systems are being operated closer to their operational limits. Additionally, the secure operational limits of modern power systems have become increasingly difficult to evaluate as the scale of the network and the number of transactions between utilities increase. To account for these challenges associated with the rapid expansion of electric power systems, dynamic equivalents have been widely applied for the purpose of reducing the computational effort of simulation-based transient security assessment. Dynamic equivalents are commonly developed using a coherency-based approach in which a retained area and an external area are first demarcated. Then the coherent generators in the external area are aggregated and replaced by equivalenced models, followed by network reduction and load aggregation. In this process, an improperly defined retained area can result in detrimental impacts on the effectiveness of the equivalents in preserving the dynamic characteristics of the original unreduced system. In this dissertation, a comprehensive approach has been proposed to determine an appropriate retained area boundary by including the critical generators in the external area that are tightly coupled with the initial retained area. Further-more, a systematic approach has also been investigated to efficiently predict the variation in generator slow coherency behavior when the system operating condition is subject to change. Based on this determination, the critical generators in the external area that are tightly coherent with the generators in the initial retained area are retained, resulting in a new retained area boundary. Finally, a novel hybrid dynamic equivalent, consisting of both a coherency-based equivalent and an artificial neural network (ANN)-based equivalent, has been proposed and analyzed. The ANN-based equivalent complements the coherency-based equivalent at all the retained area boundary buses, and it is designed to compensate for the discrepancy between the full system and the conventional coherency-based equivalent. The approaches developed have been validated on a large portion of the Western Electricity Coordinating Council (WECC) system and on a test case including a significant portion of the eastern interconnection.
Contributors
Ma, Feng (Author) / Vittal, Vijay (Thesis advisor) / Tylavsky, Daniel (Committee member) / Heydt, Gerald (Committee member) / Si, Jennie (Committee member) / Ayyanar, Raja (Committee member) / Arizona State University (Publisher)
Created
2011
Description
Semiconductor devices are generally analyzed with relatively simple equations or with detailed computer simulations. Most text-books use these simple equations and show device diagrams that are frequently very simplified and occasionally incorrect. For example, the carrier densities near the pinch-off point in MOSFETs and JFETs and the minority carrier density in the base near the reverse-biased base-collector junction are frequently assumed to be zero or near zero. Also the channel thickness at the pinch-off point is often shown to approach zero. None of these assumptions can be correct. The research in thesis addresses these points. I simulated the carrier densities, potentials, electric fields etc. of MOSFETs, BJTs and JFETs at and near the pinch-off regions to determine exactly what happens there. I also simulated the behavior of the quasi-Fermi levels. For MOSFETs, the channel thickness expands slightly before the pinch-off point and then spreads out quickly in a triangular shape and the space-charge region under the channel actually shrinks as the potential increases from source to drain. For BJTs, with collector-base junction reverse biased, most minority carriers diffuse through the base from emitter to collector very fast, but the minority carrier concentration at the collector-base space-charge region is not zero. For JFETs, the boundaries of the space-charge region are difficult to determine, the channel does not disappear after pinch off, the shape of channel is always tapered, and the carrier concentration in the channel decreases progressively. After simulating traditional sized devices, I also simulated typical nano-scaled devices and show that they behave similarly to large devices. These simulation results provide a more complete understanding of device physics and device operation in those regions usually not addressed in semiconductor device physics books.
Contributors
Yang, Xuan (Author) / Schroder, Dieter K. (Thesis advisor) / Vasileska, Dragica (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created
2011
Contributors
Han, Sarah (Performer) / Kim, Hyewon Rina (Performer) / Chen, Neilson (Performer) / ASU Library. Music Library (Contributor)
Created
2018-04-07
Description
Effectively educating students with autism is a necessary element in providing all students with a free and appropriate public education, and as the number of students diagnosed with an autism spectrum disorder continues to increase in both public and private educational settings, providing successful and satisfactory professional development opportunities in the area of autism is becoming increasingly essential. This study explored the experiences of twenty-three educators in a suburban southwest K-12 public school district, as they participated in a fifteen-hour professional development course in an online or face-to-face format, and collaboratively problem-solved their challenges in educating students with autism. Qualitative data was collected from participants' weekly written reflections and comments from a pre- and post-survey on attitudes, to determine quality of and satisfaction with collaboration in relation to course format. Results indicated that the online format produced higher-quality collaboration when it came to presenting one's own situation(s) to the group, finding group discussions helpful, having enough time to collaborate, providing feedback/suggestions to group members, and perceiving suggestions for one's own situation as helpful (as evidenced by the number of suggestions that participants said they would likely implement). The face-to-face format produced higher-quality collaboration when it came to in-depth problem-solving regarding a situation, implementing suggestions for one's own situation, and relating course content to collaborative activities. Participants' attitudes about using technology as a means of collaboration showed little change overall from pre- to post-survey. Though slight increases in positive attitudes concerning technology were found in various areas, many participants still thought highly of a face-to-face format for collaborative purposes, even after participating in the online professional development course. Findings may be of use to educational institutions developing online or face-to-face professional development opportunities in the area of autism.
Contributors
Wozniak, Renee M (Author) / McCoy, Kathleen M. (Thesis advisor) / Puckett, Kathleen (Committee member) / Gehrke, Rebecca (Committee member) / Arizona State University (Publisher)
Created
2011
Description
This thesis focuses on the theoretical work done to determine thermodynamic properties of a chalcopyrite thin-film material for use as a photovoltaic material in a tandem device. The material of main focus here is ZnGeAs2, which was chosen for the relative abundance of constituents, favorable photovoltaic properties, and good lattice matching with ZnSnP2, the other component in this tandem device. This work is divided into two main chapters, which will cover: calculations and method to determine the formation energy and abundance of native point defects, and a model to calculate the vapor pressure over a ternary material from first-principles. The purpose of this work is to guide experimental work being done in tandem to synthesize ZnGeAs2 in thin-film form with high enough quality such that it can be used as a photovoltaic. Since properties of photovoltaic depend greatly on defect concentrations and film quality, a theoretical understanding of how laboratory conditions affect these properties is very valuable. The work done here is from first-principles and utilizes density functional theory using the local density approximation. Results from the native point defect study show that the zinc vacancy (VZn) and the germanium antisite (GeZn) are the more prominent defects; which most likely produce non-stoichiometric films. The vapor pressure model for a ternary system is validated using known vapor pressure for monatomic and binary test systems. With a valid ternary system vapor pressure model, results show there is a kinetic barrier to decomposition for ZnGeAs2.
Contributors
Tucker, Jon R (Author) / Van Schilfgaarde, Mark (Thesis advisor) / Newman, Nathan (Committee member) / Adams, James (Committee member) / Arizona State University (Publisher)
Created
2011
Description
Proportional-Integral-Derivative (PID) controllers are a versatile category of controllers that are commonly used in the industry as control systems due to the ease of their implementation and low cost. One problem that continues to intrigue control designers is the matter of finding a good combination of the three parameters - P, I and D of these controllers so that system stability and optimum performance is achieved. Also, a certain amount of robustness to the process is expected from the PID controllers. In the past, many different methods for tuning PID parameters have been developed. Some notable techniques are the Ziegler-Nichols, Cohen-Coon, Astrom methods etc. For all these techniques, a simple limitation remained with the fact that for a particular system, there can be only one set of tuned parameters; i.e. there are no degrees of freedom involved to readjust the parameters for a given system to achieve, for instance, higher bandwidth. Another limitation in most cases is where a controller is designed in continuous time then converted into discrete-time for computer implementation. The drawback of this method is that some robustness due to phase and gain margin is lost in the process. In this work a method of tuning PID controllers using a loop-shaping approach has been developed where the bandwidth of the system can be chosen within an acceptable range. The loop-shaping is done against a Glover-McFarlane type ℋ∞ controller which is widely accepted as a robust control design method. The numerical computations are carried out entirely in discrete-time so there is no loss of robustness due to conversion and approximations near Nyquist frequencies. Some extra degrees of freedom owing to choice of bandwidth and capability of choosing loop-shapes are also involved and are discussed in detail. Finally, comparisons of this method against existing techniques for tuning PID controllers both in continuous and in discrete-time are shown. The results tell us that our design performs well for loop-shapes that are achievable through a PID controller.
Contributors
Shafique, Md. Ashfaque Bin (Author) / Tsakalis, Konstantinos S. (Thesis advisor) / Rodriguez, Armando A. (Committee member) / Si, Jennie (Committee member) / Arizona State University (Publisher)
Created
2011
Description
The current study is a follow up to a previous evaluation of Believe It!, an internet-based career development program for adolescent girls. This study attempted to extend the program's effectiveness by manipulating animated agent appearance based on literature suggesting that agent appearance has implications for human-computer program interface. Participants included 52 Latinas (ages 11 to 14) randomly assigned to view one of two versions of the revised career program. Each version contained identical content but included animated agents designed to represent different ethnicities. Pre and post-treatment scores for three career belief measures and an occupational stereotype measure were analyzed using a MANCOVA. The results were not significant and further analyses revealed that the results were confounded by complications with the perceived ethnicity of the animated agents. Despite a lack of significance the results provide enriching information about Latina adolescent perception of ethnicity.
Contributors
Hardy, Amanda (Author) / Horan, John (Thesis advisor) / Atkinson, Robert (Committee member) / Homer, Judith (Committee member) / Arizona State University (Publisher)
Created
2011
Description
This dissertation examines Japanese preschool teachers' cultural practices and beliefs about the pedagogy of social-emotional development. The study is an interview-based, ethnographic study, which is based on the video-cued mutivocal ethnographic method. This study focuses on the emic terms that Japanese preschool teachers use to explain their practices, such as amae (dependency), omoiyari (empathy), sabishii (loneliness), mimamoru (watching and waiting) and garari (peripheral participation). My analysis suggests that sabishii, amae, and omoiyari form a triad of emotional exchange that has a particular cultural patterning and salience in Japan and in the Japanese approach to the socialization of emotions in early childhood. Japanese teachers think about the development of the class as a community, which is different from individual-centric Western pedagogical perspective that gives more attention to each child's development. Mimamoru is a pedagogical philosophy and practice in Japanese early childhood education. A key component of Japanese teachers' cultural practices and beliefs about the pedagogy of social-emotional development is that the process requires the development not only of children as individuals, but also of children in a preschool class as a community. In addition, the study suggests that at a deeper level these emic concepts reflect more general Japanese cultural notions of time, space, sight, and body. This dissertation concludes with the argument that teachers' implicit cultural practices and beliefs is "A cultural art of teaching." Teachers' implicit cultural practices and beliefs are harmonized in the teachers' mind and body, making connections between them, and used depending on the nuances of a situation, as informed by teachers' conscious and unconscious thoughts. The study has also shown evidence of similar practices and logic vertically distributed within Japanese early childhood education, from the way teachers act with children, to the way directors act with teachers, to the way government ministries act with directors, to the way deaf and hearing educators act with their deaf and hearing students. Because these practices are forms of bodily habitus and implicit Japanese culture, it makes sense that they are found across fields of action.
Contributors
Hayashi, Akiko (Author) / Tobin, Joseph (Thesis advisor) / Eisenberg, Nancy (Committee member) / Nakagawa, Kathryn (Committee member) / Fischman, Gustavo (Committee member) / Swadener, Elizabeth (Committee member) / Arizona State University (Publisher)
Created
2011
Description
This thesis analyzes how several well-known biographies of popular nineteenth-century British literary figures overturned and upset the usual heroic literary biographies that typified the genre during the Victorian era. Popular public opinion in the nineteenth century was that literary biographies existed as moral guideposts--designed to instruct and edify readers. Richard D. Altick's theory of biographical conventions of reticence--which contends that ultimately literary biographies were committed to establishing or preserving an idealized image of the author--is utilized to explore the nuances of how certain radical biographies in which the biographer is forthright about the subject's private life displeased and disturbed the public. In order to illustrate this study's central argument, several literary biographies that were considered among the most radical of the late Victorian period--John Forster's Life of Charles Dickens, James Anthony Froude's Life of Carlyle, Mathilde Blind's George Eliot, and John Cordy Jeaffreson's The Real Shelley--are analyzed as case studies. These biographies of writers' lives made heroic figures appear human, vulnerable, petty, et cetera by exposing private life matters in a public biography--something that was not done in an age that called for discreet biographies of its literary icons. Victorian periodicals such as magazines and newspapers assist in ascertaining just how the British public reacted to these biographies, and the ramifications they possessed for worshipping literary idols. Additionally explored are the implications that candid literary biographies had for Victorian author-worship and the role of literature, authors, and biography in British society. This study concludes with a discussion of the implications that these candid literary biographies had into the early twentieth century with the publication of Lytton Strachey's "deflated" biography, Eminent Victorians, published in 1918, and summarizes overall findings and conclusions.
Contributors
LeTourneur-Johnson, Jessica Ann (Author) / Warren-Findley, Jannelle (Thesis advisor) / Codell, Julie F. (Committee member) / Szuter, Christine (Committee member) / Arizona State University (Publisher)
Created
2011
Description
The nucleon resonance spectrum consists of many overlapping excitations. Polarization observables are an important tool for understanding and clarifying these spectra. While there is a large data base of differential cross sections for the process, very few data exist for polarization observables. A program of double polarization experiments has been conducted at Jefferson Lab using a tagged polarized photon beam and a frozen spin polarized target (FROST). The results presented here were taken during the first running period of FROST using the CLAS detector at Jefferson Lab with photon energies ranging from 329 MeV to 2.35 GeV. Data are presented for the E polarization observable for eta meson photoproduction on the proton from threshold (W=1500 MeV) to W=1900 MeV. Comparisons to the partial wave analyses of SAID and Bonn-Gatchina along with the isobar analysis of eta-MAID are made. These results will help distinguish between current theoretical predictions and refine future theories.
Contributors
Morrison, Brian (Author) / Ritchie, Barry (Thesis advisor) / Dugger, Michael (Committee member) / Shovkovy, Igor (Committee member) / Davies, Paul (Committee member) / Alarcon, Ricardo (Committee member) / Arizona State University (Publisher)
Created
2011