Matemaattis-luonnontieteellinen tiedekunta
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(Helsingin yliopisto, 2017)The aim of this work was to study the climate change impact on two specific abiotic risks affecting forests in Finland: fires and heavy snow loads. Approximately 1000 forest fires occur annually in Finland, but thanks to effective fire suppression, the average size of fires is only about 0.5 ha. Occasionally, heavy snow loading causes forest damage, which reduces stand quality in boreal forests experiencing cold winters. In Finnish forests, snow damage occurs most commonly in the eastern and northern parts of the country. The basic tools used in this work to evaluate the climate change impact were climate models. In addition, observational weather data and fire statistics were used. In evaluating the forest fire risk, the Canadian Fire Weather Index (FWI) system was used. Snow load amounts were estimated mainly by applying a snow load model developed at the Finnish Meteorological Institute (FMI). The results indicate that forest fire risk will most likely increase in the future due to increasing temperature and enhanced evaporation. However, there is large uncertainty regarding the rate of change, which originates from the differences between climate model responses to the same radiative forcing. Moreover, an increase in forest fire risk will at the same time increase the risk of conflagrations. Crown snow loads were projected to become heavier in northern Finland and in the regions of Kainuu and North Karelia next to the Russian border. In southern and western Finland the risk of snow damage is expected to decrease. The largest decrease in the risk is projected to occur in coastal areas. In the areas expected to experience increased risk of snow damage, conditions favouring both heavy wet snow loading and rime accretion were predicted to become more common. The results of this work can be utilized when considering climatically-driven risks in forest management.
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(Helsingin yliopisto, 2017)Electrical impedance tomography (EIT) is a rather new approach to medical imaging that is motivated by using electricity to determine the inside of a body. The clear advantage lies in the usage of harmless electric currents, in contrast to the ionizing radiation of X-rays, whereas the mathematical problem is inherently more challenging. In EIT we seek to reconstruct an image of the inner organs by determining their conductivity, i.e. how well electricity is conducted. As a medical imaging modality it is most promising in pulmonary and cardiac imaging, due to considerably different conductivity values in the air filled lungs (low conductive) and the blood filled heart (high conductive). EIT is in principle capable of monitoring the respiratory process, detecting pathologies in the lungs, and monitoring the heart activity. The main focus of this work is on the partial-boundary problem in EIT, that means one has only access to a certain part of the boundary and data can only be collected there. In a hospital setting these situations can arise when monitoring a critical or unconscious patient and hence one can only access the front of the torso (ventral position). Furthermore, practical complications can arise due to faulty, dislocated, or dispatched electrodes and hence leading to incomplete data. The methods presented in this thesis are capable of dealing with such incomplete data. Following the tradition of mathematical research we are also interested in quantifying the error incomplete data introduces to the reconstruction. In a short summary, this thesis investigates how to improve EIT reconstructions from partial-boundary data by utilizing concepts from an ideal mathematical setting as well as how to apply these methods to real electrode models and measurement data.
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(VTT, 2017)Currently, the preferred option for the long-term disposal of spent nuclear fuel (SNF) and potentially for future thorium-based fuels in Finland and Sweden is disposal in a geological repository. In deep bedrock, the release of Th, U and other radionuclides through man-made barriers and the geo- and biosphere will be controlled by the dissolution of the fuel by groundwater. Thorium dioxide is isostructural to uranium dioxide, sharing the same fluorite structure (space group Fm3m) and making it a useful analogue material for nuclear fuel, which mainly consists of UO2 (>95%). This thesis aimed to investigate the dissolution of ThO2, which was synthesised to approximate as closely as possible the microstructure of UO2 in a nuclear fuel matrix. The investigation consists of dissolution studies conducted using pellets, fragments (2 to 4 mm) and particles (80 to 160 µm) of 232ThO2. The evolution of dissolving surfaces and grain boundaries were examined by combining different microscope imaging techniques (scanning electron microscopy (SEM), atomic force microscopy (AFM), SEM with electron backscattering diffraction detector (SEM-EBSD) and profilometer imaging). Part of the dissolution experiments were conducted in the presence of a 229Th tracer to gain additional data on the dissolution and precipitation by following the change in isotopic ratio 229Th/232Th. Furthermore, the pellets from these experiments were measured with direct alpha spectrometry to estimate the contents and thickness of the 229Th-rich layer formed on the pellet surface. The results of all dissolution studies showed a relatively fast release of thorium during the early stage of the experiment followed by a slow decrease in the thorium concentration and suppression of the dissolution rate as the experiments continued over 100 days. Microscopic studies revealed that the grain boundaries play a significant role in the initial release of thorium. It was also observed that the different surfaces of thorium dioxide particles behave differently either dissolving, precipitating or showing an almost inert nature, most likely due to the different surface energies of the heterogeneous material. High-resolution (sector field) inductively coupled plasma mass spectrometry (SF/HR-ICP-MS) was used for the thorium isotope analyses of leached solutions. The developed method was powerful for analysing thorium isotopes. In addition, alpha spectrometry was used for thorium analysis for comparative purposes. The alpha spectrometry yielded a lower detection limit for 229Th and a higher detection limit for 232Th than SF-ICP-MS, which was 1 x 10-12 mol for both isotopes. Thus, these methods provided comparable results for the analysed 229Th concentration. However, the chemical separation needed before alpha spectrometry is very time consuming compared to the sample preparation necessary for HR-ICP-MS. When combined with simulations, direct alpha analysis confirmed that during leaching a new layer, with a maximum thickness of 0.1 µm, formed on the surface of ThO2 pellets. Alpha spectrometry also provided interesting insight into the dissolution and co-precipitation behaviour of 229Th and 232Th decay series daughter nuclides. The surface layer contained not only 229Th and its daughters, but also an elevated concentration of daughters from the 232Th decay series, indicating that they were first released from the bulk during the leaching experiment, subsequently co-precipitating or adsorbing onto the surface of the pellet.
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(Helsingin yliopisto, 2017)The current era of bioeconomy strives to develop new, innovative products from natural raw materials in a sustainable way. In this PhD thesis, we have searched potential bioactive compounds from different parts of the neglected roots and stumps of conifer trees for high value products. Our aim was to establish deeper knowledge concerning chemical compositions of specified and defined biomass sources (roots and stumps of conifer trees) as well as the chemistry of certain natural polyphenolic compounds in different conditions. Using methods of natural products chemistry, such as solvent extraction and chromatographic separation and analysis techniques (GC-MS, HPLC-DAD/MS), we found that the root bark of Norway spruce is a rich source of stilbenoid glucosides (astringin, isorhapontin and piceid). These have structural similarities with the most studied stilbenoid, resveratrol. We also found that the stumps of Scots pine are a source of stilbenoids, pinosylvin and its derivatives. Stilbenoids are bioactive compounds and they have shown a variety of beneficial activities in studies related for example to human health. They have also shown antimicrobial and protective properties in trees and also in tests against micro-organisms. The highest concentrations of stilbenoid glucosides were found from the inner bark of the root zones closest to the stem of Norway spruce. This study also revealed that the root neck of Norway spruce is a new source of the bioactive lignan hydroxymatairesinol (HMR). Chromatographic and spectroscopic methods were developed to isolate pure stilbenoids from the bark of Norway spruce roots for further experiments. The complete structural elucidation of stilbenoids from Norway spruce was performed by HPLC-DAD-NMR. The HPLC-DAD method was further optimized to isolate stilbenoids in a semipreparative scale. The invividual stilbenoid molecules were isolated from the extracts and their photochemical stabilities (under fluorescent and UV light) were studied by HPLC-DAD, MS and NMR. Naturally-occurring trans stilbenoids undergo photochemical transformations to cis forms. However, the extended UV irradiation caused stilbenoids to form phenanthrene structures by intramolecular cyclisation. This is the first time that these new phenanthrene structures are reported to be derived from stilbenoids of spruce bark. Our results show that that the roots and stumps of conifer trees contain bioactive polyphenolic compounds, such as stilbenoids and lignans. These molecules and the compounds formed thereof may have commercial value and the information gained would offer a base platform for the possible new commercial high-value products developed from forest biomass. Our study has also provided new scientific knowledge of natural compounds and their properties that may lead to new findings and deeper understanding of the physiology and internal protection processes of plants by their bioactive secondary metabolites. Roots and stumps of conifer trees (Norway spruce and Scots pine) are a vast source of biomass containing potentially bioactive polyphenolic extractives as shown in this work, but this biomass is currently used for low-value energy production only. With already existing harvesting techniques, roots and stumps of conifer trees could be used as a source of commercially valuable biochemicals.
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(Helsingin yliopisto, 2017)Visual attention is crucial in mobile environments, not only for staying aware of dynamic situations, but also for safety reasons. However, current mobile interaction design forces the user to focus on the visual interface of the handheld device, thus limiting the user's ability to process visual information from their environment. In response to these issues, a common solution is to encode information with on-device vibrotactile feedback. However, the vibration is transitory and is often difficult to perceive when mobile. Another approach is to make visual interfaces even more dominant with smart glasses, which enable head-up interaction on their see-through interface. Yet, their input methods raise many concerns regarding social acceptability, preventing them from being widely adopted. There is a need to derive feasible interaction techniques for mobile use while maintaining the user's situational awareness, and this thesis argues that solutions could be derived through the exploration of hand-based haptic interfaces. The objective of this research is to provide multimodal interaction for users to better interact with information while maintaining proper attention to the environment in mobile scenarios. Three research areas were identified. The first is developing expressive haptic stimuli, in which the research investigates how static haptic stimuli could be derived. The second is designing mobile spatial interaction with the user's surroundings as content, which manifests situations in which visual attention to the environment is most needed. The last is interacting with the always-on visual interface on smart glasses, the seemingly ideal solution for mobile applications. The three areas extend along the axis of the demand of visual attention on the interface, from non-visual to always-on visual interfaces. Interactive prototypes were constructed and deployed in studies for each research area, including two shape-changing mechanisms feasible for augmenting mobile devices and a spatial-sensing haptic glove featuring mid-air hand-gestural interaction with haptic support. The findings across the three research areas highlight the immediate benefits of incorporating hand-based haptic interfaces into applications. First, shape-changing interfaces can provide static and continuous haptic stimuli for mobile communication. Secondly, enabling direct interaction with real-world landmarks through a haptic glove and leaving visual attention on the surroundings could result in a higher level of immersed experience. Lastly, the users of smart glasses can benefit from the unobtrusive hand-gestural interaction enabled by the isolated tracking technique of a haptic glove. Overall, this work calls for mobile interaction design to consider haptic stimuli beyond on-device vibration, and mobile hardware solutions beyond the handheld form factor. It also invites designers to consider how to confront the competition of cognitive resources among multiple tasks from an interaction design perspective.
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(Helsingin yliopisto, 2017)This thesis is motivated by two important processes in bioinformatics, namely variation calling and haplotyping. The contributions range from basic algorithms for sequence analysis, to the implementation of pipelines to deal with real data. Variation calling characterizes an individual's genome by identifying how it differs from a reference genome. It uses reads -- small DNA fragments -- extracted from a biological sample, and aligns them to the reference to identify the genetic variants present in the donor's genome. A related procedure is haplotype phasing. Sexual organisms have their genome organized in two sets of chromosomes, with equivalent functions. Each set is inherited from the mother and the father respectively, and its elements are called haplotypes. The haplotype phasing problem is, once genetic variants are discovered, to attribute them to either of the haplotypes. The first problem we consider is to efficiently index large collections of genomes. The Lempel-Ziv compression algorithms is a useful tool for this. We focus on two of its exponents, namely the RLZ and LZ77 algorithms. We analyze the first, and propose some modifications to both, to finally develop a scalable index for large and repetitive collections. Then, using that index, we propose a novel pipeline for variation calling to replace the single reference by thousands of them. We test our variation calling pipeline on a mutation-rich subsequence of a Finnish population genome. Our approach consistently outperforms the single-reference approach to variation calling. The second part of this thesis revolves around the haplotype phasing problem. First, we propose a generalization of sequence alignment for diploid genomes. Next we extend this model to offer a solution for the haplotype phasing problem in the family-trio setting (that is, when we know the variants present in an individual and in her parents). Finally, in the context of an existing read-based approach to haplotyping, we go back to basic algorithms, where we model the problem of pruning a set of reads aligned to a reference as an interval scheduling problem. We propose a exact solution that runs in subquadratic time and a 2-approximation algorithm that runs in linearithmic time.
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(Helsingin yliopisto, 2017)Northern lakes are displaying widespread ecological reorganizations in response to global change. These sensitive freshwater ecosystems are an integral component of subarctic and arctic landscapes and play a critical role in regional and global biogeochemical cycles. To understand lake ecosystem responses to direct and indirect climate forcing, and to estimate future trajectories of environmental change, we must look for past analogies of climate-lake interaction recorded in lake sedimentary archives. The present, in turn, holds the key to understand the past. This work examines patters and drivers of limnoecological change in shallow subarctic lakes across the treeline ecotone in northern Finland. A diverse set of neolimnological and paleolimnological tools and approaches were employed to explore aquatic ecosystem responses to landscape variability and direct climate forcing through space and time. Particular emphasis was placed on aquatic organic carbon that regulates vital biogeochemical processes in lakes and couples them to the global carbon cycle. To address landscape-mediated climate impact on shallow subarctic lakes, catchment controls on pelagic (lake water) and benthic (sediment) carbon pools, nutrients and productivity, periphytic algal (diatom) communities, and carbon utilization of benthic macrofauna (Cladocera) were assessed in 31 lakes spanning the treeline. To investigate long-term ecosystem development and carbon dynamics under natural and anthropogenic climate variability, two downcore sediment sequences from shallow and oligotrophic treeline lakes, covering the postglacial period (~11 500 years) and the late neoglacial (~600 years), were examined for diverse biogeochemical and paleobiological indices. Across the treeline, lake water carbon pools were fundamentally shaped by wetland influence. The adverse effect of terrestrial colored organic carbon on underwater light availability was diminished in the shallow waters and superseded by nutrient stimulation of primary production. Catchment and soil geomorphology and related hydrological processes were further identified as important controls over aquatic carbon pools, nutrient regimes, and lake water acid-base balance, carrying effects on aquatic primary production and diatom community structure. The late neoglacial paleolimnological record demonstrated a strong coupling between centennial temperature fluctuations, the structure and productivity of aquatic communities, and carbon sequestration. The changes were attributed primarily to alterations in the length of the ice cover period, and were most distinct over the Anthropocene. The postglacial sediment sequence demonstrated repeated diatom turnovers over the Holocene, attributed primarily to millennial moisture fluctuations driving changes in the depth and turbulence of the water column. Overall, the results strengthen recent notions related to the strong terrestrial-aquatic coupling as well as to the susceptibility of northern lakes to climate change, providing new aspects into the underlying processes, drivers of heterogeneity, and biotic interactions. Collectively, the findings build towards an improved understanding of the responses and resilience of northern lake ecosystems to a hierarchy of environmental drivers under the ongoing global change.
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(Helsingin yliopisto, 2017)This thesis investigates the cross-sectional association between different quantifiable societal dimensions that indicate spatially varying levels of wellbeing and development. The analysis is grounded in human geography but applies an explicitly interdisciplinary focus, combining theories and measures from economic geography, cultural studies, spatial economics, sociology and social psychology. In the empirical analyses, geographically referenced European Social Survey (ESS) data containing measures of subjective wellbeing (SWB) and human values were analysed together with objective indicators of economic performance on national and subnational scales. First, Paper I demonstrated that levels of ‘social trust’ and ‘social contact and support’, which indicate social wellbeing, and a sense of ‘competence and meaning’, which denotes personal wellbeing, are significant positive correlates with regional GDP after controlling for regional economic indicators and the spatial effects embedded in the data. Second, Paper II utilized the Human Values Scale in the ESS and studied the association between certain values and the level of economic performance. The paper demonstrated that the aggregate level of the value ‘self-direction’, which indicates independent thought, action and creativity, is a strong predictor of regional GDP. Paper II also addressed the question of rescaling and used welfare regimes as a relevant socio-historic framework of analysis. Paper III focused on the contextual effects of living in ‘Metropolitan Finland’. The results showed that the negative effect on life satisfaction of residing in the capital region of Finland is first compositional, as the population in ‘Metropolitan Finland’ is composed of individuals who appreciate the values of ‘power’ and ‘achievement’, which are themselves associated with lower life satisfaction. However, it is also contextual, as residing in the capital region moderates the positive wellbeing effect of socially focused values such as ‘benevolence’ and ‘conformity’. Finally, Paper IV added vertical detail to the intercept heterogeneity approach and asked whether changes in macroeconomic conditions, in the context of Ireland and its recent economic recession, are experienced differently in different socio-economic categories, i.e. classes. The results show that the effects of the economic crisis were not experienced equally within the population; rather, the lower strata (the lowest income quartile, manual workers and those with the lowest levels of education) were the most affected. Both the framework and results of this thesis offer new interdisciplinary insights into the geographies of subjective wellbeing and human values, a disciplinary interface that has largely remained unexplored. The results of this thesis are also relevant for regional policy-making that addresses spatial justice, territorial inequalities and uneven development. Furthermore, the findings concerning the negative wellbeing effect of metropolitan context merit attention in policies on ‘urban growth’, as they question the underlying values of such policies and their effectiveness for promoting wellbeing. Finally, the finding that macroeconomic changes have different wellbeing effects in different socio-economic layers resonates with the concept of ‘inclusive growth’, which involves promoting the distribution of opportunities and wellbeing to all segments of the population.
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(Helsingin yliopisto, 2017)Both atmospheric ice and mineral dust are considered to play important roles in our climate system through their impacts on the radiative energy budget. These impacts depend on the size, shape, composition and concentration of the ice and dust particles. However, the non-spherical shape of these particles yields uncertainties in our understanding how they interact with radiation. One of the main aims of this work is to better understand the impacts of particle size-shape distributions on radiative effects of ice and dust. For dust particles, the overall goal is to improve the treatment of optical properties of dust in global aerosol-climate models. In this thesis, the solar radiative effects of variously sized and shaped ice and dust particles are simulated using radiative transfer models. In addition, a global aerosol–climate model is used to investigate the impact of dust particle nonsphericity. Different radiative transfer models, atmospheric and surface properties etc. are used, based on the requirements of each study. Size-shape distributions of ice clouds are based on in-situ measurements, whereas for dust, carefully validated shape models of spheroids are used. This thesis offers a broad outlook on the effects of ice clouds on solar irradiances and on the angular dependence of the circumsolar radiance. In addition, it offers interesting new insight into the connections between particle morphology, cloud microphysics and cloud radiative effects. It is found that solar radiation is sensitive to the concentration of small ice crystals. In addition, comparison of simulated and measured radiation in the presence of ice clouds suggests that most natural ice crystals are not pristine, but can either have some surface roughness or other non-idealities in their shape. The results reveal that the use of spheroidal shape distributions has only small or moderate impacts on regional and global-scale direct radiative effects of dust. Consistent with this, experiments with a global aerosol–climate model indicate that the assumption of spherical shape for dust particles is not a considerable error source in climate simulations. Most probably, however, this conclusion cannot be extended to remote sensing applications. Keywords: ice crystal, mineral dust, single-scattering properties, solar radiation, circumsolar radiation, radiative transfer modelling, spheroids
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(Helsingin yliopisto, 2017)The increasing interest in both portable electronic devices and electric vehicles has given rise to a new wave of research into lithium-ion batteries. Lithium-ion batteries are the technology of choice for these applications, as they offer both high power and high energy densities. However, much research on this subject is still needed to answer the technology demands of future applications. For example, the safety concerns related to liquid electrolytes in the batteries of electric vehicles could be resolved by moving to all-solid-state batteries, which would not combust in the case of an accident. In addition, all-solid-state batteries could be manufactured into 3D structures, which would decrease the footprint area of the battery without sacrificing the amount of material. Thus, these structures would make even higher energy densities possible, which is important for example for laptops and cellphones. In addition, by combining smaller batteries with energy harvesters, such as solar cells, integrated autonomous devices could be realized. Atomic layer deposition, or ALD, is a thin film deposition method based on sequential, saturative reactions of gaseous precursors with a substrate surface. ALD generally produces highly pure films with very good thickness uniformity also in difficult, 3D substrates. Therefore, ALD should be well-suited for the deposition of Li-ion battery materials for future applications. The deposition of lithium containing materials is a fairly new avenue for ALD, the first paper being published only in 2009. It has been found that the Li-ion often bends the basic rules of ALD with its high reactivity and mobility during film growth, resulting in both unexpected reactions and film stoichiometries. This thesis provides a comprehensive review on the atomic layer deposition of lithium containing materials with a focus on the behavior of lithium in the growth process. In the experimental part, new ALD processes were developed for potential Li-ion battery materials LiF and AlF3. Both processes show reasonable ALD characteristics and produce pure films in proper deposition temperatures. In addition, conversion reactions taking place in ALD conditions were studied, and both LiF and Li3AlF6 were deposited using these reactions. The conversions were very clean, illustrated by the low impurity contents of the converted films. Lastly, the deposition of lithium containing ternary oxides was studied by heating atomic layer deposited film stacks in air. This ALD-solid state reaction -procedure resulted in pure, crystalline films of LiTaO3, LiNbO3 and Li2TiO3.
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(Helsingin yliopisto, 2017)This dissertation belongs to the field of harmonic analysis, which is a subfield of mathematical analysis. It consists of an introductory part and four research articles. Two of the articles study testing characterizations of two-weight inequalities and the other two study local Tb theorems. An operator, such as a singular integral or a dyadic integral operator, satisfies a two-weight inequality if it is bounded between two weighted function spaces Testing characterizations show that to have the two-weight inequality it suffices to test the operator with a very restricted class of functions. Local Tb theorems provide criteria for boundedness of a given operator, usually of a singular integral or a square function. The basic idea is similar to testing of two-weight inequalities: to have boundedness it is enough to test the operator with suitable test functions. Nazarov, Treil and Volberg characterized two-weight inequalities of well localized operators between two L^2-spaces in terms of so-called Sawyer type testing conditions. The first article in the thesis introduces a quadratic testing condition and shows that it can be used in place of the Sawyer type testing condition to obtain an L^p-version of the mentioned L^2-result. The second article introduces a quadratic version of the Muckenhoupt type two-weight A_p condition on the weights. It is shown that if the weights satisfy the quadratic A_p condition, and a dyadic shift operator satisfies the quadratic testing conditions in L^p, then a certain quantitative two-weight estimate holds. This is an L^p-version of the L^2-result by Hytönen, Pérez, Treil and Volberg. The third article introduces a new method to prove local Tb theorems. It relies on ``big piece thinking'', which appears in connection with other problems in mathematical analysis, and on the non-homogeneous good lambda method of Tolsa. By using the new method, the article improves known results concerning local Tb theorems for vertical square functions in the upper half space. The final article studies conical square functions which are defined with respect to a general closed subset of the Euclidean space. The method from the third article is applied to prove a corresponding local Tb theorem in this set-up.
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(Helsingin yliopisto, 2017)A monodromy representation represents a branched covering map between manifolds as a factor of an orbit map. This factorization arises from the monodromy of the branched covering map. We call the domain of the orbit map the monodromy space of the branched covering map. In this thesis a manifold is a connected second countable Hausdorff space that is locally homeomorphic to the Euclidean space. A branched covering map between manifolds is an open, continuous and discrete map. A branch point of a branched covering map is a point at which the map fails to be a local homeomorphism, and the branch set is the set of branch points. The first research question of this thesis considers new existence results of monodromy representations: In what extent does Bersteins and Edmonds construction of a monodromy representation generalize to branched covering maps between manifolds? In article [A] we first consider a class of branched covering maps between manifolds that is natural for the construction. Then we introduce a characterization for the existence of a monodromy representation within this class of maps. The second research question concerns the properties of the monodromy space: What properties can we expect from the monodromy space as a topological space? The monodromy space is a locally connected Hausdorff space by construction. In article [A] we provide an example to show that the monodromy space is not in general a locally compact space. In article [C] we provide further examples to show that a monodromy space that is a locally compact space, is not in general a manifold, a locally contractible space or a cohomology manifold. The third research question concerns new applications of monodromy representations in the study of branched covering maps between manifolds: What consequences does the existence of a monodromy representation have on the branch set of a branched covering map between manifolds? The branch set has by Väisälä codimension more or equal to two. A classical conjecture of Church and Hemmingsen states that the codimension of the branch set is strictly two for a branched covering map from the three sphere to a three sphere. We show together with Pankka in article [B] two partial results in the direction of this conjecture.
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(Helsingin yliopisto, 2017)Eco-efficient biotechnological applications are important innovations for modern industrial developments, such as production of chemicals and fuels from renewable biomass. Lignocellulosic biomass is the only sustainable organic resource that can be converted to both energy and various value-added products. The effective use of wood and plants for feedstock in biorefineries is in most cases dependent on the plant cell wall recalcitrance and especially the extent of lignification of the cell wall. Oxidative enzymes such as laccases and manganese peroxidases (MnPs), provide interesting possibilities for plant biomass modification as they are the key catalysts in modification and degradation of the most recalcitrant component of the lignocellulose biopolymers, lignin, in nature. Both peroxidases and laccases exhibit low substrate specificity and produce organic radicals through one-electron abstraction reactions. In many cases these enzymes require low molecular weight co-substrates to mediate oxidation to the more recalcitrant parts of lignin polymer. In the first study of this thesis, various types of lignin model compounds were investigated both as mediators and as final targets to screen their effect and potential in laccase-catalyzed oxidation reactions. Especially acetosyringone and methyl syringate were found to mediate the laccase-catalyzed oxidation even with low-redox potential laccase that generally shows only fair oxidation activity on lignocellulosic oxidation. Secondly, in two of the articles, the mediating rate and effectivity were enhanced by using high redox potential laccases and suitable reaction conditions to retain the stability of the mediator. Oxidation potentials, pH and chemical stability of the mediator were found to affect the oxidation efficiency. These simple phenolics were, for the first time, also proved to mediate the MnP-catalyzed reactions of non-phenolic compounds. The problematic stability of peroxidases was circumvented by utilizing reaction system with no external addition of hydrogen peroxide. Finally, to prove the effect on polymer material a new reaction set-up was developed for oxidation of synthetic lignin (DHP, dehydrogenation polymer) and the structural analysis of the oxidized polymers showed clear modifications in the polymer outcome. In all cases, mediated reactions gave selective alpha-oxidation products of benzylic alcohol moieties, the prevailing structural moiety in lignin. These oxidations provide valuable intermediates for further treatments in various lignin valorization processes. In the near future, this oxidative laccase-mediator oxidative system will be explored in an EU Horizon 2020 project for valorization of biorefinery lignin by combination of biotechnical and chemical means to added-value products such as marine biofuel, engine octane boosters and valuable low-molecular weight chemicals.
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(Helsingin yliopisto, 2017)This thesis investigates interactions between solar wind and the magnetosphere of the Earth using two global magnetospheric simulation models, GUMICS-4 and Vlasiator, which are both developed in Finland. The main topic of the thesis is magnetic reconnection at the dayside magnetopause, its drivers and global effects. Magnetosheath mirror mode waves and their evolution, identification and impacts on the local reconnection rates at the magnetopause are also discussed. This thesis consists of four peer-reviewed papers and an introductory part. GUMICS-4 is a magnetohydrodynamic model solving plasma as a single magnetized fluid. Vlasiator is the world s first global magnetospheric hybrid-Vlasov simulation model, which solves the motion of ions by describing them as velocity distribution functions, whereas electrons are described as a charge neutralizing fluid. Vlasiator is able to solve ion scale physics in a global scale simulation. However, it is computationally heavy and the global simulations are currently describing Earth s magnetosphere only in two spatial dimensions, whereas the velocity space is three dimensional. This thesis shows that magnetic reconnection at the dayside magnetopause is controlled by several factors. The impact of dipole tilt angle and sunward component of the interplanetary magnetic field on magnetopause reconnection is investigated with a set of GUMICS-4 simulations. Using Vlasiator simulations, this thesis shows that local reconnection rate is highly variable even during steady solar wind and correlates well with an analytical model for 2D asymmetric reconnection. It is also shown that the local reconnection rate is affected by local variations in the magnetosheath plasma. Fluctuations in the magnetosheath parameters near X-lines are partly generated by mirror mode waves that are observed to grow in the quasi-perpendicular magnetosheath. These results show that that the local reconnection rate at the X-lines is affected not only by the fluctuations in the inflow parameters but also by reconnection at nearby X-lines. Outflow from stronger X-lines pushes against the weaker ones and might ultimately suppress reconnection in the weaker X-lines. Magnetic islands, 2D representations of FTEs, form between X-lines in the Vlasiator simulations. FTEs propagate along the dayside magnetopause driving bow waves in the magnetosheath. The bow waves propagate upstream all the way to the bow shock causing bulges in the shock, from which solar wind particles can reflect back to the solar wind causing local foreshocks. The overall conclusion of this thesis is that the ion scale kinetic physics is important to accurately model the solar wind magnetosheath magnetopause interactions. Vlasiator results show a strong scale-coupling between ion and global scales: global scale phenomena have an impact on the local physics and the local phenomena may have unexpected impacts on the global dynamics of the magnetosphere. Neglecting the global scales in local ion scale simulations and vice versa may therefore lead to incomplete description of the solar wind magnetosphere interactions.
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(Helsingin yliopisto, 2017)The experiments at the Large Hadron Collider (LHC) have confirmed that the Standard Model (SM) is a good description of particle physics at the electroweak scale. The Standard Model is still incomplete, since it does not explain e.g. neutrino masses, dark matter, dark energy or gravity. Supersymmetry is a well motivated way to extend the Standard Model. The minimal supersymmetric Standard Model (MSSM) has become somewhat fine-tuned after the first run of the LHC and therefore the detailed study of nonminimal supersymmetric models is highly motivated. We studied phenomenological implications of some nonminimal supersymmetric models especially in the light of the recent discovery of a Higgs boson. Our studies focused on supersymmetry without R-parity and left-right symmetric supersymmetric models. In the MSSM a 125 GeV Higgs requires rather heavy superpartners. In nonminimal models the Higgs mass can be lifted by contributions from new particles at tree-level, loop-level or by mixing effects. We found that if we introduce spontaneous R-parity violation, the mixing between the SM-like Higgs and a right-handed sneutrino can increase the mass of the SM-like Higgs if the sneutrino-like state is lighter than 125 GeV. One does not need as heavy superpartners as in the MSSM and thus fine-tuning is not as severe. If the Higgs mass gets additional contributions, the squarks of the third generation can be more easily within the reach of the LHC. If R-parity is not imposed, the squarks can have new decay modes, which can have a large branching fraction. As an example we studied a model, where R-charges are identified with the lepton number and found that the discovery potential for the stop decaying to a bottom quark and a positron is well beyond 1 TeV squark masses. In left-right supersymmetry we studied the Higgs decay modes and the option of having a right-handed sneutrino as a dark matter candidate. We found that a loop-induced mixing of the bidoublets can either enhance or suppress the Higgs coupling to bottom quarks and thus change the signal strengths considerably. However, in the scan there was also a large number of points, where the couplings behaved close to those of the SM. The right-handed sneutrino is a part of a doublet in left-right symmetric models. We found that sneutrinos may annihilate via a D-term coupling to the Higgs and produce the observed relic density. If we assume the gauge coupling of the right-handed gauge interactions to be the same as for the left-handed ones, we were able to predict a range of masses for the sneutrino. We also showed that with 100 inverse femtobarns we could get a signal of superpartners from the sleptonic decays of the right-handed W-boson, if its mass is below 3 TeV.
