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- Agić, Heda, 1989-
(författare)
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Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of the most important events in the history of life is the evolution of the complex, eukaryotic cell. The eukaryotes are complex organisms with membrane-bound intracellular structures, and they include a variety of both single-celled and multicellular organisms: plants, animals, fungi and various protists. The evolutionary origin of this group may be studied by direct evidence of past life: fossils. The oldest traces of eukaryotes have appeared by 2.4 billion years ago (Ga), and have additionally diversified in the period around 1.8 Ga. The Mesoproterozoic Era (1.6-1 Ga) is characterised by the first evidence of the appearance complex unicellular microfossils, as well as innovative morphologies, and the evolution of sexual reproduction and multicellularity. For a better understanding of the early eukaryotic evolution and diversification patterns, a part of this thesis has focused on the microfossil records from various time periods and geographic locations. Examination of microfossil morphology, cell wall microstructure and biochemical properties, reflect their intracellular complexity and function, and allow reconstructions of their life cycle, as well as observing the evolutionary pattern of change from Mesoproterozoic, to Cambrian-Ordovician transition. Several case studies included assemblages deriving from Mesoproterozoic, Neoproterozoic and early Paleozoic time intervals that show disparate morphotypes and innovative features indicative of algal clades. The Mesoproterozoic Ruyang Group in northern China has yielded a diverse microfossil assemblage that provides important clues about the diversification of different eukaryotic groups. Furthermore these microfossils contributed an additional evidence for the emergence of the crown group Eukarya by 1.7-1.4 Ga. In another part of this thesis, examination of wall microstructure and chemical properties via Raman spectroscopy has been used to assess the biological affinities of various Neoproterozoic problematic carbonaceous compression fossils. Studies on the early Phanerozoic (c. 545-485 Ma) assemblages from Estonia reconstructed patterns of the early radiations of phytoplankton and its evolutionary innovations. A continuing theme in this thesis has been using a combination of evidence of microfossils’ fine-scale morphology, ecology and chemical properties to determine their function in life, in addition to their systematic position.
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- Alvarez, Manuel, 1980-
(författare)
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Distribution Network Planning Considering Capacity Mechanisms and Flexibility
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing penetration of distributed energy resources (DERs) has posed challenges to the distribution system operator (DSO) from the operation and regulatory point of view. High penetration of DERs could have negative impacts on the performance of the distribution grid, and depending on the regulatory framework, the DSO's remuneration as well. In liberalized electrical systems, the focus on promoting eciency has led to the implementation of an incentive-based regulation that exerts additional pressure on the DSOs to reduce costs. Additionally, the European Parliament Directive 2009/72/EC establishes a regulatory unbundling among the distribution, production, and retailing activities within the same vertically integrated electric utility.A way of helping the DSO to cope with the posed challenges is by providing it with exibility. This exibility can be acquired from the planning stage, and later be used during the system operation. This exibility can stem from the DSO's ability to exert control on the demand and the supply side to balance the system and correct its operational state.Based on the European DSOs' current situation at facing the increasing penetration of DERs, this thesis investigates in non-wired exible grid tools to solve the distribution network expansion problem. The investigation focuses on exibility providers, in particular on energy storage systems and hydropower, and also on capacity mechanisms to translate the capacity from DERs into the grid's capacity for planning purposes.Given that the share of renewable sources among the DERs is increasing, and considering the importance of energy storage systems in providing exibility to balance renewable energy production, the eort has been turned on to developing a hydropower model and a generic storage model that t both planning and operational studies.Given the need for gearing the DERs' behavior into the DSO's decision making process during the planning and operational timescales, the design and implementation of a distribution capacity mechanism have been developed. The design of the capacity mechanism has been conceived considering its integration within the distribution network expansion problem.The outcomes of this thesis can be synthesized as follows: 1) A generic hydraulic/storage model provided with an equivalent marginal cost that aids in considering the impact of present decisions in the future costs. 2) A market oriented distribution capacity mechanism that gears DERs and the DSOs to benefit mutually. 3) A distribution network expansion planning formulation that integrates the capacity resource from DERs through the distribution capacity mechanism.
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- Andersson, Bea Angelica, 1992-
(författare)
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Finding fitness : empirical and theoretical explorations of inferring fitness effects from population-level SNP data
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The distribution of fitness effects (DFE) describes the likelihood that a new mutation has a specific effect on the fitness of an individual in a given population. The shape of the DFE is a result of several factors such as population size, mating system and selective environment, and can in turn influence the evolutionary potential of a species. The DFE has long been a field of intense research, but particularly since molecular methods enabled us to study of genetic variation in organisms empirically. This research has led to the development of several statistical methods that use population-level frequencies of single nucleotide polymorphisms (SNPs) to infer the DFE. However, these methods rely on assumptions about the data and the organism itself, which could potentially affect the accuracy of the inferences. In this thesis, I describe how two major factors – data quality and inbreeding – can affect the accuracy of DFE inferences. I also show how and when to (and when not to) use DFE inference methods based on SNP frequencies.All genomic datasets contain inaccuracies and some level of uncertainty. The data sets are therefore often treated to remove the gaps or less reliable information, such as genotypes with low coverage. Some data sets need heavy filtering, which could reduce the amount of data available for analysis. We show that the choice of filter method affects the size of the final data set and the accuracy of the estimated DFE.Many DFE estimation software assumes random mating within the study population. Unfortunately, this assumption induces some error when trying to estimate the DFE in inbred or selfing species. Some have assumed that this is a result of high rates of homozygosity in the data, and should only be a problem in populations with very high rates of selfing (>99%). We show that accuracy of the estimated DFE decreases already at relatively low rates of selfing (70%) and that removing homozygosity does not improve the accuracy, implying that another mechanism could be causing the error.
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- Andersson, Nils-Eric, et al.
(författare)
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The influence of hot rolling on the variation of through thickness structure of AA7010 thick plates
- 1997
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Ingår i: Thermo-Mechanical Processing in Theory, Modelling & Practice. - Stockholm : Svenska fören. för materialteknik. - 9163054213 ; , s. 284-289
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The variation of through thickness structure and yield strength of AA7010-T7451 thick plate has been investigated. Grain size at different depths were determined qualitatively by using optical microscopy. Texture measurements were carried out using x-ray technique at the same depths as grain size studies. Tensile property tests have been performed and the EBSP technique has been used to compare the degree of recovered and recrystallized grain structure at different depths. Tensile testing determined through thickness variations in yield. The expected W shape of longitudinal yield strength through thickness was not observed. The yield strength decreases towards the center of the plate. An increasing amount of big recrystallized grains (through the thickness from T/8 towards the center of the plate) appears to be the reason behind the decreasing through thickness yield strength.
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- Andersson, Nils-Eric, et al.
(författare)
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The influence of hot rolling on the variation of through thickness structure of AA7010 thick plates
- 1996
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Ingår i: Thermomechanical processing in theory, modelling and practice [TMP]2. - 9163054213 ; , s. 284-289
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The variation of through thickness structure and yield strength of AA7010-T7451 thick plate has been investigated. Grain sizes at different depths were determined qualitatively by using optical microscopy. Texture measurements were carried out using X-ray technique at the same depths as grain size studies and tensile property tests have been performed. EBSP techdque has been used to compare the degree of recovered and recrystallized grain structure at different depths. Tensile testing determined through thickness variations in yield strength. The well known W shape of longitudinal yield strength variation through the thickness was not observed. The influence of texture on the yield strength measured is discussed.
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