Distance education as delivery mode is currently attracting more and more learners globally who want to improve their skills and qualifications. This is necessitated by especially the limited components of existing contact universities, financial expenditure and working learners. The presenting of open distance learning by existing contact universities in South Africa is relatively unknown. Consequently the aim of this study is also to investigate a model for Open Distance Learning used at the NWU, an existing contact university. In order to achieve this aim, several other aims were set as well. The most important findings of these aims are subsequently summarized. Aim one was to determine how distance education, open distance learning and e-learning have been conceptualized in the literature. It emerges clearly from the literature that various barriers and challenges accompany the implementation and delivery of distance and open distance learning program. These barriers particularly concern matters such as academic, cultural and technical aspects like the student’s experience, the position of the lecturer regarding the program, the design of the program, the fact that development in technology is constantly kept in mind and kept up with, as well as problems with financial aspects. The second aim intended to compare open distance learning in developed and developing countries as far as contact classes and e-learning are concerned, in order to establish the best practices for a suitable management model. The open distance learning models of twelve universities were examined separately and compared to one another. From these comparisons the following components of open distance learning were indentified which would be applicable to both developing and developed countries: (i) the use of traditional paper-based study material; (ii) the use of various forms of technology; (iii) the use of e-learning, and (iv) voluntary supporting contact classes. From the literature it has been shown that, despite limited infrastructure, poverty, illiteracy and geographical isolation, e-learning and m-learning are increasingly implemented as delivery modes in open distance learning programmes in developing as well as developed countries. Aim three was to establish, from within the literature, the nature of management models with specific reference to the innovations within managing business models in the context of open distance learning. Firstly variables which play a role in new business models were considered. Secondly the levels according to which the innovation of new models should take place were investigated, and also how these could possibly be implemented within the NWU, as well as the principles applicable to the innovation and implementing of a new model from an existing mother company. Factors which could play a part in the plans to present distance learning programs were also considered, whether these would imply a new distance education unit or the continued presentation of such programs. The most important aspects to consider for such a management model are addressed in aim seven. Aim four investigated the effect of attendance or non-attendance of contact classes on the academic achievement of open distance learning students within selected Advanced \certificate in Education (ACE) programs. This aim referred to an empirical investigation which comprised five phases. A consecutively progressing research design was used, consisting of both quantitative and qualitative methods, known as the multi-mode design. Phases one to three address aim four. Spearman’s rank order correlations, one-way ANOVAs (t-tests) and two-way tables (Cramer’s effect sizes) were calculated in order to identify significant correlation (effect sizes) between variables. It was found that students who attended contact classes did not achieve significantly better during examinations than students who did not attend. The average module mark in the examination of students who did not attend contact classes was 49.5%. The average mark of students who attended three or more contact classes was 52.6%. Considering the examination results, the passing rate of students who attended contact classes was 89% as opposed to 82% for those who did not attend any contact classes. Upon comparing data of students attending vacation school and those who did not, it emerged that students who attended vacation school achieved an average module mark (for all modules) of 42.4% as opposed to 52.7% of those who did not attend any vacation school. Aim five considered the open distance learning student’s opinions on and experience of attending contact classes and not attending, within selected ACE programs. Questionnaires were distributed to a number of students who attended contact classes, and to some who did not attend. The following findings emerged: reasons why students do not attend contact classes are (i) distance from tuition centre; (ii) personal reasons such as family responsibilities or funerals; (iii) because classes are not presented by full-time NWU lecturers; (iv) medium of instruction, limited time and class sizes also seemed to pose problems. Aim six investigated the readiness of the open distance learning student for e-learning within selected ACE programs. Focus group interviews regarding this aim were conducted with three groups of students. The following was found: (i) the vast majority of students (62.1%) do not have computers at home; (ii) 80.4% indicated that that they could not access the Internet, and that (iii) cell phone communication seemed to be the solution, since 93.1% of students own cell phones. Aim seven investigated the opinions of management experts at the NWU concerning the components and practice of an ODL model at the NWU. In order to comply with this aim, an intensive literature study was done on open distance learning models internationally. In the second place an empirical investigation was conducted regarding attendance of contact classes and e-learning as teaching method for the teaching and learning component of an open distance learning model. Thirdly focus group interviews were conducted with senior management of the NWU regarding challenges, risks and components of an open distance learning model. According to the data obtained from these interviews, various matrix analyses were done, which could serve as basis for a management model in open distance learning. The matrix analyses identified the following eleven components as important for a management and practice model for open distance learning: (i) Teaching and learning pertaining to development and quality of study material, effective assessment, the required program designers, training of lecturers and facilitators for presenting open distance learning programs, and efficient quality evaluation. (ii) ITC for open distance learning refers to technological support for processes such as assessment, interactive presentation of lessons, using Internet, cell phone technology and the use of the web page. (iii) Support practice for management which involves matters such as the policy of administrative processes regarding registration, cooperation with consortiums, assessment of assignments and examinations, and dealing with administrative processes different from on-campus. (iv) Finances which refer to compiling annual budgets, remuneration of facilitators, determining the profitability of programs presented, as well as financing technological development. (v) Tuition centres: coordination between the university and tuition centres is crucial as far as contact classes, interactive presentations, group discussions as well as examinations are concerned. (vi) Short courses and projects, especially as far as continuing professional development is concerned, as well as the development of a preparatory college for prospective students and cooperation with private institutions. (vii) Quality processes which include compulsory evaluation of program content and of the effect of programs as evaluated by the private sector, identifying new programs and cooperation with other faculties. (viii) Marketing which can be done by the university itself or by a consortium of collaborators. (ix) A structure for open distance learning with its own, unique and particular structure according to need. Factors which may be significant are the number of students studying through open distance learning, the nature of the programs presented and cooperation between consortiums. (x) Hierarchical structure which in the first place requires effective management of an open distance unit, and secondly also that such unit functions in cooperation with and within existing structures. Especially executive authority and lines for reporting should be outlined clearly. (xi) Research must be done in collaboration with other faculties in order to acquire a particular distance education entity. Research regarding the management of, e.g. the effect of programs, contact class attendance, readiness for e-learning and technology at tuition centres, can also be conducted. The exigency for development of an o pen distance learning unit within the NWU, together with a management model for effective management and practice of distance programs, was the main theme of this study. This study has succeeded in suggesting a management model which could be utilized profitably in endeavoring to attain the strategic aim of presenting programs by means of distance education. It also addresses the national need in South Africa of access to tertiary education for more learners. / PhD (Education Management), North-West University, Potchefstroom Campus, 2012

Made available in DSpace on 2014-12-17T14:54:50Z (GMT). No. of bitstreams: 1 CaioDC.pdf: 2782026 bytes, checksum: ffc0e89b5e796daecc6152d3075b6918 (MD5) Previous issue date: 2008-01-24 / The so-called Dual Mode Adaptive Robust Control (DMARC) is proposed. The DMARC is a control strategy which interpolates the Model Reference Adaptive Control (MRAC) and the Variable Structure Model Reference Adaptive Control (VS-MRAC). The main idea is to incorporate the transient performance advantages of the VS-MRAC controller with the smoothness control signal in steady-state of the MRAC controller. Two basic algorithms are developed for the DMARC controller. In the first algorithm the controller's adjustment is made, in real time, through the variation of a parameter in the adaptation law. In the second algorithm the control law is generated, using fuzzy logic with Takagi-Sugeno s model, to obtain a combination of the MRAC and VS-MRAC control laws. In both cases, the combined control structure is shown to be robust to the parametric uncertainties and external disturbances, with a fast transient performance, practically without oscillations, and a smoothness steady-state control signal / Neste trabalho ? apresentada uma proposta de um controlador, denominado Controlador em Modo Dual Adaptativo Robusto (DMARC), que estabelece uma liga??o entre um controlador adaptativo por modelo de refer?ncia (MRAC) e um controlador adaptativo por modelo de refer?ncia e estrutura vari?vel (VS-MRAC). A id?ia b?sica ? incorporar as vantagens de desempenho transit?rio do controlador VS-MRAC com as propriedades de regime permanente do controlador MRAC convencional. S?o desenvolvidos dois algoritmos b?sicos para o controlador DMARC. No primeiro o ajuste do controlador ? feito, em tempo real, atrav?s da varia??o de um par?metro na lei de adapta??o. No segundo algoritmo a lei de controle ? gerada, utilizando o modelo Takagi-Sugeno da l?gica nebulosa, para obter uma composi??o ponderada das leis de controle do MRAC e do VS-MRAC. Em ambos os casos, o esquema combinado de controle ? mostrado ser robusto ?s incertezas param?tricas e perturba??es externas, al?m de apresentar um desempenho r?pido e pouco oscilat?rio durante o transit?rio e um sinal de controle suave em regime permanente

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[ES] Históricamente, el sector del transporte de servicio mediano y pesado ha sido desafiado por las regulaciones de emisiones que se han impuesto a lo largo de los años, lo que requirió intensificar el esfuerzo de investigación con el objetivo de avanzar en el desarrollo tecnológico para ofrecer una opción que cumpla con las normas a un precio similar para el propietario. No obstante, la reciente introducción de la normativa EUVI ha requerido la adición de un complejo sistema de postratamiento, agregando nuevos costes fijos al producto, así como costes operativos con el consumo de urea. Este avance fue necesario debido a la limitación de la combustión diésel convencional que no puede desacoplar las altas emisiones de NOx y la eficiencia. Esta limitación tecnológica ha impulsado la investigación sobre diferentes conceptos de combustión que podrían mantener niveles de eficiencia similares a los de la combustión diésel controlando la formación de emisiones durante el proceso de combustión. Entre las diferentes soluciones que han ido apareciendo a lo largo de los años, se demostró que la Ignición por Compresión Controlada por Reactividad (RCCI por sus siglas en inglés) tiene una ventaja competitiva debido a su mejor controlabilidad, alta eficiencia y bajas emisiones de hollín y NOx. A pesar de sus beneficios, la extensión de RCCI a la operación de mapa completo ha indicado limitaciones importantes como gradientes de presión excesivos a alta carga, o alta inestabilidad de combustión y productos no quemados a baja carga del motor. Recientemente, se introdujo el concepto de combustión Dual-Mode Dual-Fuel (DMDF) como un intento de resolver los inconvenientes de la combustión RCCI manteniendo sus ventajas. Los resultados preliminares obtenidos en un motor mono cilíndrico (SCE por sus siglas en inglés) han demostrado que el DMDF puede alcanzar niveles de eficiencia similares a los de la combustión diésel convencional al mismo tiempo que favorece niveles ultra bajos de hollín y NOx. Si bien, los requisitos de la condición límite son difíciles de encajar en el rango operativo de sistema de gestión de aire, así como inconvenientes como el exceso de HC y CO que aún persiste en la zona de baja y media carga, lo que puede ser un desafío para el sistema de postratamiento. Además, las futuras regulaciones a corto plazo exigirán una reducción del 15 % de las emisiones de CO2 en 2025, reto que la literatura sugiere que no se logrará fácilmente solo mediante la optimización del proceso de combustión. En este sentido, esta tesis tiene como objetivo general la implementación del concepto de combustión DMDF en un motor multicilindro (MCE por sus siglas en inglés) bajo las restricciones de las aplicaciones reales para realizar una combustión limpia y eficiente en el mapa completo a la vez que brinda alternativas para reducir la concentración de HC y CO y lograr un ahorro de CO2. Este objetivo se logra mediante un primer extenso procedimiento de calibración experimental que tiene como objetivo trasladar las pautas de la combustión DMDF del SCE al MCE respetando los límites operativos del hardware original, evaluando su impacto en los resultados de combustión, rendimiento y emisiones en condiciones estacionarias y condiciones de ciclo de conducción. A continuación, se realizan estudios específicos para abordar el problema relacionado con la concentración excesiva de productos no quemados mediante investigaciones experimentales y simulaciones numéricas para comprender las consecuencias del uso de combustibles con diferente reactividad en la eficiencia de conversión del catalizador de oxidación original y su capacidad para lograr emisiones en el escape menores que el límite EUVI. Finalmente, se busca la reducción de CO2 a través de la modificación del combustible, investigando tanto la mejora del proceso de combustión como el equilibrio entre el ciclo de vida del combustible. / [CA] Històricament, el sector del transport de servei mitjà i pesat ha sigut desafiat per les regulacions d'emissions que s'han imposat al llarg dels anys, la qual cosa va requerir intensificar l'esforç d'investigació amb l'objectiu d'avançar en el desenvolupament tecnològic per a oferir una opció que complisca amb les normes a un preu similar per al propietari. No obstant això, la recent introducció de la normativa EUVI ha requerit l'addició d'un complex sistema de postractament, agregant nous costos fixos al producte, així com costos operatius amb el consum d'urea. Aquest avanç va ser necessari a causa de la limitació de la combustió dièsel convencional que no pot desacoblar les altes emissions de NOx i l'eficiència. Aquesta limitació tecnològica ha impulsat la investigació sobre diferents conceptes de combustió que podrien mantindre nivells d'eficiència similars als de la combustió dièsel controlant la formació d'emissions durant el procés de combustió. Entre les diferents solucions que han anat apareixent al llarg dels anys, es va demostrar que la Ignició per Compressió Controlada per Reactivitat (RCCI per les seues sigles en anglés) té un avantatge competitiu a causa de la seua millor controlabilitat, alta eficiència i baixes emissions de sutge i NOx. Malgrat els seus beneficis, l'extensió del RCCI a l'operació de mapa complet ha indicat limitacions importants com a gradients de pressió excessius a alta càrrega, o alta inestabilitat de combustió i productes no cremats a baixa càrrega del motor. Recentment, es va introduir el concepte de combustió Dual-Mode Dual-Fuel (DMDF) com un intent de resoldre els inconvenients de la combustió RCCI mantenint els seus avantatges. Els resultats preliminars obtinguts en un motor mono-cilíndric (SCE per les seues sigles en anglés) han demostrat que el DMDF pot aconseguir nivells d'eficiència similars als de la combustió dièsel convencional al mateix temps que afavoreix nivells ultra baixos de sutge i NOx. Si bé, els requisits de la condició límit són difícils d'encaixar en el rang operatiu de sistema de gestió d'aire, així com inconvenients com l'excés de HC i CO que encara persisteix en la zona de baixa i mitja càrrega, la qual cosa pot ser un desafiament per al sistema de postractament. A més, les futures regulacions a curt termini exigiran una reducció del 15% de les emissions de CO¿ en 2025, repte que la literatura suggereix que no s'aconseguirà fàcilment només mitjançant l'optimització del procés de combustió. En aquest sentit, aquesta tesi té com a objectiu general la implementació del concepte de combustió DMDF en un motor multi-cilindre (MCE per les seues sigles en anglés) sota les restriccions de les aplicacions reals per a realitzar una combustió neta i eficient en el mapa complet alhora que brinda alternatives per a reduir la concentració de HC i CO i aconseguir un estalvi de CO¿. Aquest objectiu s'aconsegueix mitjançant un primer extens procediment de calibratge experimental que té com a objectiu traslladar les pautes de la combustió DMDF del SCE al MCE respectant els límits operatius del motor original, avaluant el seu impacte en els resultats de combustió, rendiment i emissions en condicions estacionàries i condicions de cicle de conducció. A continuació, es realitzen estudis específics per a abordar el problema relacionat amb la concentració excessiva de productes no cremats mitjançant investigacions experimentals i simulacions numèriques per a comprendre les conseqüències de l'ús de combustibles amb diferent reactivitat en l'eficiència de conversió del catalitzador d'oxidació original i la seua capacitat per a aconseguir emissions al tub d'escapament menors que el límit EUVI. Finalment, es busca la reducció de CO2 a través de la modificació del combustible, investigant tant la millora del procés de combustió com l'equilibri entre el cicle de vida del combustible. / [EN] The medium and heavy-duty transport sector was historically challenged by the emissions regulations that were imposed along the years, requiring to step up the research effort aiming at advancing the product development to deliver a normative compliant option at similar price to the owner. Nonetheless, the recent introduction of EUVI normative have required the addition of a complex aftertreatment system, adding new fixed costs to the product as well as operational costs with the urea consumption. This breakthrough was required due to the limitation of the conventional diesel combustion which cannot decouple high NOx emissions and efficiency. This technological limitation has boosted the investigation on different combustion concepts that could maintain similar efficiency levels than the diesel combustion while controlling the emission formation during the combustion process. Among the different solutions that have appeared along the years, Reactivity Controlled Compression Ignition (RCCI) was demonstrated to have a competitive edge due to its better controllability, high efficiency and low soot and NOx emissions. Despite the benefits, the extension of RCCI to full map operation has presented significant limitations, as excessive pressure gradients at high load and high combustion instability and unburned products at low engine load. Recently, Dual-Mode Dual-Fuel (DMDF) combustion concept was introduced as an attempt of solving the drawbacks of the RCCI combustion while maintaining its advantages. The preliminary results obtained in single cylinder engine (SCE) have evidenced that DMDF can achieves similar efficiency levels than those from conventional diesel combustion while promoting ultra-low levels of soot and NOx. Albeit, the boundary condition requirements are hard to fit in the operating range of commercial air management system as well as drawbacks like excessive HC and CO that still persists from low to medium load, which can be a challenge for the aftertreatment system. Moreover, short-term future regulations will demand a 15 % reduction of CO2 emissions in 2025 which was proven in the literature to not be easily achieved only by combustion process optimization. In this sense, this thesis has as general objective the implementation of the DMDF combustion concept in a multi-cylinder engine (MCE) under the restrictions of real applications to realize clean and efficient combustion in the complete map while providing alternatives to reduce the HC and CO concentration and accomplish CO2 savings. This objective is accomplished by means of a first extensive experimental calibration procedure aiming to translate the guidelines of the DMDF combustion from the SCE to the MCE while respecting the operating limits of the stock hardware, assessing its impacts on combustion, performance, and emission results under steady and driving cycle conditions. Next, dedicated studies are performed to address the issue related with the excessive concentration of unburned products by means of experimental investigations and numerical simulations, to understand the consequences of using fuels with different reactivity in the stock oxidation catalyst conversion efficiency and its ability in achieving EUVI tailpipe emissions. Finally, CO2 reduction is explored through fuel modification, investigating both combustion process improvement and well-to-wheel balance as paths to realize CO2 abatement. / This doctoral thesis has been partially supported by the Spanish Ministry of Science Innovation and Universities under the grant:"Ayudas para contratos predoctorales para la formación de doctores" (PRE2018-085043) / Lago Sari, R. (2021). Dual Mode Dual Fuel Combustion: Implementation on a Real Medium Duty Engine Platform [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/165366

Distance education (DE) is now recognised as an education system independent from conventional face-to-face education. It has self-governing theories and pedagogies. It attracts students with unique characteristics different from those of on-campus students. The present distance learning student differs from the past ones by characteristics, needs and contexts. Not all students registering for distance learning conform to the characteristics of distance students described in theory. It is now acknowledged that DE systems demand special skills including time management, self-regulation and independent learning skills. Yet, few of these students enter into distance learning with prior experiences on its demands. The new student is compelled to learn to deal with challenges that come with DE i.e. the impact of ‘distance’, isolation and time management. ‘The net generation’ and ‘digital natives’ are now in college but with skills not automatically transferable to learning technologies. Information and communication technologies (ICT) providers are mostly focused on the ‘use’ rather than the ‘user’. Universities are continuously adopting new technologies leaving the student bewildered as to the focus; learning or technology training. The internet has ‘everything’; open course ware (OCW), open education resources (OERS), wikis and all web information. Students cannot simply find things for themselves. Furthermore distance learning has no policy on how to engage with the internet and students are left to decide what, which and how much is required for any level of study. Most universities in Africa moving from single to dual mode have not integrated distance learning pedagogy which requires restructuring in the organisation, policy and course development. DE, though spanning over two centuries has been mutually dependent on technology. The present technology demands a paradigm shift from that of correspondence days. These issues have created the need for support strategies that can literally accompany the DE student throughout his/her academic journey. Universities have established DE units, campuses and schools for a variety of reasons. It is required that such universities provide learner support systems for their students. The purpose of this study was to assess the learner support services available for distance learning undergraduate students in two universities in Kenya i.e. Northern University (NU) and Western University (WU). A Learner support system can comprise of numerous components. In this study, nine (9) components/indices were tested as the indices for providing support services. These are:- registration procedures, orientation programme and skills training, technology and learning materials, counselling and mentorship, interactions and communication, feedback, regional centres and library, students association and representation and course progression and satisfaction. This study employed an evaluation research design utilising both quantitative and qualitative methods. Online questionnaires were used for quantitative data collection. For qualitative data collection two (2) instruments were used; an interview schedule for key programme implementers and a documentary analysis tool for documents and websites. The findings indicated that the main indices that distinguished the two universities were registration process, technology and learning materials, counselling/mentorship and regional centres where the t-test showed significant differences. The p values were 0.008, 0.012, 0.036 and 0.015 respectively at 0.05 significance level. In all of them, Northern University (NU) had a relatively high mean score than Western University (WU) except for the index on counselling and mentorship. / Educational Foundations / D. Ed. (Socio-Education)

Distance education (DE) is now recognised as an education system independent from conventional face-to-face education. It has self-governing theories and pedagogies. It attracts students with unique characteristics different from those of on-campus students. The present distance learning student differs from the past ones by characteristics, needs and contexts. Not all students registering for distance learning conform to the characteristics of distance students described in theory. It is now acknowledged that DE systems demand special skills including time management, self-regulation and independent learning skills. Yet, few of these students enter into distance learning with prior experiences on its demands. The new student is compelled to learn to deal with challenges that come with DE i.e. the impact of ‘distance’, isolation and time management. ‘The net generation’ and ‘digital natives’ are now in college but with skills not automatically transferable to learning technologies. Information and communication technologies (ICT) providers are mostly focused on the ‘use’ rather than the ‘user’. Universities are continuously adopting new technologies leaving the student bewildered as to the focus; learning or technology training. The internet has ‘everything’; open course ware (OCW), open education resources (OERS), wikis and all web information. Students cannot simply find things for themselves. Furthermore distance learning has no policy on how to engage with the internet and students are left to decide what, which and how much is required for any level of study. Most universities in Africa moving from single to dual mode have not integrated distance learning pedagogy which requires restructuring in the organisation, policy and course development. DE, though spanning over two centuries has been mutually dependent on technology. The present technology demands a paradigm shift from that of correspondence days. These issues have created the need for support strategies that can literally accompany the DE student throughout his/her academic journey. Universities have established DE units, campuses and schools for a variety of reasons. It is required that such universities provide learner support systems for their students. The purpose of this study was to assess the learner support services available for distance learning undergraduate students in two universities in Kenya i.e. Northern University (NU) and Western University (WU). A Learner support system can comprise of numerous components. In this study, nine (9) components/indices were tested as the indices for providing support services. These are:- registration procedures, orientation programme and skills training, technology and learning materials, counselling and mentorship, interactions and communication, feedback, regional centres and library, students association and representation and course progression and satisfaction. This study employed an evaluation research design utilising both quantitative and qualitative methods. Online questionnaires were used for quantitative data collection. For qualitative data collection two (2) instruments were used; an interview schedule for key programme implementers and a documentary analysis tool for documents and websites. The findings indicated that the main indices that distinguished the two universities were registration process, technology and learning materials, counselling/mentorship and regional centres where the t-test showed significant differences. The p values were 0.008, 0.012, 0.036 and 0.015 respectively at 0.05 significance level. In all of them, Northern University (NU) had a relatively high mean score than Western University (WU) except for the index on counselling and mentorship. / Educational Foundations / D. Ed. (Socio-Education)

This study is a collective case study grounded in the literature regarding leadership styles and leadership theories. It includes among others, an analysis of data from interviews of college Principals and middle Managers to identify the leadership styles at the three colleges of education. The purpose of the study was to analyse the leadership styles of college Principals and middle Managers operating in dual-mode environments. The colleges that were being studied are the Copperbelt College of Education; Mufulira College of Education and Malcom Moffat College of Education. There were sixteen (16) participants in this study drawn from three colleges. The researcher collected data using semi-structured individual and focused group interviews. In addition, policy documents such as ‗Open and Distance Learning Policy (draft) and National Policy on Education were analysed. The researcher employed qualitative methods in the collection and analysis of data. Triangulation was used in order to verify the information given during this study. The evidence from the literature review indicates that there is no single leadership style that may provide answers to all situations in institutions of higher education; rather, a blend of the leadership styles would be beneficial to college Principals. The research further revealed that, managing dual-mode colleges of education entails that Principals require tailor-made programmes in management and leadership of dual-mode institutions for them to improve quality of their products and enhance tenets of transparency, democracy and good governance in colleges of education in Zambia. They also must be excellent communicators and ensure understanding by students, employees, peers, and the many stakeholders involved in dual-mode colleges of education. The study was important as it hoped to shed some light on how to improve quality of leadership in dual-mode colleges of education in Zambia. The study will contribute scientific knowledge to all categories of Higher Education (HE) institutions especially colleges of education, be they face-to-face or distance mode, that are contemplating a move into dual-mode delivery. Finally, Information garnered from this study is expected to allow Principals and other middle Managers and administrators to evaluate their leadership styles in comparison to the effective styles revealed by this study. / Educational Leadership and Management / D. Ed. (Education Management)

<p>Prior to the mid-20th century, the idea of electric propulsion had been all but a foreign one that manifested itself in the topic of science fiction. It was around this time when companies and agencies like NASA began to take interest in the topic of space propulsion, as most famously seen in the landing of the Apollo 11 mission on the moon. It was not until the early-1960s where the idea of a pulsed plasma thruster was first realized, with its first test being in 1964 aboard the Russian Zond-2 satellite which contained 6 ablative Polytetrafluoroethylene (PTFE, or “Teflon”) pulsed plasma thrusters.</p> <p>In this paper, a new low-voltage, liquid-fed pulsed plasma thruster was developed, tested, and characterized. This project took influence from the previous low-voltage, liquid-fed pulsed plasma thruster in Purdue’s EPPL and desired to transition it from a current gas-fed system to its intended liquid-fed system. The two main objectives for this project included conducting direct studies of the cathode’s erosion rate using a simple weighing method after simulating a lifetime of discharging the thruster, and completing the initial design of the liquid-fed pulsed plasma thruster using AF-M315E as its propellant while gathering data on its required breakdown voltage, exhaust velocity, and specific impulse.</p> <p>Both objectives were successfully completed, with the following parameters being measured or calculated. The required breakdown voltage was seen to be less than 26kV to keep the ignition spark inside the chamber. For the subsequent results measured however, the breakdown voltage was kept between 10-16kV for all successive tests. The peak current measured for all discharges was an average of 11kA, far exceeding similar geometries such as MPD thrusters. The operational voltage was less than 200V, although an operational voltage closer to 100V is expected after further optimization of the system is completed. The erosion rate of the tungsten cathode at this operational setting was found to be 15.4046 +/- 0.592 microgram/Coulomb which is much less than the cathode spot erosion rate reported for tungsten in literature of about 60 microgram/Coulomb and is beneficial for extending system lifetime. The exhaust velocity was calculated to be 30.6 +/- 4.8km/s which is typical of state-of-the-art PPT electric propulsion devices. The specific impulse was also extrapolated from the ion’s exhaust velocity, calculating to be 3,119 +/- 489 seconds. Future work would require optimization of the propellant injection mechanism to minimize propellant loss.</p>

The promising role resistive random-access memory (RRAM) plays in the imminent reality of wearable electronics calls for a new, updated physical model of their operating mechanism. Their high applicability as the next-generation flexible non-volatile memory (NVM) devices has promoted the recent emergence of a novel ultra-thin (&lt; 5nm) organic/inorganic hybrid dielectric RRAM. A deep understanding of their resistive switching (RS) behavior is required to unlock their suitability in future electronics applications. However, the extremely reduced thicknesses bring about new challenges in terms of material characterization sample processing, while the RS observations through electrical characterization techniques lack uniformity in the key switching parameters, thus hindering the identification of any clear trends.  This work studies the RS mechanism in ultra-thin Al/Hf-hybrid/Ni RRAM devices through uniformity-improved electrical observations. First, the focus is to implement a ramped-pulse train method during the reset process to reduce the dispersion of the voltage and resistance fluctuations at different starting voltage amplitudes and pulse widths. After finding the optimal electrical programming conditions for reduced parameter dispersions, a temperature test was performed to study the contributions of the metal ions and oxygen vacancies (V2+) in the switching layer. Finally, a physical model describing the operating mechanism in flexible RRAM is proposed after the close observation and study of the processed devices. The model is based on the coexistence of a hetero-metallic portion composed of Al and Hf3Al2, and a V2+ portion connected to form the hybrid conducting filament (CF) and turning the device on. The CF forming processes emphasize the strong presence of these vacancies partaking in RS, as the temperature dependence results suggest the majority of their concentration to be generated during this step. Also, the different electrical potential, temperature, and concentration gradients influencing the V2+ migration during RS may explain some of the failure mechanisms in the rupture and the re-forming of the filament. Additionally, the possible presence of a thin Al-oxide layer in the Al/Hf-hybrid interface may give a reason for leaky on-states. A detailed physical model of the RS mechanism in next-generation flexible RRAMs is key to learn to unlock a range of emerging technologies fitted to today’s needs. / Den senaste introduktionen av ultratunn (&lt;5 nm) organisk-oorganisk hybrid dielektrisk RRAM som nästa generations icke-flyktiga minnesenheter kräver en djup förståelse för hybridskiktresistiv växling (RS). Den extremt reducerade tjockleken hindrar emellertid deras bearbetbarhet för materialkarakteriseringstekniker. Dessutom hindrar den dåliga enhetligheten i viktiga omkopplingsparametrar fortfarande i RRAM att alla trender kan definieras tydligt genom elektrisk karakterisering. Detta arbete använder elektrisk manipulation genom en RPS-metod (ramped-pulse series) för att förbättra spännings- och motståndsfluktuationerna i återställningsprocessen för ultratunna Al/Hf-hybrid/Ni-enheter vid olika spänningsamplitud, pulsbredd och temperaturförhållanden. Från de erhållna RPS-optimerade resultaten föreslås en ny och detaljerad fysisk modell som beskriver driftsmekanismen. Samexistensen i den ledande filamenten (CF) av en hybridmetalldel, sammansatt av Al och Hf3Al2, och en syrevakansdel bekräftas. Vår modell betonar vakansbidraget i RS, där majoriteten genereras under CF-formningsprocessen och deltar i olika grad i filamentbrottet för RPS och ingen RPS-bearbetade enheter via Joule-uppvärmning, drift och Fick-krafter. Dessutom förklaras kopplingsfelhändelser baserat på närvaron av ett Al2O3-lager i Al/Hf-hybridgränssnittet.

[ES] La presente tesis doctoral tiene como principal objetivo el estudio, diseño, desarrollo y fabricación de nuevos dispositivos pasivos de microondas, tales como filtros y multiplexores con respuestas avanzadas para aplicaciones de alto valor añadido (i.e. comerciales, militares, espacio); orientados a distintos servicios, actuales y futuros, en sistemas inalámbricos de comunicación. Además, esta investigación se centrará en el desarrollo de filtros encapsulados de montaje superficial y con un elevado grado de miniaturización. Para ello, se propone investigar distintas técnicas que consigan respuestas muy selectivas o con unas características exigentes en rechazo (mediante la flexible introducción de ceros de transmisión), así como una excelente planaridad en banda (aplicando técnicas tales como la mejora del Q o el diseño de filtros con pérdidas, lossy filters), obteniendo de este modo respuestas mejoradas, con respecto a soluciones conocidas, en los componentes de microondas desarrollados. De forma general, la metodología seguida se iniciará con una búsqueda y conocimiento del estado del arte sobre cada uno de los temas que se acometerán en esta tesis. Tras ello, se establecerá un procedimiento de síntesis que permitirá acometer de forma teórica los objetivos y especificaciones a conseguir en cada caso. Con ello, se establecerán las bases para iniciar el proceso de diseño, incluyendo co-simulación circuital/electromagnética y optimización que permitirán, en última instancia, implementar la solución planteada en cada caso de aplicación concreto. Finalmente, la demostración y validez de todas las investigaciones realizadas se llevará a cabo mediante la fabricación y caracterización experimental de distintos prototipos. / [CA] La present tesi doctoral té com a principal objectiu l'estudi, disseny, desenvolupament I fabricació de nous dispositius passius de microones, com ara filtres i multiplexors amb respostes avançades per a aplicacions d'alt valor afegit, (comercials, militars, espai); orientats a oferir diferents serveis, actuals i futurs, en els diferents sistemes sense fils de comunicació. A més, aquesta investigació es centrarà en el desenvolupament de filtres encapsulats de muntatge superficial i amb un elevat grau de miniaturització. Per a això, es proposa investigar diferents tècniques que aconsegueixin respostes molt selectives o amb unes característiques exigents en rebuig (mitjançant la flexible introducció de zeros de transmissió), així com una excel·lent planaritat en banda (aplicant tècniques com ara la millora de l'Q o el disseny de filtres amb perdues, lossy filters), obtenint d'aquesta manera respostes millorades, respecte solucions conegudes, en els components de micrones desenvolupats. De forma general, la metodologia seguida s'iniciarà amb una recerca i coneixement de l'estat de l'art sobre cadascun dels temes que s'escometran en aquesta tesi. Després d'això, s'establirà un procediment de síntesi que permetrà escometre de forma teòrica els objectiusi especificacions a aconseguir en cada cas. Amb això, s'establiran les bases per iniciar el procés de disseny, amb co-simulació circuital / electromagnètica i optimització que permetran, en última instància, implementar la solució plantejada en cada cas d'aplicació concret. Finalment, la demostració i validesa de totes les investigacions realitzades es durà a terme mitjançant la fabricació i caracterització experimental de diferents prototips. / [EN] The main objective of this doctoral thesis is the study, design, development and manufacture of new passive microwave components, such as filters and multiplexers with advanced responses for commercials, military and space applications; oriented to other different services, in current and future wireless communication systems. In addition, this research will focus on the development of surface-mounted encapsulated filters with a high degree of miniaturization. With this purpose, it is proposed to investigate different techniques that achieve highly selective responses or with demanding characteristics in rejection (through the flexible introduction of transmission zeros), as well as an excellent in-band planarity (applying techniques such as the Q enhancement or lossy filters), thus obtaining improved responses, with respect to known solutions, in the developed microwave components. In general, the followed methodology will begin with a search and knowledge of the state of the art on each of the topics addressed in this thesis. After that, a synthesis procedure will be established, which will allow the achievement of the objectives and specifications in a theoretical way, for each case. With this, the bases will be established to start the design process, with circuital and electromagnetic co-simulations and optimizations that will allow, ultimately, to implement the proposed solution, in every application case, specifically. Finally, the demonstration and validity of all the investigations will be carried out through the manufacture and experimental characterization of different prototypes. / Marín Martínez, S. (2022). Microwave Filters in Planar and Hybrid Technologies with Advanced Responses [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/188943