| 1. |
- El Jamal, Sawsan
(author)
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Stability of Alternative Nuclear Fuel Materials in Aqueous Systems
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Nuclear power produces a large portion of the electricity worldwide. It has been the largest low-carbon energy source for more than 30 years and has played an essential role in the security of energy supplies for many countries. However, despite its advantages, its future is unknown mainly because of accidents that can happen under reactor operation and the high radioactivity of the fuel after use. Therefore, Generation IV nuclear power has been introduced as it promises a sustainable and economical way of producing energy and reduces some of the risks observed in current reactors. UC and UN have advantageous properties compared to conventional UO2-based fuel which makes them promising fuel candidates for Generation IV nuclear reactors. Even though the fuel for Generation IV reactors is planned to be reprocessed, unexpected political decisions may change these plans, and the used fuel could end up in a geological repository. Therefore, the behavior of these new fuel materials must be understood in accident scenarios in reactors as well as under deep geological repository conditions. The radioactivity of the used fuel will induce radiolysis of water that comes in contact with it. This will lead to oxidative dissolution of the fuel and this is one of the potential routes for radionuclide release in the environment.In the first part of this thesis, UC and UN have been investigated in aqueous solutions under anoxic conditions, and under the influence of external γ-radiation and H2O2, the latter mimicking the impact of α-radiolysis. The hydrolysis of these materials in aqueous systems resulted in matrix dissolution which is not observed for UO2. The oxidative dissolution induced by H2O2 is more prominent than hydrolysis in water with or without added HCO3- where higher concentrations of dissolved uranium can be detected. In addition, the differences in reactivity are discussed for these materials and H2O2 is most reactive towards UN followed by UC and finally UO2, yet the dissolution yield is the lowest for UN. The change in UC and UN behavior with consecutive exposure to H2O2 was attributed to a change in surface reactivity where catalytic decomposition of H2O2 becomes possible. As it was observed for H2O2 additions, radiation induced oxidative dissolution also dominates over hydrolysis. Unexpectedly high concentrations of H2O2 were observed in the irradiated systems. This was found to be due to formation of nano-particulate studtite that could not be separated from the solutions samples by filtration. Hence, it turned out to be impossible to determine the free U(VI) and H2O2 concentrations in these systems.Finally, the stability of pure and ZrN containing UN pellet fragments was investigated in aqueous system under external γ-radiation or H2O2 exposure. The behavior of these pellet fragments was similar to the UN powder where the dissolution of uranium was enhanced under oxidizing conditions if compared with anoxic conditions (hydrolysis). Consecutive exposures of UN pellet fragments to H2O2 showed a change in surface reactivity. This change is attributed to the formation of an oxide layer on the surface of UN, as UO2 is less reactive towards H2O2 and UO2 pellets display lower dissolution yields than UN pellets. In addition, the impact of ZrN as a stabilizing additive to UN pellets was studied. The addition of ZrN to UN is expected to stabilize the UN matrix and thus render a more accident tolerant fuel. Interestingly, it was shown that under oxidizing conditions, ZrN did not have a significant impact on the stability of UN pellets in aqueous systems
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| 2. |
- Johnsson, Linus, 1978-
(author)
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Trust in Biobank Research : Meaning and Moral Significance
- 2013
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Doctoral thesis (other academic/artistic)abstract
- What role should trust have in biobank research? Is it a scarce resource to be cultivated, or does its moral significance lie elsewhere? How does it relate to the researcher’s individual responsibility?In this thesis I draw four general conclusions. First, trust is still very much present in at least some biobanking settings, notably in Sweden, but possibly also internationally. Second, a morally relevant conception of trust entails that to be trustworthy, researchers must consider the normative expectations that people have of them, and renegotiate expectations that are mistaken. Third, this conception differs from “public trust” assessed through surveys. The main use of the latter is to legitimate policy, not to identify moral duties. Fourth, in spite of ethics review, guidelines and informed consent procedures, ethical issues will always arise during the course of a research project. Researchers can therefore never avoid their individual moral responsibility. Ensuring that one is adequately trusted is one step towards conducting morally acceptable research.Study I indicates that few Swedes refuse storage of samples in healthcare-associated biobanks and their use in research. Study II suggests that people are somewhat more willing to donate samples than surveys indicate, especially when approached face-to-face by health care personnel. Relationships of trust might thus be important in people’s decision-making. Study III investigates trust as a moral concept. The trustee is often in a unique position to determine what the other’s trust amounts to. When it is mistaken, the trustee has an obligation to counteract it, compensate for it, or renegotiate the expectations that cannot be met. In Study IV, I critique the feasibility of guaranteeing the trustworthiness of the research apparatus through formal measures such as ethics review and guidelines. Not only are there limitations of such measures to consider. They also risk blinding researchers to ethical issues that are not covered by the rules, fostering moral complacency, and alienating researchers to ethics.
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| 3. |
- Terekhina, Irina, 1994-
(author)
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On selective glycerol valorisation : Exploring the performance of facet-controlled nanoelectrocatalysts
- 2024
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Doctoral thesis (other academic/artistic)abstract
- As the biodiesel industry's growth skyrocketed in the past 20 years, it resulted in the accumulation of its main by-product—glycerol. Despite its extensive applications in the pharmaceutical industry, medicine, cosmetics, agriculture, and food industries, the supply exceeds the demand. Hence, glycerol, being abundant and cheap, has emerged as a promising feedstock for producing value-added chemicals. One of the tactics to generate those products is the glycerol electrooxidation reaction (GEOR), where glycerol is oxidised at the anode and hydrogen gas is generated at the cathode.In the present thesis, noble metal-based nanoparticles were synthesised, characterised, and evaluated in alkaline media as catalysts for the GEOR. In order to assess and optimise the electrocatalytic performance and selectivity of the GEOR toward three-carbon (C3) products, different parameters like the morphology and composition of the catalyst, exposed crystallographic facets, electrolyte composition and electrolysis potential were studied.The centre of the attention of the research covered were Pd, Pd-Ni, Pt and Pt-Co nanoparticles with an octahedral, rhombic dodecahedral, and cubic shape and more irregular shapes. Cubic-shaped catalysts with {100} faces were the best-performing among the investigated systems. In addition, alloying of Pd and Pt with non-noble Ni and Co improved the efficiency of the GEOR compared to their noble monometallic counterparts while generally retaining the selectivity of C3 products mostly represented by glycerate and lactate.
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| 4. |
- Shafeie, Samrand, 1984-
(author)
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Structure and Properties Investigations of the La2Co1+z(Ti1-xMgx)1-zO6 Perovskite System
- 2011
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Licentiate thesis (other academic/artistic)abstract
- Perovskite based materials have great potentials for various energy applications and the search for new materials for uses in SOFCs has largely been concentrated to this class of compounds. In this search, we have studied perovskite phases in the system La2Co1+z(Ti1-xMgx)1-zO6, with 0 x 0.9 and z = 0.0, 0.2, 0.4, 0.6. Crystal structures were characterized by XRD and, for selected compositions, also by NPD and SAED. They exhibit with increasing x, as well as increasing z, a progressive increase in symmetry from monoclinic to orthorhombic to rhombohedral. The main focus in this work has been on the investigation of structure-property relations for compositions with 0.0 x 0.5 and z = 0. The nominal oxidation state of Co increases for these with increasing x, from Co2+ for x = 0 to Co3+ for x = 0.5. Magnetic measurements and XANES studies showed that the average spin state of Co changes linearly with increasing x, up to x = 0.5, in accordance with varying proportions of Co with two fixed oxidation states, i.e. Co2+ and Co3+. The data suggests that the Co3+ ions have an IS spin state or a mixture of LS and HS spin states for all compositions with nominally only Co2+ and Co3+ ions, possibly with the exception of the composition with x = 0.1, 0.2 and z = 0, for which the data indicate that the spin state might be HS. The XANES data indicate furthermore that for the perovskite phases with z = 0 and x > 0.5, which in the absence of O atom vacancies contain formally Co4+, the highest oxidation state of Co is Co3+, implying that the substitution of Ti4+ by Mg2+ for x ³ 0.5 effects an oxidation of O2- ions rather than an oxidation of Co3+ ions. The thermal expansion was found to increase nearly linearly with increasing oxidation state of Co. This agrees well with findings in previous studies and is attributable to an increase in the ionic radius of Co3+ ions with increasing temperature, due to a thermal excitation from a LS to IS or LS/HS spin states. High temperature electronic conductivity measurements indicate that the electronic conductivity increases with an increase of both relative and absolute amount of Co3+. The latter can be attributed to an increase in the number of Co-O-Co connections. Additional high temperature magnetic measurements for selected samples, whose susceptibilities did not follow a Curie law behaviour up to room temperature, showed effective magnetic moments that did approach plateaus even at high temperatures (900 K). Interpretations of these data are, however, hindered by the samples losing oxygen during the applied heating-cooling cycle. The present study has shown that the investigated system is suitable for further studies, of more fundamental character, which could provide further insight of the structure-property relationships that depend on the oxidation state of Co.
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| 5. |
- Urbonaite, Sigita, 1974-
(author)
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Synthesis and Characterisation of Carbide Derived Carbons
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Carbide derived carbons (CDCs) have been synthesised through chlorination of VC, TiC, WC, TaC, NbC, HfC and ZrC at different temperatures. The aim of the investigation was to systematically study changes of structural and adsorption properties depending on the synthesis conditions. CDCs were characterised using nitrogen and carbon dioxide adsorption, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and electron energy loss spectroscopy. The studies revealed the CDCs structures to range from amorphous to ordered, from microporous to mesoporous. It was found that structural ordering and porosity can be modified by: i) synthesis temperature, ii) precursor, iii) density and volume of precursor, iv) catalysts, v) incorporation of nitrogen in to carbide structure, and CDCs can be tuned up to the demanded quality. They also exhibited a high potential for methane storage.
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| 6. |
- Ahmed, Taha, 1984-
(author)
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Nanostructured ZnO and metal chalcogenide films for solar photocatalysis
- 2023
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Doctoral thesis (other academic/artistic)abstract
- The increasing demand for clean energy and safe water resources has driven the development of efficient and sustainable technologies. Among these technologies, photocatalysis using semiconducting materials has emerged as a promising solution for both solar hydrogen generation and water purification. Low-dimensional ZnO, including nanorods, nanoparticles, and quantum confined particles (so called quantum dots), has demonstrated excellent photocatalytic properties due to their large surface area, high electron mobility, and tunable band gap.The work in this thesis aims to investigate the potential of low-dimensional ZnO alone and in combination with CdS and Fe2O3 for solar hydrogen generation and photocatalytic water purification. The thesis includes a comprehensive analysis of the synthesis, characterization, and optimization of low-dimensional ZnO-based photocatalyst systems for solar hydrogen generation and photocatalytic water purification. Additionally, the thesis will evaluate the performance of the ZnO-based photocatalysts under different experimental conditions, either as photoelectrodes or as distributed particle systems for water purification. The work includes detailed size control of ZnO by itself in dimensions below 10 nm using a hydrothermal method, to provide an increased total surface area and introduce quantum confinement effects that increase the band gap to enable degradation of chemical bonds in a model pollutant in a distributed system for water purification. The work also includes a relatively detailed study of the phonon–phonon and electron–phonon coupling as a function of dimension from 10 nm to 150 nm for ZnO using non-resonant and resonant Raman spectroscopy. Ultimately, the thesis aims to provide insight into the potential of low-dimensional ZnO alone and in combination with other inorganic materials for solar hydrogen generation and photocatalytic water purification and pave the way for the development of efficient and sustainable technologies for clean energy and safe water resources.
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| 7. |
- Anderberg, Mats, 1961-, et al.
(author)
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Strukturerade intervjuer inom missbruksvården : - som en grund för kunskapsutveckling
- 2009
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Doctoral thesis (other academic/artistic)abstract
- Anderberg, Mats & Dahlberg, Mikael (2009). Strukturerade intervjuer inom missbruksvården – som en grund för kunskapsutveckling (Structured interviews in substance abuse treatment - as a foundation for the development of knowledge). In the discussion on knowledge development in social work, structured interviews have attracted an increasing amount of attention. The aim of this thesis is to examine and analyze how structured interviews can serve as a basis in the compilation and development of knowledge for practice and research in addiction treatment. More precisely, it means a problematization of the methodological issues that are of central importance in studying treatment outcomes, in which structured interviews form the basis. The methodological aspects in focus here are scientific concepts such as reliability, validity and specific factors in the evaluation of treatment interventions. A further objective is to outline a model for analysis when compiling and evaluating treatment outcome. The five empirical studies have been conducted in their natural context, in organisations in which structured interviews with clients are carried out as an everyday routine and used for e.g. treatment planning. The structured interview DOK (a Swedish abbreviation for Documentation of clients) is used as a basis and an example for the empirical studies in this thesis. The validation studies show that the DOK interview generally attains a good level of reliability and validity, but also contains a small number of variables that do not live up to the requirements which may be imposed. Deficiencies in operationalization and question construction seem to have a large impact. Another conclusion is that it is possible to carry out validation studies, where each variable is examined separately and evaluated with the aid of both sound methodological starting points and relevant statistical theory. Another of the central questions, the thesis addresses, is how structured interviews can be used as a basis for evaluation of treatment. The two studies which highlight this issue show that it is obvious that structured interviews are suitable for such a purpose, through its standardized form and multi-dimensional nature. Validation of structured interviews or evaluation of social interventions should not be reduced to single numbers or values. The multidimensional nature of the structured interview shall also be reflected in the results and analysis. The thesis presents an analysis model for evaluating treatment outcome in relation to two empirical examples and foregoing theoretical starting points. Our view is that structured interviews can provide a link between practice and research and thus contribute to the development of knowledge in social work and substance abuse treatment.
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| 8. |
- Carlsson, Mats, 1970-
(author)
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Preparation and characterisation of refractory whiskers and selected alumina composites
- 2004
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Doctoral thesis (other academic/artistic)abstract
- A whisker is a common name of single crystalline inorganic fibre of small dimensions, typically 0.5-1 μm in diameter and 20-50 μm in length. Whiskers are mainly used as reinforcement of ceramics. This work describes the synthesis and characterisation of new whisker types. Ti0.33Ta0.33Nb0.33CxN1-x, TiB2, B4C, and LaxCe1-xB6 have been prepared by carbothermal vapour–liquid–solid (CTR-VLS) growth mechanisms in the temperature range 900-1800°C, in argon or nitrogen. Generally, carbon and different suitable oxides were used as whisker precursors. The oxides reacted via a carbothermal reduction process. A halogenide salt was added to form gaseous metal halogenides or oxohalogenides and small amount of a transition metal was added to catalyse the whisker growth. In this mechanism, the whisker constituents are dissolved into the catalyst, in liquid phase, which becomes supersaturated. Then a whisker could nucleate and grow out under continuous feed of constituents. The syntheses of TiC, TiB2, and B4C were followed at ordinary synthesis conditions by means of mass spectrometry (MS), thermogravimetry (TG), differential thermal analysis (DTA) and quenching. The main reaction starting temperatures and reaction time for the different mixtures was revealed, and it was found that the temperature inside the crucible during the reactions was up to 100°C below the furnace set-point, due to endothermic nature of the reactions. Quench experiments showed that whiskers were formed already when reaching the temperature plateau, but the yield increased fast with the holding time and reached a maximum after about 20-30 minutes. Growth models for whisker formation have been proposed.Alumina based composites reinforced by (2-5 vol.%) TiCnano and TiNnano and 25 vol.% of carbide, and boride phases (whiskers and particulates of TiC, TiN, TaC, NbC, (Ti,Ta)C, (Ti,Ta,Nb)C, SiC, TiB2 and B4C) have been prepared by a developed aqueous colloidal processing route followed by hot pressing for 90 min at 1700°C, 28 MPa or SPS sintering for 5 minutes at 1200-1600°C and 75 MPa. Vickers indentation measurements showed that the lowest possible sintering temperature is to prefer from mechanical properties point of view. In the TiNnano composites the fracture mode was typically intergranular, while it was transgranular in the SiCnano composites. The whisker and particulate composites have been compared in terms of e.g. microstructure and mechanical properties. Generally, additions of whiskers yielded higher fracture toughness compared to particulates. Composites of commercially available SiC whiskers showed best mechanical properties with a low spread but all the other whisker phases, especially TiB2, exhibited a great potential as reinforcement materials.
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| 9. |
- Hu, Shichao, 1986-
(author)
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Transition metal oxofluorides comprising lone pair elements : Synthesis and Characterization
- 2014
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Doctoral thesis (other academic/artistic)abstract
- Within the family of transition metal oxochlorides/bromides containing lone pair elements, the transition metal cations often adopt a low-dimensional arrangement such as 2D layers, 1D chains or 0D clusters. The reduced dimensionality is attributed to the presence of stereochemically active lone pairs which are positioned in the non-bonding orbital and will not participate in bond formation and instead act as structural spacers that help to separate coordination polyhedra around transition metal cations from forming three dimensional networks. On the other hand, the chlorine and bromine ions also play an important role to open up the crystal structure because of their low coordination number. However, fluorine has been rarely used in this concept due to the difficulties in synthesis.This thesis is focused on finding new compounds in the M-L-O-F system (M = transition metal cation, L= p-block lone pair elements such as Te4+, Se4+, or Sb3+) in order to study the structural character of fluorine. Hydrothermal reactions have been adopted instead of conventional chemical transport reactions that are commonly used for synthesizing compounds in the M-L-O-(Cl, Br) family. A total of 8 new transition metal oxofluorides containing lone pair elements have been synthesized and their structures have been determined via single crystal X-ray diffraction. Bond valence sum calculations are used to distinguish in between fluorine and oxygen due to their very similar X-ray scattering factors.
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| 10. |
- Johnsson, Andreas, 1977-
(author)
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Modeling, Implementation and Evaluation of IP Network Bandwidth Measurement Methods
- 2007
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Doctoral thesis (other academic/artistic)abstract
- Internet has gained much popularity among the public since the mid 1990's and is now an integrated part of our society. A large range of high-speedbroadband providers and the development of new and more efficient Internet applications increase the possibilities to watch movies and live TV, use IP-telephony and share files over the Internet. Such applications demand high data transmission rates, which in turn consume network bandwidth. Since several users must share the common bandwidth capacity on the Internet, there will be locations in the network where the demand is higher than the capacity. This causes network congestion, which has negative impact on both the data transmission rate and transmission quality.This thesis is about methods for measuring the available bandwidth of a network path between two computers. The available bandwidth can be interpreted as the maximum transfer rate possible without causing congestion. By deploying the methods studied in this thesis the available bandwidth can be measured without previous knowledge of the network topology. When an estimate of the available bandwidth is obtained, the transfer rate when sending messages between computers can be set to the measured value in order to avoid congestion.In the thesis an active end-to-end available bandwidth measurement method called "Bandwidth Available in Real Time" (BART for short) is evaluated. BART measures the available bandwidth by injecting probe packets into the network at a given rate and then analysing how this rate has changed on the receiving side. A Kalman filter is used to update the current estimate of the available bandwidth using the new measurement sample.The focus of the thesis is on how methods, such as BART, function in wireless 802.11 networks, which are very popular in work as well as in home environments. Wireless networks have a different construction compared to many other types of networks and this can affect the accuracy of the measurement methods discussed in this thesis. The effects must be analyzed and understood in order to obtain accurate available bandwidth estimates. Since wireless links are often parts of the network path between a sender and a receiver on the Internet, it is important to study how these links affect the estimates of the available bandwidth.
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