Modeling and analysis for control of reactant and water distributions in fuel cells

McCain, Buz A University of Michigan 2008 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

It is shown that the critical task of controlling the water accumulation within the gas diffusion layers (GDL) and channels of a polymer electrolyte membrane fuel cell (PEMFC) benefits from a partial differential equation (PDE) approach. Starting from first principles, a fuel cell model is represented as a boundary value problem for a set of six coupled, nonlinear, second-order PDEs for mass transport across the gas diffusion layer, from channel-to-channel. The multi-input, multi-output model includes nonlinearities related to both switching and PDEs with polynomial coefficients in the dependent variable. The six PDEs are approximated, with justification founded in linear systems theory and a time-scale decomposition approach, by a semi-analytic solution (SAS) model that, compared to the full numeric solution, requires only one-third the number of states to be numerically integrated. This model simplification plays a critical role in the fundamental goal of the research, which is to provide a control-oriented model that maintains the meanings of the states in order to apply physically intuitive control algorithms. The SAS model consists of a set of numeric transient, analytic transient, and analytic steady-state solutions to the system of PDEs. Model accuracy is verified by comparison to the experimental voltage transient response from a 24-cell stack, and to the predictive capability of the full-order numeric model. The SAS model predicts degradation due to liquid water accumulation and voltage variations due to changes in inputs such as stack current, reactant excess ratio, and overall stack temperature with negligible variation versus the full-order model. The SAS model is created for application to real-time automatic control of spatial and temporal water and reactant distributions within a PEMFC. The semi-analytic solution is analyzed for open-loop stability and to gain insight into the physics of the equilibrium water distributions. Candidate distributions for vapor and liquid water are then identified which allow maximum membrane hydration while simultaneously avoiding voltage degradation that results from anode liquid water accumulation (flooding). The desired distributions would be maintained via control of the channel conditions (boundary value control) with the ultimate goal to maximize hydrogen utilization and prolong fuel cell life.

A qualitative study of pre-service teachers using co-teaching as a method to understand scientific process skills to teach inquiry

McCain, Jennifer Carter West Virginia University 2005 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The National Science Education Standards (NSES) have established scientific literacy as a goal for all students. The goals advocate scientific inquiry as an instructional strategy to be used in the classroom, and standards of inquiry have even been established. At the same time, co-teaching has become prevalent in classroom as regular education teachers work with special education teachers. The classrooms are inclusive and both teachers are to work together to benefit all the students. Research has shown positive perceptions and negative perceptions of co-teaching. In this study, pre-service teachers are co-taught an elementary science methods course at a medium-sized university. They are co-taught the basic science process skills by two science education instructors. In turn, they teach lessons to the methods course with a co-teaching partner covering the basic science process skills. The pre-service teachers were studied to see how they developed an understanding of the process skills and of co-teaching. The results showed how the pre-service teachers learned the process skills and how they learned about co-teaching. The co-teaching experience was particularly useful in that the pre-service teachers expressed the roles that co-teachers assume when they are in the classroom. This study shows that pre-service teachers should be made aware of co-teaching at the preparatory level and be able to practice co-teaching before being expected to know how to co-teach when they reach a classroom of their own.

Metal-organic and aerosol-assisted chemical vapor deposition. Development and application of dithiocarbamate and phosphinoborate ligand-based precursors for cuprous sulfide, molybdenum disulfide/titanium oxide, and metallic silver thin films

McCain, Matthew Neal Northwestern University 2007 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Chemical vapor deposition (CVD) is a well-developed technique for growing thin films of a wide variety of materials, which relies on the development of new and better performing metal-organic precursors. To this end, three studies have been conducted into the compatibility of sulfur and phosphine containing ligands with low- and high-valent transition metals to develop precursors for thin film growth. First, bis(di(2,2,2-trifluoroethyl)dithiocarbamato)copper(II) ( 1.1) has been synthesized, fully characterized, and implemented for the deposition of high quality cuprous sulfide thin films on amorphous glass substrates by metal-organic (MO) CVD. Thermogravimetric analysis (TGA) shows improved volatilization and mass transport of the precursor due to fluorination of the ligand framework. Films deposited in the presence of O2 at 350°C are phase-pure polycrystalline Cu1.96S with p-type conductivity of 68 S/cm and an optical band gap of 1.8 eV. Next, MoS2 thin films have been deposited onto 52100 steel substrates by aerosol-assisted (AA) CVD using the metal-organic precursor tetrakis(diethyldithiocarbamato)molybdenum(IV) (2.1). Film analysis indicates growth of an initial, highly crystalline FeS layer exhibiting preferred orientation parallel to the substrate, followed by growth of MoS2 nanoparticles. Friction coefficients for MoS2-coated steel specimens reach 0.10 when tested at 100°C in air. Codeposition by AACVD of tetrakis( tert-butylthiolato)titanium(IV) (2.2) with complex 2.1 yields nanoparticle films of variable TiO2 content as a result of solvent decomposition on the MoS2 surface and oxidation of TiS2. Finally, a series of light- and air-stable tris(phosphino)borato silver(I) complexes has been synthesized, structurally and spectroscopically characterized, and implemented in the growth of low resistivity metallic silver thin films by AACVD. One member of the series, [nBuB(CH 2PPh2)3]AgPEt3 (3.2), represents a significant improvement over previously available non-fluorinated Ag precursors, owing to ease of handling and efficient film deposition characteristics. TGA shows that the thermolytic properties of these complexes can be significantly modified by altering the ligand structure. Polycrystalline cubic-phase Ag thin films were grown on glass, MgO(100), and 52100 steel substrates. Ag films of thicknesses 3 mum, grown at rates of 14-18 nm/min, exhibit low levels of extraneous element contamination by x-ray photoelectron spectroscopy (XPS). Film growth proceeds primarily via an island growth (Volmer-Weber) mechanism.

The Preparedness of First-Year Football Student-Athletes in Online Classes at the University of Mississippi

McCain, Roy Clifford The University of Mississippi ProQuest Dissertatio 2020 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Colleges and universities in the United States currently face an n issue of student-athletes enrolling in online courses and not being prepared. Research has shown that students take these classes for a variety of reasons and perceive a variety of advantages and disadvantages to these types of classes and even more specifically, the subjects taken in the online format. Their level of preparedness, the reasons for this level, and the perceived assistance needed were also issues to be examined. This study aims to determine how prepared for online courses the first-year football student - athletes were during the 2018-2019 school year. In addition, it seeks to determine how these and other student-athletes can be better prepared for their first college online course. Based on a review of the literature on online education and theories of student success, online teaching and learning, and social class, face-to-face interviews were conducted with fourteen first-year football student-athletes at The University of Mississippi. Analysis of the responses demonstrated that the students had different perceptions of what could help future student-athletes attempting their first online class. On this basis, several recommendations on the building and departmental level were made to help student-athletes be more prepared for an online course in their first year.

A Study of Quality Requirement Conveyance for Assignments in Technology and Engineering Master’s Degree Programs

McCain, Heather J Indiana State University ProQuest Dissertations & 2020 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Quality requirements are not easy to define. In higher education, defining quality requirements and communicating those requirements to students may be accomplished through a variety of mechanisms. Students still may not know what it takes to get a good grade on an assignment and may have to wait for an instructor to clarify the assignment. This study was conducted because students and instructors may have different opinions as to which forms of feedforward and what technology are best to convey assignment requirements. The purpose of this study was to determine effective feedforward mechanisms as well as the technology used to convey quality requirements for assignments. A Delphi Panel was utilized to identify feedforward mechanisms as well as technology currently used. A survey was conducted to quantify waste in the assignment process via statistical testing. Minitab 19 with selected T-tests were used to determine if there is a difference between students and instructors as to what feedforward mechanisms or combinations of feedforward mechanisms are preferred to effectively convey quality requirements. The study involved Master-degree seeking students and instructors as well as university resources from teaching excellence programs from three universities. Combining the information from the Delphi Panel and the survey, a model was created that using the syllabus and instructions as mechanisms to convey quality requirements for assignments. Depending on the assignment a rubric, criteria sheet, or model/sample may be used to clarify requirements. Using the web-based learning management system allows students to access information outside of the classroom and at any time. The LMS can contain written as well as video or audio recordings of assignment information. The results of this study have led to improvements in a Project Management course at the University of Kansas.

A School-Based Cognitive-Behavioral Intervention for Students With Emotional or Behavioral Disorders

McCain, Skyler University of Florida ProQuest Dissertations & The 2024 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Students with emotional or behavioral disorders (EBD) often display externalizing behaviors (e.g., aggression and defiance) and experience internalizing symptoms (e.g., anxiety and depression). When left untreated, these difficulties can result in negative outcomes for students in school and beyond. Cognitive-behavioral interventions (CBIs) offer a promising approach to address the needs of students with EBD. Extensive evidence demonstrates the effectiveness of cognitive-behavioral treatment in clinical settings, but fewer studies have explored the effects of manualized CBIs provided to students at school.The purpose of this study was to evaluate the effects of the Zones of Regulation, a widely-used CBI, on the externalizing and internalizing behaviors of middle school students served for EBD. This single-subject investigation implemented a multiple baseline design across five participants served in a self-contained special education classroom. Participating students received the Zones of Regulation lessons one-on-one from the researcher across six weeks of school. Data was collected through direct observations of the classroom, student reports on the Behavior and Feelings Survey, and teacher reports on the Strengths and Difficulties Questionnaire.Although students demonstrated declines in their use of verbal aggression, visual analysis indicated that there was no functional relation between the Zones of Regulation intervention and the reduction of externalizing or internalizing behaviors for participating students. The descriptive statistics for mean rates of verbal aggression across phases suggest that there were reductions in student externalizing behaviors, but these changes were not robust enough to meet the rigorous criteria of single-subject design. More research is needed to determine whether the Zones of Regulation program can reduce internalizing and externalizing behaviors when administered as a Tier 3 intervention for students with EBD.

Conserving individual autonomy in exile: Hans Habe's struggle against totalitarianism (Austro-Hungary)

McMurray, David McCain Vanderbilt University 2001 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

My dissertation investigates the writings of Hans Habe (Janos Békessy 1911–1977), a prolific German-speaking novelist (26 major works) and journalist of Austro-Hungarian citizenship, who because of his Jewish ancestry was forced to flee National Socialism following the <italic>Anschluß </italic> of Austria in 1938. This chronological examination of Habe's career as a conservative, anti-Fascist writer analyzes his developing concept of the “autonomous individual” with regard to the rise of National Socialism, its legacy in postwar Europe and the general dehumanizing effects of totalitarian regimes. An in-depth analysis of Habe's early novels demonstrates both his astute literary engagement contra National Socialism and the role he foresaw for the German exile-writer. Habe's criticism of the early German emigration (<underline>Drei über die Grenze</underline>,1937) and his portrayal of the individual's plight with regard to totalitarianism (<underline> Zu Spät</underline>, 1939) substantiate his thesis that the maintenance of “individual autonomy” in exile could best effectuate a displaced emigrant's “democratic” encounter with postwar Germany. Habe's identification with his new “stateless” status and his cosmopolitan adherence to a German “cultural identity” (rather than a “national identity”) are further demonstrated in his work for the US Army's Psychological Warfare Division (1942–45), the 12<super>th</super> Army Group Press (1945), and his editorship of the American-sponsored <underline>Die Neue Zeitung </underline> (1945–46). Habe's consistent attempts to rejoin the cultural and literary traditions of pre-war Germany and his appeals for individual responsibility and democratic renewal manifested in the interim postwar press are an actualization of his persistent belief in the humanistic ideals of “the other Germany.” An analysis of Habe's polemical engagement with the postwar German literary intelligentsia and the government of the Federal Republic authenticate the continued relevance of his contemporary social criticism for historians and literary critics alike. Habe's identification with “German culture,” the “permanence of exile,” and his vigilance regarding the threats to individual liberty posed by monopolizing collectives from both the political right and the political left, all contributed to his understanding that the “autonomous individual” was requisite in the collective pursuit of democratic freedom.