| 1. |
- Andersson, Henric, 1963-
(författare)
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Aircraft Systems Modeling : Model Based Systems Engineering in Avionics Design and Aircraft Simulation
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aircraft developers like other development and manufacturing companies, are experiencing increasing complexity in their products and growing competition in the global market. One way to confront the challenges is to make the development process more efficient and to shorten time to market for new products/variants by using design and development methods based on models. Model Based Systems Engineering (MBSE) is introduced to, in a structured way, support engineers with aids and rules in order to engineer systems in a new way.In this thesis, model based strategies for aircraft and avionics development are studied. A background to avionics architectures and in particular Integrated Modular Avionics is described. The integrating discipline Systems Engineering, MBSE and applicable standards are also described. A survey on available and emerging modeling techniques and tools, such as Hosted Simulation, is presented and Modeling Domains are defined in order to analyze the engineering environment with all its vital parts to support an MBSE approach.Time and money may be saved by using modeling techniques that enable understanding of the engineering problem, state-of-the-art analysis and team communication, with preserved or increased quality and sense of control. Dynamic simulation is an activity increasingly used in aerospace, for several reasons; to prove the product concept, to validate stated requirements, and to verify the final implementation. Simulation is also used for end-user training, with specialized training simulators, but with the same underlying models. As models grow in complexity, and the set of simulation platforms is expanded, new needs for specification, model building and configuration support arise, which requires a modeling framework to be efficient.
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| 2. |
- Phuyal, Dibya, et al.
(författare)
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The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy
- 2018
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 6:20, s. 9498-9505
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth halide compounds as a non-toxic alternative are increasingly investigated because of their potential in optoelectronic devices and their rich structural chemistry. Hard X-ray spectroscopy was applied to the ternary bismuth halide Cs3Bi2I9 and its related precursors BiI3 and CsI to understand its electronic structure at an atomic level. We specifically investigated the core levels and valence band using X-ray photoemission spectroscopy (PES), high-resolution X-ray absorption (HERFD-XAS), and resonant inelastic X-ray scattering (RIXS) to get insight into the chemistry and the band edge properties of the two bismuth compounds. Using these element specific X-ray techniques, our experimental electronic structures show that the primary differences between the two bismuth samples are the position of the iodine states in the valence and conduction bands and the degree of hybridization with bismuth lone pair (6s(2)) states. The crystal structure of the two layered quasi-perovskite compounds plays a minor role in modifying the overall electronic structure, with variations in bismuth lone pair states and iodine band edge states. Density Functional Theory (DFT) calculations are used to compare with experimental data. The results demonstrate the effectiveness of hard X-ray spectroscopies to identify element specific bulk electronic structures and their use in optoelectronic devices.
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| 3. |
- Averfalk, Helge, 1988-
(författare)
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Enhanced District Heating Technology : Maintaining Future System Feasibility
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When heat demand and high temperature heat supply gradually decreases in the future, then it will effect district heating systems ability to compete on the heat market. A good way to mitigate less district heating feasibility is to operate systems with lower temperature levels and the most conceivable way to achieve lower temperature levels is to decrease return temperatures.Thus, this thesis emphasise temperature errors embedded in district heating systems. Only a selection of temperature errors are analysed in this thesis. First, the temperature error that occurs due to recirculation in distribution networks at low heat demands. Second, the temperature error that occurs due to hot water circulation in multi-family buildings. Third, the temperature error that occurs due to less than possible heat transfer in heat exchangers, i.e. too short thermal lengths.In order to address these temperature errors three technology changes have been proposed (i) three-pipe distribution network to separate the recirculation return flow from the delivery return flow, (ii) apartment substations to eliminate hot water circulation utilisation, and (iii) improved heat exchangers for lower return temperatures at a constant scenario. Analysis of proposed changes has resulted in annual average return temperatures between 17-21 °C.Furthermore, rapid introduction of intermittent renewable electricity supply in the energy system has prompted an increased necessity of power system balancing capacities. Large-scale conversion of power-to-heat in electric boilers and heat pumps is a feasible alternative to achieve such balancing capacities. Analysis of the unique Swedish experience with utilisation of large heat pumps installations connected to district heating systems show that since the 1980s 1527 MW of heat power has been installed, about 80 % of the capacity was still in use by 2013. Thus, a cumulative value of over three decades of operation and maintenance exists within Swedish district heating systems.The two papers presented in this thesis are related to future district heating systems through the five abilities of fourth generation district heating (4GDH), which are documented in the definition paper of 4GDH.
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| 4. |
- Höglund, Linda, 1974-
(författare)
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Growth and characterisation of InGaAs-based quantum dots-in-a-well infrared photodetectors
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents results from the development of quantum dot (QD) based infrared photodetectors (IPs). The studies include epitaxial growth of QDs, investigations of the structural, optical and electronic properties of QD-based material as well as characterisation of the resulting components.Metal-organic vapour phase epitaxy is used for growth of self-assembled indium arsenide (InAs) QDs on gallium arsenide (GaAs) substrates. Through characterisation by atomic force microscopy, the correlation between size distribution and density of quantum dots and different growth parameters, such as temperature, InAs deposition time and V/III-ratio (ratio between group V and group III species) is achieved. The V/III-ratio is identified as the most important parameter in finding the right growth conditions for QDs. A route towards optimisation of the dot size distribution through successive variations of the growth parameters is presented.The QD layers are inserted in In0.15Ga0.85As/GaAs quantum wells (QWs), forming so-called dots-in-a-well (DWELL) structures. These structures are used to fabricate IPs, primarily for detection in the long wavelength infrared region (LWIR, 8-14 μm).The electron energy level schemes of the DWELL structures are revealed by a combination of different experimental techniques. From Fourier transform photoluminescence (FTPL) and FTPL excitation (FTPLE) measurements the energy level schemes of the DWELL structures are deduced. Additional information on the energy level schemes is obtained from tunneling capacitance measurements and the polarization dependence studies of the interband transitions. From tunneling capacitance measurements, the QD electron energy level separation is confirmed to be 40-50 meV and from the polarization dependence measurements, the heavy hole character of the upper hole states are revealed.Further characterisation of the IPs, by interband and intersubband photocurrent measurements as well as dark current measurements, is performed. By comparing the deduced energy level scheme of the DWELL structure and the results of the intersubband photocurrent measurements, the origin of the photocurrent is determined. The main intersubband transition contributing to the photocurrent is identified as the QD ground state to a QW excited state transition. Optical pumping is employed to gain information on the origin of an additional photocurrent peak observed only at temperatures below 60 K. By pumping resonantly with transitions associated with certain quantum dot energy levels, this photocurrent peak is identified as an intersubband transition emanating from the quantum dot excited state. Furthermore, the detector response is increased by a factor of 10, when using simultaneous optical pumping into the quantum dots states, due to the increasing electron population created by the pumping. In this way, the potentially achievable responsivity of the detector is predicted to be 250 mA/W.Significant variations of photocurrent and dark currents are observed, when bias and temperature are used as variable parameters. The strong bias and temperature dependence of the photocurrent is attributed to the escape route from the final state in the QW, which is limited by tunneling through the triangular barrier. Also the significant bias and temperature dependence of the dark current could be explained in terms of the strong variation of the escape probability from different energy states in the DWELL structure, as revealed by interband photocurrent measurements. These results are important for the future optimisation of the DWELL IP.Tuning of the detection wavelength within the LWIR region is achieved by means of a varying bias across the DWELL structure. By positioning the InAs quantum dot layer asymmetrically in a 8 nm wide In0.15Ga0.85As/GaAs quantum well, a step-wise shift in the detection wavelength from 8.4 to 10.3 μm could be achieved by varying the magnitude and polarity of the applied bias. These tuning properties could be essential for applications such as odulators and dual-colour infrared detection.
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| 5. |
- Westerlund, Stina, 1968-
(författare)
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Lust och olust : elevers erfarenheter i textilslöjd
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the thesis is to investigate and analyse students’ expressions of pleasure and displeasure and how these are manifested in actions in the teaching of textile sloyd in lower secondary education. The study’s focus is on students’ expressions of pleasure and displeasure in social action in the working processes of textile sloyd and on how these expressions can be related to learning. The empirical material consists of observations, video and audio recordings, individual interviews and focus group interviews, where video and audio recordings were used as stimulated recall. In all, 32 lessons in textile sloyd and 49 students aged 14-15 years were observed at four different schools. Theoretically, the thesis is based on Mead’s practical intersubjectivity and on Dewey’s theory of experience-based learning and dependence on emotions and actions. Pleasure and displeasure constitute valuating partial aspects of emotions. Based on a socio-cultural perspective, emotions are regarded as practices which arise from different predispositions’ dependence on the social context. The study’s analytical approach is hermeneutical. Critical incidents regarding students’ expressions of pleasure and displeasure in social action found in observations and video and audio recordings were analysed in terms of Mead’s concept of gestures. The events were combined with what the students describe as critical incidents of pleasure and displeasure in the interviews and focus group talks. The material was then thematised. Several situations were then subjected to deeper analysis based on sociality and a change in perspective and related to different concepts of learning. The result of the thesis shows a tripartite semantic structure where students’ pleasure and displeasure in textile sloyd are mainly based on textile sloyd’s specific educational community, students’ relationship to the sloyd object and their experience of the working process. Social interaction, humour and mutual acknowledgement proved to be of importance for the function of pleasure and displeasure in the students’ working processes. The students’ experience of pleasure and displeasure depended on their control of the work, the characteristics of different craft techniques and their awareness of time. Pleasure and displeasure in textile sloyd found an expression in four overarching emotional practices with decisive importance for the students’ opportunities for learning: the repudiating, insecure, accepting and incorporating emotional practice. The study also provides an insight into how different cultural factors enable a certain scope for pleasure and displeasure. In this connection, social changes in relation to objects are discussed, as are changes in sociality and emotionality. Based on the pair of concepts of authenticity and ephemerality and closeness and intensity, cultural changes are visualised that are conceivably important for the students’ experiences of pleasure and displeasure in textile sloyd.
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