4242 research outputs found
Sort by
Sediment reworking mechanisms in shelf seas : In situ observations from the southeastern North Sea
Get PDFThe seafloor in shallow coastal and shelf seas is a highly dynamic system providing plenty of natural resources and important ecosystem services. Driven by energetic physical forcing, biological activity and intense anthropogenic use, its mobile sediments are constantly overturned. The reworking processes mediate the exchange of abundant organic matter and pollutants across the benthic interface. Coherent in situ measurements of forcing and morphodynamic response help to identify relevant reworking mechanisms, to outline their spatial and temporal scales, and to quantify their impacts on the benthic ecosystem. New high-resolution observation techniques enable also the assessment of small-scale processes that, due to their ubiquity, are yet of shelf-wide importance. This thesis explores three mechanisms in the southeastern North Sea: The morphology and dynamics of small scale-bedforms, the relation of physical and biogenic sediment reworking by bedform migration and bioturbation, and the effect of submarine fluid expulsion. The analysis of these processes reveals new links between physical and biological drivers and illustrates their complex interactions at the benthic interface
Self-Consistent Modelling of Non-Thermal Atmospheric Argon Plasma During Arc Discharge and Its Interaction with Metal Electrodes
Get PDFHeat transfer processes associated with arc plasmas are important for many industrial applications such as electric propulsion, plasma spray and arc welding. In these applications, an electric arc is used because it offers high energy densities and a controlled environment. However, it is sometimes not realizable or not economic to get the parameters within the high temperature region of plasma precisely by means of experimental measurements. A numerical model that offers reliable description of discharging process is a good choice. Any model of arc plasmas must contain not only the conservation of mass, momentum and energy, but also electromagnetic description that follows Maxwella s equations. Since the last 30 years, intensive researches embarking on nonequilibrium plasmas have led to fruitful achievements, among them NLTE (non-Local Thermal Equilibrium) model plays an important role in numerical modelling due to its superiority over LTE (Local Thermal Equilibrium) model in accounting for the difference of two phase temperatures (heavy species and electrons) that cannot be neglected near electrodes. However, deeper researches meet obstacles when the discharging system needs to be simulated self-consistently as a whole and with as few presumed conditions as possible. On one hand, discharging under high current operation tends to overheat its electrodes leading to melting or evaporating, particles from electrode material that enter the plasma will change its composition and the heat transfer process. On the other hand, therea s still a a mysteriousa region whose physical structure is so different from the main arc plasma region that cannot be accounted by conventional transport equations or theories without any extra treatments for it. This region, sometimes called sheath layer or space-charge layer, plays an important role in bridging the thermal and electric energy of arc column to electrodes. To develop a reasonable model in this region and make it compatible with the two other regions will extend the applicability of CFD model in discharging devices. The motivation of this doctoral thesis is based on my special interest in sheath region, or in other words, my pursuit of developing a self-consistent model that is capable of solving the whole plasma-electrode system. Concerning the complexity of sheath, no secondary physical phenomena such as melting and evaporating are considered in this study. For the main arc region, the plasma composition is calculated based on species conservation equations that consider both diffusion and production/loss activities of particles. And for the sake of high temperature of plasma core, ionization up to third level is applied. In the sheath layer, the effective sheath electrical conductivity is utilized, which is based on the assumption of Childa s collisionless sheath and Lowkea s expression. The ionization degree of plasma sheath plays an important role in this self-consistent method. To validate the model proposed here, several simple benchmark simulations are made and the numerical results concerning temperature, velocity and magnetic field yield satisfactory agreements with experimental or theoretical results. With the model being validated, a D.C. non-transferred plasma torch is studied. The total voltages of both situations are compared with experimental measurements. It shows that the sheath model developed in this scope make the numerical results closer to reality and is responsible for the strong fluctuation of arc jets, which also makes cathode surface temperature fluctuate accordingly. Finally, pros and cons of some new design patterns of plasma torches are discussed, with the multi anode/single cathode type DeltaGun simulated for the comparison of performances with the original type. It reveals that such kind of configuration helps to damp the unwanted arc fluctuation with multiple arc roots. It is also numerically confirmed that when an external coil is added around anode to produce a proper magnetic field, the temperature of anode attachment can be reduced due to enhanced circumferential movement of arc roots by Lorentz force, which lowers the possibility of erosion and promotes a longer lifetime
Book Review: Internationalization in Vocational Education and Training
Get PDFThe book was published in the series Technical and Vocational Education and Training: Issues, Concerns and Prospects. Series Editor-in-Chief is Rupert MacLean. Editors of the volume are Ly Thi Tran, associate professor in the Faculty of Arts and Education of Deakin University in Australia), and Kate Dempsey, independent education consultant from Melbourne in Australia
Ecological lubrication in cold forming of sintered powder metallurgical components
Get PDFIn this contribution a new lubrication approach for cold bulk metal forming is presented. By exploiting the process-related porosity of pm components as a lubricant storage, the resulting pressure of a forming process forces the stored oil to leak out lubricating the process. As a result advantages like a decrease of process time because of the lubrication step omission, and an increased deformability due to compensation of lubricating film break are expected. In addition, conversion coating, which have a negative environmental impact but are commonly used in cold bulk metal forming, can be avoided. Besides that, the porosity of the pm component is reduced leading to improved mechanical properties. Experimental investigations with cylindrical aluminium pm components were carried out by compression tests in de-pendence of initial porosity, impregnation time and lubricant. The oil saturation of all samples could be reached after 4400 min impregnation time. The relative density has an inversely proportional effect on the absolute and the relative impregnated oil quantity. The compression tests showed an increasing maximum load with decreasing oil quantity and rising relative density. Moreover, the loads determined in the reference tests tend to be greater in comparison to the novel lubrication method
Dynamics of Neuronal Interactions in the Visual Cortex of Macaca Mulatta
Get PDFThis work is dedicated to studying the effects of attention which result in measurable changes in the functioning of single neurons and neuronal populations. A special emphasis lies on establishing a suitable method of recording from multiple neuronal populations in the visual cortex of a behaving monkey, as well as on analyzing the acquired signals. A chronically implanted large-area electrode array was used for epidural recording of brain potentials. Additionally, two electrode arrays for large-area chronic intracortical recording were designed, manufactured, and successfully implemented on a macaque monkey. By this means, local field potentials were recorded from different neuronal populations in two visual areas of a macaque monkey as he performed a shape-tracking task presented in front of him on a screen. Two kinds of stimulus-driven neuronal response in areas V1 and V4 were acquired: with the stimulus being behaviorally relevant and hence lying within the locus of the monkeya s attention, and with the stimulus being ignored and hence lying outside the locus of the monkeya s attention. Comparing the two response types provided a clue to the differences in neuronal processing of attended and non-attended stimuli. According to the working hypothesis, oscillatory responses generated in different neuronal populations by an attended stimulus would be synchronized in the gamma frequency band. To test this hypothesis, the acquired brain potentials were wavelet transformed and oscillatory power of different neuronal populations as well as phase coherence between them was computed. The results revealed a high degree of phase coherence in the gamma frequency band between oscillatory responses of neuronal populations in areas V1 and V4 representing the attended stimulus. A non-attended stimulus, however, produced non-phase-locked oscillatory responses in areas V1 and V4. The results presented here supported the working hypothesis, and the gamma-band synchronization was suggested to provide the mechanism of attention which enhances the processing of behaviorally relevant stimuli
Diversity and function of microbial communities in the Arctic Ocean
Get PDFThe Arctic Ocean ecosystem is rapidly changing in response to climate warming. The ongoing decline of its sea-ice cover has raised many questions as to the ecological consequences on biodiversity, primary productivity, and the biological carbon pump. The diversity and function of bacterial communities in the Arctic Ocean has been little explored, despite their often important role in biogeochemical cycling. One objective of this thesis was therefore to improve the current knowledge of microbial community diversity in the most understudied region of the Arctic Ocean, the deep central Eurasian basin. As sea-ice reduction is altering primary productivity and biological transport processes from the surface ocean to the deep sea, another focus of this thesis was the identification of bacterial groups associated to freshly formed, sinking and deposited particulate organic matter. Finally, the underlying genomic features that deep-sea surface sediment bacteria use for carbon turnover were analyzed, as the degradation of organic matter by heterotrophic bacteria in deep-sea sediments regulates the efficiency of CO2 removal from the atmosphere over geological time scales
Conservative Extensions and Satisfiability in Fragments of First-Order Logic : Complexity and Expressive Power
Get PDFIn this thesis, we investigate the decidability and computational complexity of (deductive) conservative extensions in expressive fragments of first-order logic, such as two-variable and guarded fragments. Moreover, we also investigate the complexity of (query) conservative extensions in Horn description logics with inverse roles. Aditionally, we investigate the computational complexity of the satisfiability problem in the unary negation fragment of first-order logic extended with regular path expressions. Besides complexity results, we also study the expressive power of relation-changing modal logics. In particular, we provide translations intto hybrid logic and compare their expressive power using appropriate notions of bisimulations
Decision-Making Processes Among Potential Dropouts in Vocational Education and Training and Adult Learning
Get PDFContext: Aiming at gaining knowledge about students' thoughts and actions in deciding to stay in or drop out of an educational programme, an empirical study was conducted on dropout among 18-24-year-old students in VET and basic general adult learning. Approach: In order to pursue this aim, the study combined two sets of data: weekly student surveys and interviews with these same students. While the surveys provide a weekly snapshot of the students' thoughts regarding the probability of them continuing in the programme, their satisfaction with the educational programme as a whole, the specific lessons they attend, and the atmosphere at the school, the interviews contribute with detailed descriptions of the students' thoughts on the same matters. Findings: Based on the students' answers over an eight-week period, it was possible to trace a graph illustrating changes in the students' attitudes. These graphs can be placed within four categories of development: the stable, the positive, the unstable, and the negative. The latter can furthermore be differentiated as reflecting a stable decline, a fluctuating decline, or a sudden decline. In the interviews, the aim was to elicit the individual students' thoughts and actions at the points when their graphs took a turn. Conclusions: The findings show that the students' thoughts and actions concern matters both inside and outside the school. Furthermore, seemingly trivial matters in the students' lives are shown to have a potentially decisive influence on the students' thoughts about staying in or dropping out of a programme. These findings confirm the importance of focusing on students' decision-making processes in research on dropout. However, further research is needed to increase understanding of processes leading to decisions to drop out of education, including the qualification of methods to capture these processes
The Experiences of Learners with Disabilities in Mainstream Vocational Training in Nepal
Get PDFContext: This article explores the lived experiences of learners with disabilities who were attending short-term skills-based training programs in Nepal. The research questions addressed were how the learners with disabilities had been experiencing learning with their peers without disabilities and whether the vocational training was inclusive from the perspectives of learners with disabilities. Approach: Based on a phenomenological design, eight learners with disabilities were purposively selected. In-depth interviews were held with the participants. Data were collected in the forms of audiotaped recordings, field notes, and institutional records. The thematic analysis technique was employed to explicate the transcribed data. Results: The results showed that learners with disabilities faced difficulty in commuting to and from the training center. The physical learning environment was insufficiently accessible, and this affected the learning of students with disabilities. Although the learners with physical disabilities had no problem in understanding the subject matter taught in the mainstream classrooms, the learners with visual impairments and those who were with hard of hearing had, at times, difficulty in following their instructors. The learners with disabilities had trouble with socialization and with forming friendships though they had supportive instructors. The participants' statements revealed that the existing inclusion practices were not enough to address the needs of persons with disabilities. However, they viewed inclusion as a much better option to cater to the needs of differently abled people. Conclusion: Inclusive technical and vocational education and training (TVET) is in practice throughout the world. This qualitative research paper has presented the perspectives of learners with disabilities (LWDs) about the inclusive practices in the Nepalese TVET sector. More importantly, this study has given a voice to the LWDs from mainstream vocational training centers in Nepal
GlücksErlebnis: Können Glückspädagogik und Erlebnispädagogik Hand in Hand gehen ? - Eine Untersuchung möglicher Perspektiven
Get PDFDie vorliegende Bachelorthesis hat zum Ziel die Gemeinsamkeiten der Glückspädagogik und Erlebnispädagogik, sowie mögliche Perspektiven für eine Verknüpfung der beiden pädagogischen Ansätze darzulegen. Anhand einer reinen Literaturanalyse wird die Grundlage gebildet in der Auseinandersetzung mit der Glückpsychologie und Positiven Psychologie; darauf auf- bauend die Positive Pädagogik und Glückspädagogik auf der einen Seite, und die Erlebnispädagogik als gegenüberstehende Theorie auf der anderen Seite. Im anschließenden Vergleich der Gemeinsamkeiten und Unterschiede wird bestätigt, dass es viele Schnittstellen gibt. Insbesondere die Persönlichkeitsentwicklung und Stärkung der eigenen Kompetenzen, welche junge Menschen dazu befähigen sollen, ein gelingendes Leben mit hohem Wohlbefinden zu führen, sind als beiderseitiges Ziel festzuhalten. Weitere Ähnlichkeiten im Anbetracht des entwicklungshistorischen, und pädagogischen Hintergrunds konnten gefunden werden. Schließlich wurden drei Möglichkeiten für die Verknüpfung erarbeitet. Da das Thema in dieser Symbiose bisher wenig bearbeitet ist, erhofft sich der Autor einen interdisziplinären Erkenntnisgewinn, aus dem sich möglicherweise in Zukunft ein neues Programm entwickeln lässt