861 resultados para Potential theory (Mathematics).
Resumo:
The large intrinsic bandgap of NiO hinders its potential application as a photocatalyst under visible-light irradiation. In this study, we have performed first-principles screened exchange hybrid density functional theory with the HSE06 functional calculations of N- and C-doped NiO to investigate the effect of doping on the electronic structure of NiO. C-doping at an oxygen site induces gap states due to the dopant, the positions of which suggest that the top of the valence band is made up primarily of C 2p-derived states with some Ni 3d contributions, and the lowest-energy empty state is in the middle of the gap. This leads to an effective bandgap of 1.7 eV, which is of potential interest for photocatalytic applications. N-doping induces comparatively little dopant-Ni 3d interactions, but results in similar positions of dopant-induced states, i.e., the top of the valence band is made up of dopant 2p states and the lowest unoccupied state is the empty gap state derived from the dopant, leading to bandgap narrowing. With the hybrid density functional theory (DFT) results available, we discuss issues with the DFT corrected for on-site Coulomb description of these systems.
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Dengue is an important vector-borne virus that infects on the order of 400 million individuals per year. Infection with one of the virus's four serotypes (denoted DENV-1 to 4) may be silent, result in symptomatic dengue 'breakbone' fever, or develop into the more severe dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Extensive research has therefore focused on identifying factors that influence dengue infection outcomes. It has been well-documented through epidemiological studies that DHF is most likely to result from a secondary heterologous infection, and that individuals experiencing a DENV-2 or DENV-3 infection typically are more likely to present with more severe dengue disease than those individuals experiencing a DENV-1 or DENV-4 infection. However, a mechanistic understanding of how these risk factors affect disease outcomes, and further, how the virus's ability to evolve these mechanisms will affect disease severity patterns over time, is lacking. In the second chapter of my dissertation, I formulate mechanistic mathematical models of primary and secondary dengue infections that describe how the dengue virus interacts with the immune response and the results of this interaction on the risk of developing severe dengue disease. I show that only the innate immune response is needed to reproduce characteristic features of a primary infection whereas the adaptive immune response is needed to reproduce characteristic features of a secondary dengue infection. I then add to these models a quantitative measure of disease severity that assumes immunopathology, and analyze the effectiveness of virological indicators of disease severity. In the third chapter of my dissertation, I then statistically fit these mathematical models to viral load data of dengue patients to understand the mechanisms that drive variation in viral load. I specifically consider the roles that immune status, clinical disease manifestation, and serotype may play in explaining viral load variation observed across the patients. With this analysis, I show that there is statistical support for the theory of antibody dependent enhancement in the development of severe disease in secondary dengue infections and that there is statistical support for serotype-specific differences in viral infectivity rates, with infectivity rates of DENV-2 and DENV-3 exceeding those of DENV-1. In the fourth chapter of my dissertation, I integrate these within-host models with a vector-borne epidemiological model to understand the potential for virulence evolution in dengue. Critically, I show that dengue is expected to evolve towards intermediate virulence, and that the optimal virulence of the virus depends strongly on the number of serotypes that co-circulate. Together, these dissertation chapters show that dengue viral load dynamics provide insight into the within-host mechanisms driving differences in dengue disease patterns and that these mechanisms have important implications for dengue virulence evolution.
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As the world population continues to grow past seven billion people and global challenges continue to persist including resource availability, biodiversity loss, climate change and human well-being, a new science is required that can address the integrated nature of these challenges and the multiple scales on which they are manifest. Sustainability science has emerged to fill this role. In the fifteen years since it was first called for in the pages of Science, it has rapidly matured, however its place in the history of science and the way it is practiced today must be continually evaluated. In Part I, two chapters address this theoretical and practical grounding. Part II transitions to the applied practice of sustainability science in addressing the urban heat island (UHI) challenge wherein the climate of urban areas are warmer than their surrounding rural environs. The UHI has become increasingly important within the study of earth sciences given the increased focus on climate change and as the balance of humans now live in urban areas.
In Chapter 2 a novel contribution to the historical context of sustainability is argued. Sustainability as a concept characterizing the relationship between humans and nature emerged in the mid to late 20th century as a response to findings used to also characterize the Anthropocene. Emerging from the human-nature relationships that came before it, evidence is provided that suggests Sustainability was enabled by technology and a reorientation of world-view and is unique in its global boundary, systematic approach and ambition for both well being and the continued availability of resources and Earth system function. Sustainability is further an ambition that has wide appeal, making it one of the first normative concepts of the Anthropocene.
Despite its widespread emergence and adoption, sustainability science continues to suffer from definitional ambiguity within the academe. In Chapter 3, a review of efforts to provide direction and structure to the science reveals a continuum of approaches anchored at either end by differing visions of how the science interfaces with practice (solutions). At one end, basic science of societally defined problems informs decisions about possible solutions and their application. At the other end, applied research directly affects the options available to decision makers. While clear from the literature, survey data further suggests that the dichotomy does not appear to be as apparent in the minds of practitioners.
In Chapter 4, the UHI is first addressed at the synoptic, mesoscale. Urban climate is the most immediate manifestation of the warming global climate for the majority of people on earth. Nearly half of those people live in small to medium sized cities, an understudied scale in urban climate research. Widespread characterization would be useful to decision makers in planning and design. Using a multi-method approach, the mesoscale UHI in the study region is characterized and the secular trend over the last sixty years evaluated. Under isolated ideal conditions the findings indicate a UHI of 5.3 ± 0.97 °C to be present in the study area, the magnitude of which is growing over time.
Although urban heat islands (UHI) are well studied, there remain no panaceas for local scale mitigation and adaptation methods, therefore continued attention to characterization of the phenomenon in urban centers of different scales around the globe is required. In Chapter 5, a local scale analysis of the canopy layer and surface UHI in a medium sized city in North Carolina, USA is conducted using multiple methods including stationary urban sensors, mobile transects and remote sensing. Focusing on the ideal conditions for UHI development during an anticyclonic summer heat event, the study observes a range of UHI intensity depending on the method of observation: 8.7 °C from the stationary urban sensors; 6.9 °C from mobile transects; and, 2.2 °C from remote sensing. Additional attention is paid to the diurnal dynamics of the UHI and its correlation with vegetation indices, dewpoint and albedo. Evapotranspiration is shown to drive dynamics in the study region.
Finally, recognizing that a bridge must be established between the physical science community studying the Urban Heat Island (UHI) effect, and the planning community and decision makers implementing urban form and development policies, Chapter 6 evaluates multiple urban form characterization methods. Methods evaluated include local climate zones (LCZ), national land cover database (NCLD) classes and urban cluster analysis (UCA) to determine their utility in describing the distribution of the UHI based on three standard observation types 1) fixed urban temperature sensors, 2) mobile transects and, 3) remote sensing. Bivariate, regression and ANOVA tests are used to conduct the analyses. Findings indicate that the NLCD classes are best correlated to the UHI intensity and distribution in the study area. Further, while the UCA method is not useful directly, the variables included in the method are predictive based on regression analysis so the potential for better model design exists. Land cover variables including albedo, impervious surface fraction and pervious surface fraction are found to dominate the distribution of the UHI in the study area regardless of observation method.
Chapter 7 provides a summary of findings, and offers a brief analysis of their implications for both the scientific discourse generally, and the study area specifically. In general, the work undertaken does not achieve the full ambition of sustainability science, additional work is required to translate findings to practice and more fully evaluate adoption. The implications for planning and development in the local region are addressed in the context of a major light-rail infrastructure project including several systems level considerations like human health and development. Finally, several avenues for future work are outlined. Within the theoretical development of sustainability science, these pathways include more robust evaluations of the theoretical and actual practice. Within the UHI context, these include development of an integrated urban form characterization model, application of study methodology in other geographic areas and at different scales, and use of novel experimental methods including distributed sensor networks and citizen science.
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A constructivist philosophy underlies the Irish primary mathematics curriculum. As constructivism is a theory of learning its implications for teaching need to be addressed. This study explores the experiences of four senior class primary teachers as they endeavour to teach mathematics from a constructivist-compatible perspective with primary school children in Ireland over a school-year period. Such a perspective implies that children should take ownership of their learning while working in groups on tasks which challenge them at their zone of proximal development. The key question on which the research is based is: to what extent will an exposure to constructivism and its implications for the classroom impact on teaching practices within the senior primary mathematics classroom in both the short and longer term? Although several perspectives on constructivism have evolved (von Glaserfeld (1995), Cobb and Yackel (1996), Ernest (1991,1998)), it is the synthesis of the emergent perspective which becomes pivotal to the Irish primary mathematics curriculum. Tracking the development of four primary teachers in a professional learning initiative involving constructivist-compatible approaches necessitated the use of Borko’s (2004) Phase 1 research methodology to account for the evolution in teachers’ understanding of constructivism. Teachers’ and pupils’ viewpoints were recorded using both audio and video technology. Teachers were interviewed at the beginning and end of the project and also one year on to ascertain how their views had evolved. Pupils were interviewed at the end of the project only. The data were analysed from a Jaworskian perspective i.e. using the categories of her Teaching Triad of management of learning, mathematical challenge and sensitivity to students. Management of learning concerns how the teacher organises her classroom to maximise learning opportunities for pupils. Mathematical challenge is reminiscent of the Vygotskian (1978) construct of the zone of proximal development. Sensitivity to students involves a consciousness on the part of the teacher as to how pupils are progressing with a mathematical task and whether or not to intervene to scaffold their learning. Through this analysis a synthesis of the teachers’ interpretations of constructivist philosophy with concomitant implications for theory, policy and practice emerges. The study identifies strategies for teachers wishing to adopt a constructivist-compatible approach to their work. Like O’Shea (2009) it also highlights the likely difficulties to be experienced by such teachers as they move from utilising teacher-dominated methods of teaching mathematics to ones in which pupils have more ownership over their learning.
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This research aims to explore the challenges nurses face, when caring for stroke patients on a general medical/surgical ward, in the acute care setting and identify how nurses resolve or process this challenge. Healthcare environments continue to face the pressures of constraints such as reduced staffing levels, budgets, resources and less time, which influence care provision. Patient safety is central in care provision where nurses face the challenge of delivering best quality care when working within constraints. The incidence of stroke is increasing worldwide and internationally stroke units are the recognised minimum standard of care. In Ireland with few designated stroke units in operation many stroke patients are cared for in the acute general care setting. A classic grounded theory methodology was utilised for this study. Data was collected and analysed simultaneously through coding, constant comparison, theoretical sampling and memoing. Individual unstructured interviews with thirty two nurses were carried out. Twenty hours of non-participant observations in the acute general care setting were undertaken. The main concern that emerged was working within constraints. This concern is processed by nurses through resigning which consists of three phases; idealistic striving, resourcing and care accommodation. Through the process of resigning nurses engage in an energy maintenance process enabling them to continue working within constraints. The generation of the theory of resigning explains how nurses’ resolve or process working within constraints. This theory adds to the body of knowledge on stroke care provision. This theory has the potential to enhance nursing care, minimise burnout and make better use of resources while advocating for best care of stroke patients.
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English has been taught as a core and compulsory subject in China for decades. Recently, the demand for English in China has increased dramatically. China now has the world’s largest English-learning population. The traditional English-teaching method cannot continue to be the only approach because it merely focuses on reading, grammar and translation, which cannot meet English learners and users’ needs (i.e., communicative competence and skills in speaking and writing). This study was conducted to investigate if the Picture-Word Inductive Model (PWIM), a new pedagogical method using pictures and inductive thinking, would benefit English learners in China in terms of potential higher output in speaking and writing. With the gauge of Cognitive Load Theory (CLT), specifically, its redundancy effect, I investigated whether processing words and a picture concurrently would present a cognitive overload for English learners in China. I conducted a mixed methods research study. A quasi-experiment (pretest, intervention for seven weeks, and posttest) was conducted using 234 students in four groups in Lianyungang, China (58 fourth graders and 57 seventh graders as an experimental group with PWIM and 59 fourth graders and 60 seventh graders as a control group with the traditional method). No significant difference in the effects of PWIM was found on vocabulary acquisition based on grade levels. Observations, questionnaires with open-ended questions, and interviews were deployed to answer the three remaining research questions. A few students felt cognitively overloaded when they encountered too many writing samples, too many new words at one time, repeated words, mismatches between words and pictures, and so on. Many students listed and exemplified numerous strengths of PWIM, but a few mentioned weaknesses of PWIM. The students expressed the idea that PWIM had a positive effect on their English teaching. As integrated inferences, qualitative findings were used to explain the quantitative results that there were no significant differences of the effects of the PWIM between the experimental and control groups in both grade levels, from four contextual aspects: time constraints on PWIM implementation, teachers’ resistance, how to use PWIM and PWIM implemented in a classroom over 55 students.
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The integration of mathematics and science in secondary schools in the 21st century continues to be an important topic of practice and research. The purpose of my research study, which builds on studies by Frykholm and Glasson (2005) and Berlin and White (2010), is to explore the potential constraints and benefits of integrating mathematics and science in Ontario secondary schools based on the perspectives of in-service and pre-service teachers with various math and/or science backgrounds. A qualitative and quantitative research design with an exploratory approach was used. The qualitative data was collected from a sample of 12 in-service teachers with various math and/or science backgrounds recruited from two school boards in Eastern Ontario. The quantitative and some qualitative data was collected from a sample of 81 pre-service teachers from the Queen’s University Bachelor of Education (B.Ed) program. Semi-structured interviews were conducted with the in-service teachers while a survey and a focus group was conducted with the pre-service teachers. Once the data was collected, the qualitative data were abductively analyzed. For the quantitative data, descriptive and inferential statistics (one-way ANOVAs and Pearson Chi Square analyses) were calculated to examine perspectives of teachers regardless of teaching background and to compare groups of teachers based on teaching background. The findings of this study suggest that in-service and pre-service teachers have a positive attitude towards the integration of math and science and view it as valuable to student learning and success. The pre-service teachers viewed the integration as easy and did not express concerns to this integration. On the other hand, the in-service teachers highlighted concerns and challenges such as resources, scheduling, and time constraints. My results illustrate when teachers perceive it is valuable to integrate math and science and which aspects of the classroom benefit best from the integration. Furthermore, the results highlight barriers and possible solutions to better the integration of math and science. In addition to the benefits and constraints of integration, my results illustrate why some teachers may opt out of integrating math and science and the different strategies teachers have incorporated to integrate math and science in their classroom.
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Given the importance of gender in consumer research, one might expect feminist perspectives to be at the forefront of critical engagement with consumer behaviour theory. However, in recent years, feminist voices have been barely audible. This paper explores the value of, and insights offered by, feminist theories and feminist activism, and how feminist theory and practice has altered our understanding of gendered consumption. It then argues that postmodern and postfeminist perspectives have diluted feminism's transformative potential, leading to a critical impasse in marketing and consumer research. In conclusion, we suggest that feminist perspectives, notably materialist feminism, might open up fresh new possibilities for critique, and interesting and worthwhile areas for transformative research in consumer behaviour.
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Syria has been a major producer and exporter of fresh fruit and vegetables (FFV) in the Arabic region. Prior to 2011, Syrian FFV were mainly exported to the neighbouring countries, the Gulf States and Northern Africa as well as to Eastern European countries. Although the EU is potentially one of the most profitable markets of high quality FFV (such as organic ones) in the world, Syrian exports of FFV to Western European countries like Germany have been small. It could be a lucrative opportunity for Syrian growers and exporters of FFV to export organic products to markets such as Germany, where national production is limited to a few months due to climatic conditions. Yet, the organic sector in Syria is comparatively young and only a very small area of FFV is certified according to EU organic regulations. Up to the author’s knowledge, little was known about Syrian farmers’ attitudes towards organic FFV production. There was also no study so far that explored and analysed the determining factors for organic FFV adoption among Syrian farmers as well as the exports of these products to the EU markets. The overarching aim of the present dissertation focused on exploring and identifying the market potential of Syrian exports of organic FFV to Germany. The dissertation was therefore concerned with three main objectives: (i) to explore if German importers and wholesalers of organic FFV see market opportunities for Syrian organic products and what requirements in terms of quality and quantity they have, (ii) to determine the obstacles Syrian producers and exporters face when exporting agricultural products to Germany, and (iii) to investigate whether Syrian farmers of FFV can imagine converting their farms to organic production as well as the underlying reasons why they do so or not. A twofold methodological approach with expert interviews and a farmer survey were used in this dissertation to address the abovementioned objectives. While expert interviews were conducted with German and Syrian wholesalers of (organic) FFV in 2011 (9 interviews each), the farmer survey was administrated with 266 Syrian farmers of FFV in the main region for the production of FFV (i.e. the coastal region) from November 2012 till May 2013. For modelling farmers’ decisions to adopt organic farming, the Theory of Planned Behaviour as theoretical framework and Partial Least Squares Structural Equation Modelling as the main method for data analysis were used in this study. The findings of this dissertation yield implications for the different stakeholders (governmental institutions and NGOs, farmers, exporters, wholesalers, etc.) who are interested in prompting the Syrian export of organic products. Based on the empirical results and a literature review, an action plan to promote Syrian production and export of organic products was developed which can help in the post-war period in Syria at improving the organic sector.
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Selon la théorie de l’auto-détermination, l’autonomie est un besoin universel de base qui, lorsque soutenu, permet aux individus de mieux fonctionner et de vivre plus de bien-être psychologique (p. ex., Deci & Ryan, 2008). Le style parental des parents qui soutiennent l’autonomie de leur enfant est caractérisé par le soutien du fonctionnement autodéterminé de ce dernier. Sa définition traditionnelle inclut des pratiques telles qu’offrir des explications et des choix lors des requêtes, communiquer de l’empathie, et encourager les prises d’initiatives tout en minimisant l’utilisation d’un langage contrôlant (p. ex., Soenens et al., 2007). Les bénéfices d’un style parental qui soutient l’autonomie d’un enfant ont été bien documentés (p. ex., Grolnick, Deci, & Ryan, 1997), toutefois, peu d’études ont été effectuées auprès des bambins. Or, cette thèse visait à enrichir la littérature sur le « parentage » en explorant les pratiques soutenantes qui sont utilisées par des parents de bambins dans un contexte de socialisation (étude 1), ainsi qu’en examinant les facteurs qui peuvent brimer leur mise en pratique (étude 2). La première étude a examiné un grand nombre de pratiques de socialisation que les parents qui favorisent davantage le soutien à l’autonomie (SA) pourraient utiliser plus fréquemment lorsqu’ils font des demandes à leurs bambins. Cette étude nous a permis d’explorer comment les parents manifestent leur SA et si le SA dans ce type de contexte est associé à un plus grand niveau d’internalisation des règles. Des parents (N = 182) de bambins (M âge = 27.08 mois) ont donc été invités à rapporter la fréquence avec laquelle ils utilisent 26 pratiques potentiellement soutenantes lorsqu’ils demandent à leurs bambins de compléter des tâches importantes mais non intéressantes et de rapporter à quel point ils valorisent le SA. Huit pratiques ont été identifiées comme étant soutenantes: quatre façons de communiquer de l’empathie, donner des explications courtes, expliquer pourquoi la tâche est importante, décrire le problème de façon informative et neutre, et mettre en pratique le comportement désiré soi-même. De plus, l’ensemble des huit pratiques corrélait positivement avec le niveau d’internalisation des bambins, suggérant aussi que celles-ci représentent bien le concept du SA. Des études futures pourraient tenter de répliquer ces résultats dans des contextes potentiellement plus chargés ou ébranlants (p. ex., réagir face à des méfaits, avec des enfants souffrant de retard de développement). La deuxième étude a poursuivi l’exploration du concept du SA parental en examinant les facteurs qui influencent la fréquence d’utilisation des stratégies soutenantes dans des contextes de socialisation. Puisque la littérature suggère que le stress parental et le tempérament difficile des bambins (c.-à-d., plus haut niveau d’affectivité négative, plus faible niveau de contrôle volontaire/autorégulation, plus faible niveau de surgency) comme étant des facteurs de risque potentiels, nous avons exploré de quelle façon ces variables étaient associées à la fréquence d’utilisation des stratégies soutenantes. Les buts de l’étude étaient: (1) d’examiner comment le tempérament des bambins et le stress parental influençaient le SA parental, et (2) de vérifier si le stress parental médiait la relation possible entre le tempérament des bambins et le SA parental. Le même échantillon de parents a été utilisé. Les parents ont été invités à répondre à des questions portant sur le tempérament de leur enfant ainsi que sur leur niveau de stress. Les résultats ont démontré qu’un plus grand niveau d’affectivité négative était associé à un plus grand niveau de stress parental, qui à son tour prédisait moins de SA parental. De plus, le stress parental médiait la relation positive entre l’autorégulation du bambin et le SA parental. Des recherches futures pourraient évaluer des interventions ayant pour but d’aider les parents à préserver leur attitude soutenante durant des contextes de socialisation plus difficiles malgré certaines caractéristiques tempéramentales exigeantes des bambins, en plus du stress qu’ils pourraient vivre au quotidien.
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The phenomenon of patterned distribution of pH near the cell membrane of the algae Chara corallina upon illumination is well-known. In this paper, we develop a mathematical model, based on the detailed kinetic analysis of proton fluxes across the cell membrane, to explain this phenomenon. The model yields two coupled nonlinear partial differential equations which describe the spatial dynamics of proton concentration changes and transmembrane potential generation. The experimental observation of pH pattern formation, its period and amplitude of oscillation, and also its hysteresis in response to changing illumination, are all reproduced by our model. A comparison of experimental results and predictions of our theory is made. Finally, a mechanism for pattern formation in Chara corallina is proposed.
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Since Bowlby devised his theory of attachment, originally for clinical purposes, refinements and extensions have developed its clinical utility. The research question asked how experienced contemporary clinicians now perceive the role of attachment in the formulation and treatment of distress by reference to their clinical work. Using grounded theory methodology, underpinned by a relativist, moderate social constructionist epistemology, initial sampling consisted of 16 in-depth interviews with experienced clinicians. The tentative theoretical categories that emerged were then developed in theoretical sampling in further interviews with 5 of the initial interviewees. The final theoretical categories to emerge concerned the prevalence of caregiver-related problems, the provision of safety together with the prioritisation of the relationship with self as attachment-related treatment strategies, and attachment theory’s provision of understanding in problem formulation. Whilst this suggests that attachment-related ideas are integrated in contemporary practice, it also suggests that the clinical utility now offered by attachment theory, as established in the literature, has not found broad appeal amongst clinicians despite the commonness of attachment-related presenting problems. The implications of this are manifold. To begin with, attachment theorists have largely failed to bring the potential now offered by attachment-related therapeutic interventions to the market. This situation makes it incumbent on the next generation of attachment researchers to more clearly articulate techniques with which clinicians, of whatever theoretical orientation, can better leverage attachment-related knowledge in their clinical work. In this enterprise, perhaps the knowledge and experience of expert clinicians could be harvested, as this research has done. Moreover, researchers must expand the evidence base that such interventions actually work. Beyond the implications for clinical utility and efficacy, the findings strengthen counselling psychology’s influence on society’s perception and treatment of attachment-related problems.
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Silicon carbide (SiC) is a promising material for electronics due to its hardness, and ability to carry high currents and high operating temperature. SiC films are currently deposited using chemical vapor deposition (CVD) at high temperatures 1500–1600 °C. However, there is a need to deposit SiC-based films on the surface of high aspect ratio features at low temperatures. One of the most precise thin film deposition techniques on high-aspect-ratio surfaces that operates at low temperatures is atomic layer deposition (ALD). However, there are currently no known methods for ALD of SiC. Herein, the authors present a first-principles thermodynamic analysis so as to screen different precursor combinations for SiC thin films. The authors do this by calculating the Gibbs energy ΔGΔG of the reaction using density functional theory and including the effects of pressure and temperature. This theoretical model was validated for existing chemical reactions in CVD of SiC at 1000 °C. The precursors disilane (Si2H6), silane (SiH4), or monochlorosilane (SiH3Cl) with ethyne (C2H2), carbontetrachloride (CCl4), or trichloromethane (CHCl3) were predicted to be the most promising for ALD of SiC at 400 °C.
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Sammelrezension von: 1. Edward W. Taylor / Patricia Cranton, and Associates (Hrsg.): The Handbook of Transformative Learning, Theory, Research, and Practice, San Francisco, CA: Jossey-Bass 2012 (598 S.; ISBN 978-1-111-21891-4) 2. Jack Mezirow / Edward W. Taylor, and Associates (Hrsg.): Transformative Learning in Practice, Insights from Community, Workplace, and Higher Education, San Francisco, CA: Jossey-Bass 2009 (303 S.; ISBN 978-0-470-25790-6)