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| 2. |
- Wojas, Natalia
(författare)
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The dynamic surface nature of calcite and its role in determining the adsorptive stability toward hydrophobizing carboxylic fatty acids
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Calcium carbonate has attracted a lot of interest over the centuries. Nowadays, mainly as mineral pigment and filler, it has a wide use in technological applications ranging from paper, construction, polymers, and environmental solutions to consumer goods. Amongst these uses, the filler pigment is required to display either hydrophilicity (for applications in aqueous colloidal systems, including, for example, in paper and emulsion paints), or, in contrast, oleophilicity (for applications in contact with oil-based systems, such as plastics and volatile solvent-containing sealants). To achieve oleophilicity, and resulting hydrophobicity, the filler is surface treated, typically using carboxylic fatty acids. In this thesis, effects of humidity and fatty carboxylic acids vapor on CaCO3 surface wettability and nanomechanical properties were studied, with the aim to gain knowledge on layer packing density and order, as well as resistance to water exposure and mechanical wear. A better understanding of the dynamic nature of the calcite surface presented in this work allows the industry to increase sustainable control over materials production and storage. First, a setup combining an atomic force microscope (AFM) with a humidifier was used to map nanomechanical properties of growing surface domains (hydrated form of CaCO3) formed by ion dissolution, diffusion, and redeposition, a process that is not reversible upon drying. Secondly, AFM and contact angle goniometer measurements showed that the stability of the calcite surface improves with increasing carboxylic acid chain length (C2 to C18). Meanwhile, X-ray photoelectron spectroscopy and vibrational sum frequency spectroscopy techniques demonstrated that a coherent layer with maximum packing density of carboxylate and carboxylic acid species was achieved with the use of stearic acid (C18) with high enough vapor pressure and exposure time. The AFM images successfully visualized that a complete C18 monolayer is capable of countering nano-wear of the calcite surface despite the humidity (under the range of loads investigated in this work) and the layer has self-healing properties, while calcite displayed high abrasive wear. Further, when calcite coated by a highly packed monolayer of C18 was covered with a water droplet, a large contact angle hysteresis resulted in a coffee ring effect (CRE). That is leading to formation of hillocks at the contact line consisting of dissolved fatty carboxylic acid and possibly calcium bicarbonate Ca(HCO3)2 molecules transported from the bare calcite region that also is created next to the droplet edge. Interestingly, C18 coated calcite remained considerably more stable in the case where a water droplet saturated with octanoic acid was used instead of water; thus, it was concluded that the CRE can be contained via reduction of the liquid surface tension and contact angle hysteresis.
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| 3. |
- Chen, Si, 1985
(författare)
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Miniaturized localized surface plasmon resonance biosensors
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Abstract Reliable and sensitive biosensors are required for fast and accurate diagnostics. Localized surface plasmon resonances (LSPRs) in noble-metal nanoparticles possess very high refractive index sensitivity close to the metal surface and therefore constitute an attractive biosensing platform. In this thesis, label-free biosensing with LSPR was investigated and demonstrated. The spatial sensing ranges of the particles were determined by thin layer deposition of dielectric materials. A comparison between the classical SPR and LSPR was performed using the same experimental setup. No obvious performance difference between the two sensing techniques was found. The versatility of the LSPR sensing technique was demonstrated by miniaturization of the sensor area, which could be reduced down to ~250 nanoparticles without compromising the short-term noise level. To further miniaturize the LSPR sensor, multiple single nanoparticles were measured using hyperspectral imaging. It was shown that by combining LSPR refractive index sensing and an enzyme linked immunoassay (ELISA), i.e. a horseradish peroxidase catalyzed precipitation, an extremely low surface coverage of enzyme molecules could be detected on single isolated nanoparticles. In a follow up investigation, electron beam lithography (EBL) and hyperspectral imaging were combined to enable simultaneous measurements of up to 700 individual particles. This made it possible to study statistical variations between the sensor particles. The observed variations in the responses from individual particles were interpreted as a result of large variations in sensitivity over the particle surface combined with the size distribution of the precipitate. In a separate study, a photo functionalization strategy compatible with LSPR biosensors was investigated. A biotin moiety was successfully functionalized with UV light on a self-assembled monolayer of photoactive nitroindoline on gold surfaces. Adsorption of streptavidin and streptavidin conjugated HRP to the surface-bound biotin could be monitored by the LSPR sensor. This strategy might be utilized for spatially localized surface functionalization for multiplexed miniaturized LSPR sensors. In summary, despite many experimental problems, the results discussed in this thesis point towards a number of important biosensing applications of plasmonic nanoparticles.
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| 4. |
- Görnerup, Olof, 1977
(författare)
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Inference of Hierarchical Structure in Complex Systems
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hierarchical organization is a central property of complex systems. It is even argued that a system is required to be hierarchical in order to evolve complexity within reasonable time. A hierarchy of a system is defined as the set of self-contained levels at which the system operates and can be described on. Given a dynamical system there are only specific levels that are valid. This thesis mainly concerns the definition and inference of such levels. Paper I describes an algorithm for finding hierarchical levels in stochastic processes. The method systematically explores the set of possible partitions of a process' state space and statistically determines which of the partitions that impose closed dynamics. It is applicable to moderately sized systems. In Paper II an alternative approach that applies to linear dynamical systems is presented. In this case the spectral properties of the matrix that defines a system's dynamics is utilized, which allows for analysis of large systems (with on the order of thousand states). The specification and analysis of an algorithm that is based on the results in Paper II is presented in Paper III. Paper IV applies the spectral method and a complementary agglomeration method to infer aggregated dynamics in a Markov model of codon substitutions in DNA. The standard genetic code is identified as a projection that gives the hierarchical level of amino acid substitutions. Further, higher order amino acid groups that are relatively conserved under substitutions are found to define other levels of dynamics. Paper V and VI relate hierarchical organization to primordial evolution in a conceptual model that is based on the RNA world hypothesis. A well-stirred system of processes that catalyze the production of other processes is shown to successively build higher levels of organization from simple and general-purpose components by autocatalysis.
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| 5. |
- Sundell, Gustav, 1985
(författare)
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Atomic Scale Degradation of Zirconium Alloys for Nuclear Applications
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to their low thermal neutron capture cross-section, zirconium alloys are widely used in the nuclear industry as fuel cladding and for structural components. The lifetime of the fuel assemblies in the reactors is primarily dictated by the ability of the cladding to withstand oxidation and hydrogen pick-up from the coolant water and radiation damage induced by the neutron flux.In order to study the hydrogenation and irradiation damage of zirconium on the atomic scale, atom probe tomography (APT) is utilized. This technique offers some unique virtues for nanometer scale materials analysis, such as equal sensitivity to all elements and near-atomic resolution. However, as APT has rarely been used for hydrogen studies previously, methods for accurate qualitative and quantitative analysis need to be developed. In this thesis, methods to control adsorption of hydrogen onto the APT specimen are explored. Techniques for hydrogen measurement are further developed using deuterium, whereby it is shown that hydrogen enters the alloy through grain boundaries in the oxide scale. A model for mitigation of hydrogen pick-up is proposed, in which oxide grain boundaries are decorated with transition metal alloying elements such as Fe and Ni, which affects the probability of reducing ingressing protons to form inert H2 gas.Zr alloys incur irradiation damage when subjected to the neutron flux in the reactor core, dissolving secondary phase particles and generating dislocation loops that embrittle the material. By studying the microstructure on the atomic scale before and after prolonged in-rector exposure, it is shown how the alloying elements in Zr interact with the irradiation-induced lattice defects.
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| 6. |
- van den Bossche, Maxime, 1989
(författare)
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Methane oxidation over palladium oxide. From electronic structure to catalytic conversion
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding how catalysts work down to the atomic level can provide ways to improve chemical processes on which our contemporary economy is heavily reliant. The oxidation of methane is one such example, which is important from an environmental point of view. Methane is a potent greenhouse gas and natural and biogas vehicles need efficient catalysts to prevent slip of uncombusted fuel into the exhaust. Commercial catalysts for methane oxidation are often based on palladium or platinum. Metallic palladium, however, is easily converted to palladium oxide when the engine is operated at oxygen rich conditions. In this thesis, various aspects of complete methane oxidation over PdO(101) are investigated with computational methods based on density functional theory (DFT). PdO(101) is the active surface for methane oxidation, and firstly, the reaction intermediates CO and H are studied in detail. Possible pathways for H2 adsorption, dissociation and eventual water formation are investigated, in connection to core-level spectroscopy experiments. Similarly, the adsorption configurations for carbon monoxide on clean and oxidized palladium are examined with a combination of DFT calculations, core-level and infrared spectroscopy. Secondly, a detailed kinetic model is constructed that describes the catalytic conversion of CH4 to CO2 and H2O over PdO(101). This is done in a first-principles microkinetics framework, where the kinetic parameters are obtained by applying density functional and transition state theory. The kinetic model provides a fundamental understanding of findings from reactor experiments, such as the rate limiting steps and poisoning behaviour, and shows qualitatively different behaviour of adsorbates on oxide as compared to metal surfaces. Lastly, limitations of the commonly used class of generalized gradient functionals are illustrated in the computation of several properties of adsorbates on metal oxide surfaces. These include core-level shifts and thermodynamic and reactive properties of adsorbates on the PdO(101) surface. Similarly, the description of several molecular and cooperative adsorption processes are also found to be sensitive to the applied exchange-correlation functional on the BaO(100), TiO2(110) and CeO2(111) surfaces.
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| 7. |
- Larsson, Johanna, 1986-
(författare)
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Trainee teacher identities in the discourses of physics teacher education : Going against the flow of university physics
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates what is involved in being recognized as a legitimate physics teacher-to-be in a Swedish physics teacher programme. Drawing on in-depth, qualitative interviews with 17 physics teacher educators and 17 trainee physics teachers, this thesis sees learning to become a physics teacher as a process of performing professional identities. It demonstrates aligning discourses of educators and trainees, and outlines a number of challenges that trainees have to negotiate when learning to become physics teachers.The first part of the project analyzes the discourses of teacher educators. Four discourse models are identified which demonstrate how the talk of physics lecturers portrays the default goal of learning physics as becoming a researcher. Choosing to become a teacher in this system, means diverting from the expected path of a physics student, and moving backwards towards school physics. In such a system, trainee physics teachers are described as less competent and ambitious than other physics students, and can be understood to be incomprehensibly “going against the flow” of university physics by aiming towards school physics.The second part of the project shows how physics courses are experienced by the trainee physics teachers as primarily meeting the needs of other student groups. The educators’ talk about trainee teachers as less competent and ambitious is mirrored by trainees who see no incentive to try hard for good results. The analysis shows a physics study culture that emphasises brilliance and nerdiness, resulting in a passive classroom culture and high stress. Deepened analysis of the identity negotiations of three female interviewees shows how trainee teachers are resourceful in navigating this study culture. Combining positions of feminine woman, trainee teacher, and physics student, these students create practices of relaxed and constructive physics learning that challenge the elitist physics discourse.The education of physics teachers is important for many reasons. There are projected shortages of trained teachers, and physics teachers have the power to affect how physics, a field that is lacking diversity, is perceived by young people. By exploring how becoming a physics teacher is entangled with discourses of competence, femininity, and the status of the physics discipline this thesis takes a novel approach to the education of physics teachers. The findings suggest that physics faculty in their role as teacher educators examine assumptions about physics teacher education and trainee physics teachers, and can be used to empower trainee physics teachers to challenge norms of brilliance and masculinity in physics.
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| 8. |
- Pendrill, Florence, 1983
(författare)
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Where have all the forests gone? Quantifying pantropical deforestation drivers
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Deforestation across the tropics continues to be a major source of greenhouse gas emissions and the largest threat to biodiversity on land. With strengthened commitments to reduce deforestation from countries and companies alike, it is crucial that renewed investments for reducing deforestation be guided by a sound understanding of what drives deforestation. This thesis gives a comprehensive picture of the amount of deforestation and concomitant carbon emissions driven by the expansion of agricultural commodities across the tropics and its link to international trade. The included papers show that pasture and a handful of crops drive a large share of the deforestation resulting in the expansion of productive agriculture. The main demand for these commodities is domestic consumption; even so, imports of food commodities associated with deforestation can still constitute a large part of the consumer countries’ carbon emissions due to consumption (e.g., in the EU). This thesis contributes empirical evidence relating to forest transition theories by showing that many countries with increasing forest cover tend to import products associated with deforestation elsewhere, thereby offsetting around one-third of their forest gains. The thesis also introduces a conceptual distinction between two categories of agriculture-driven deforestation, based on whether it results in productive agricultural land or not. Though almost all deforestation is agriculture-driven, one-third to one-half of agriculture-driven deforestation occurs without the expansion of productive agricultural land. Instead, it may be due to several potential mechanisms, such as land speculation, tenure issues, or fires. Put together, these results indicate that it is crucial that policies to curb deforestation go beyond focusing only on trade in specific commodities, to help foster concerted action on rural development, territorial governance, and land-use planning. This thesis also highlights key evidence gaps on the links between deforestation and agriculture: (i) the attribution of deforestation to specific commodities currently often relies on coarse or outdated data, (ii) there is a need for improved data on deforestation trends, and (iii) our understanding of deforestation drivers is systematically poorer for dry forests and Africa.
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| 9. |
- Dall` Olio, Daria, 1981
(författare)
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Magnetic fields around massive protostars as traced by masers and dust emission
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is not fully clear how the magnetic field acts during the first stages of star formation. A possible way to clarify its role is to observe the polarized light coming from masers and thermal dust emission. By measuring linear polarization angles and Zeeman splitting of different maser species it is possible to study the magnetic field morphology and strength in different parts of the protostar. Polarized emission of thermal dust has also been used extensively to probe the magnetic field at the onset of star formation. In this thesis we study the magnetic field properties of two well-known sources: the massive protostar IRAS18089-1732, showing a hot core chem- istry and a disc-outflow system, and the high-mass star forming complex G9.62+0.19, presenting several cores at different evolutionary stages. We also investigate the polarization properties of selected methanol masers, con- sidering newly-calculated methanol g-factors and hyperfine components. We compare our results with previous maser observations and we evaluate the contribution of preferred hyperfine pumping and non-Zeeman effects. We make use of MERLIN and ALMA observations and we analyse the polarized emission by 6.7 GHz methanol masers and thermal dust. Simulations were run using the radiative transfer code CHAMP for different magnetic field values, hyperfine components and pumping efficiencies. We observe that the large scale field probed by dust continuum emission is consistent with the small scale magnetic field probed by masers. Moreover, in the G9.62+0.19 complex we resolved several cores showing polarized emission. We propose an evolutionary sequence of magnetic field in this complex, where the less evolved stellar embryo exhibits a magnetic field stronger than the more evolved one. From our simulations, we find that preferred hyperfine pumping can explain some high levels of linear and circular polarization. We also notice that non-Zeeman effects need to be considered in magnetic field studies. In conclusion, our work indicates that there is a link between the magnetic field at different scales. More masers observations will help in evaluating the relevance of non-Zeeman effects and obtain good estimates of magnetic fields close to the protostar. Future multi-wavelength and multi-scale observations, aimed at detecting polarized light from masers, thermal dust and thermal molecular lines, will help to constrain magnetic field properties around massive protostars.
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| 10. |
- Reymer, Anna, 1983
(författare)
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Unveiling Mechanistic Details of Macromolecular Interactions: Structural Design and Molecular Modelling of DNA-Protein Systems in Their Active State
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Molecular structure is fundamental for understanding mechanisms of molecular interactions. This applies not least to understanding biological function: every biological cell, whether bacterial or human, is an immensely complex system of thousands of molecules that exist in constant motion and interaction with each other. Structural properties of the two main classes of biological macromolecules, nucleic acids and proteins, have been studied in this Thesis focusing on functional interactions of both DNA and the DNA-binding enzyme human recombinase Rad51. DNA is a highly polymorphic molecule and its plasticity may be important for its function. Conformational mechanics of the DNA helix was addressed to understand interactions with dumbbell-shaped ruthenium(II) polypyridyl compounds, known for their remarkable ability to slowly thread one of their bulky centres through a tightly packed DNA stack, probably invoking large transient conformational rearrangements of the helix. Thread-intercalation rate is accelerated by several orders of magnitude if the DNA target sequence is a stretch of at least ten base pairs of AT, as well as by the hydrophobicity of the auxiliary “dumbbell” ligands: counterintuitively, a smaller and less hydrophobic compound takes longer times to thread. It is hypothesized that thread-intercalation might be facilitated by an A-like DNA conformation, induced by the outside binding of the Ru(II) compounds. An NMR study, aiming to solve a thread-intercalated structure of the binuclear Ru(II)-DNA complex, resulted in a groove-binding geometry, probably representing an initial binding mode preceding intercalation, a result emphasizing the elusiveness and immense complexity of the threading process. Turning back to simpler monomeric propeller-shaped Ru(II) compounds it was deduced that, despite acting as classic intercalators, they can “read out” the chirality of the DNA helix by enantiospecifically kinking it, in a fashion analogous to several families of operatory DNA binding proteins.Another operatory protein, human recombinase Rad51, that facilitates homologous recombination, the process of exchanging near identical-sequence DNA strands, is also mechanically acting on DNA, by stretching it. A 3-D high-resolution model structure of human Rad51 filament was solved by a combination of polarized-light spectroscopic data and molecular modelling. Highlighted by the model some interesting structural features could be addressed: strategic locations of two putative DNA binding loops inside the protein filament; as well as location of a putative ATP binding site at the interface between two protein subunits and in direct proximity to a supposed location of DNA – could hint about DNA docking mechanism and potential role of ATP in the protein function.The Rad51-DNA model has proven itself useful also in a follow-up study on the stimulatory role of Ca2+ in the strand exchange reaction by human Rad51. A mechanism is proposed involving a high affinity DNA binding state of the Rad51 filament induced by Ca2+, regulatorily crucial for the search of homology and subsequent DNA strands exchange.
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