| 1. |
- Aghaeipour, Mahtab
(författare)
-
Tailoring the Optical Response of III-V Nanowire Arrays
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Semiconductor nanowires show a great deal of promise for applications in a wide range of important fields, including photovoltaics, biomedicine, and information technology. Developing these exciting applications is strongly dependent on understanding the fundamental properties of nanowires, such as their optical resonances and absorption spectra. In this thesis we explore optical absorption spectra of arrays of vertical III-V nanowires with a special emphasis on structures optimized to enhance absorption in the solar spectrum. First, we analyze experimentally determined absorption spectra of both indium phosphide (InP) and gallium phosphide (GaP) nanowire arrays. The study provides an intuitive understanding of how the observed absorption resonances in the nanowires may be tuned as a function of their geometrical parameters and crystal structure. As a consequence, the spectral position of absorption resonances can be precisely controlled through the nanowire diameter. However, the results highlight how the blue-shift in the optical absorption resonances as the diameter of the nanowires decreases comes to a halt at low diameters. The stop point is related to the behavior of the refractive indices of the nanowires. The wavelength of the stop is different for nanowire polytypes of similar dimensions due to differences in their refractive indices. We then present a theoretical argument that it is important to consider symmetry properties when tailoring the optical modes excited in the nanowires for enhanced absorption. We show that absorption spectra may be enhanced compared to vertical nanowires at normal incidence by tilting the nanowires with normal incidence light, or by using off-normal incidence with vertical nanowires. This is because additional optical modes inside the nanowires are excited when the symmetry is broken. Looking forward to omnidirectional applications, we consider branched nanowires as a way to enhance the absorption spectra at normal incidence by taking advantage of simultaneous excitation of the spectrally different optical modes in the branches and the stems. Third, we describe in theoretical terms how integrating distributed Bragg reflectors (DBRs) with the nanowires can improve absorption spectra compared to conventional nanowires. DBRs provide a way to employ light trapping mechanisms which increases the optical path length of the excited modes and thereby improves the absorption of the excited modes. At normal incidence, DBR-nanowires improve the absorption efficiency to 78%, compared to 72% for conventional nanowires. We show that the efficiency is increased to 85% for an off-normal incident angle of 50˚. Overall, our results show that studies of optical resonances in nanowires that take the light-matter interaction into account provide opportunities to develop novel optical and optoelectronic functionalities in nanoscience and nanotechnology.
|
|
| 2. |
- Nehler, Henrik, 1974-
(författare)
-
Activity-Based Costing : avbildning, integration & nytta
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This doctoral dissertation provides an extensive analysis of Activity-Based Costing, one of the most discussed management accounting models during the 90's. The aim of the study is to analyse the prerequisites for the design, integration and use of Activity-Based Costing systems. Three perspectives are used in the analysis:Correspondente perspective - referring to the ability of integrated ABC-systems to depict the reality they intend to describe.Integration perspective - referring to the possibilities of integrating ABC-systems with other systems in an organisation.Usefulness perspective - referring to the user needs for activity-based information, the value/usefulness of activity-based information and the method's effects on user behaviour.The results of the dissertation show that an effective ABC-system has a low degree of sophistication, allocation and integration. Yet such ABC-systems have a higher information value compared to more complex systems. These simple integrated ABC-systems also show positive volume and standardisation effects. This dissertation contributes with empirical descriptions of advanced integrated Activity-Based systems and models that are generated from each of the above mentioned analytical perspectives. Moreover, the dissertation's synthesis is presented as a three dimensional model showing the effective ABC-system. Finally, a two-piece model is suggested as a possible solution to the problems associated with the ABC-model.
|
|
| 3. |
- Nilsson, Göran, 1963-
(författare)
-
Processorientering och styrning : regler, mål eller värderingar?
- 2003
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Frågan är om det under de senaste femton åren funnits något mer populärt managementkoncept än processorientering. När en organsation genomför en förändring som införande av processorientering kan detta givetvis påverka ett antal olika aspekter i organisationen. Frågan som belyses i denna avhandling är vad som händer med styrningen vid förändringar mot ökad processorientering. Särskilt fokuseras vad som händer med betoningen av olika styrformer som regelstyrning, målstyrning och styrning med värderingar. För att belysa detta har två förändringsprocesser som syftat till ökad processorientering studerats, den ena i form av en aktionsforskningsstudie och den andra i form av en retrospektiv fallstudie. Dessa två fall illustrerar en stor spridning i processorienteringsansatserna. Den ena ansatsen som benämns mekanistisk uppvisar stora likheter med taylorism och fordism. Den andra som benämns organisk uppvisar snarare likheter med socioteknik och cultural management. Hur styrningen förändras i fallen visar sig vara kopplat till vilken processorienteringsansats som tillämpas. Trots olikheterna i ansatserna är syftena med processorientering likartade i de två fallen. Studien visar dock att den organiska ansatsen kopplar starkare till syftena än den mekanistiska. För att analysera varför respektive processorienteringsansats kommit att tillämpas och varför styrningen förändrats i olika riktningar har contingencyteori, institutionell och kognitiv organisationsteori använts.
|
|
| 4. |
- Persson, Lars Åke, 1947-
(författare)
-
Nutrition and health in infancy and childhood : an epidemiological approach to the assessment of dietary habits, their determinants and implications
- 1984
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to describe the distribution of feeding habits and dietary habits of Swedish children of different ages, to search for determinants of the observed distributions and to analyse some possible implications of those habits regarding health and growth. The present results emanate from a longitudinal study of feeding, growth and development of 312 infants and from a cross-sectional study on the dietary habits of 738 children aged 4,8 and 13 years.The dietary assessement techniques used in these epidemiological studies are evaluated (e.g. 24-hour recall, 7-day recording of food intake and dietary history technique).The infant feeding habits in three communities are described and the variation of those habits in different strata is discussed. Breastfeeding habits are analysed using multivariate techniques.The energy and nutrient intake of weaned infants aged 6 and 12 months was characterized by a good supply of most nutrients in comparison with recommended dietary allowances. The mean energy intake of the studied, normally-growing infants at 6 months was 80 per cent of the recommended intake.The growth velocity during the first three months of life for entirely breastfed infants was found to be higher than for mixed-fed or formula-fed infants. The need for a revision of present growth standards for use in breastfed populations during the first 6 months of life is discussed.An attempt was made to formulate a causal model for dental caries, including dietary factors and caries-preventive activities, and to make som quantitative interpretations from this model and the present set of data.Dietary habits associated with different short- or long-term health risks were analysed in the ages 4, 8 and 13 years. The dietary intake of iron was satisfactory and no cases of iron deficiency anaemia were found. On average 10 per cent of the daily energy intake derived from sucrose. The fat intake was characterized by a high intake of saturated fat and a low P/S ratio. Most children had a daily sodium intake above recommended levels. The prevalence of obesity differed between different social strata, especially in the oldest age group. Overweight children did not have a higher energy intake than normal-weight children. The need for a population approach to prevention in childhood of some diet-related health problems in adult life is discussed.The present dietary patterns and health of children in northern Sweden are compared with the situation 15 and 50 years ago, when nutrition surveys were performed in the same areas.
|
|
| 5. |
|
|
