Matemaattis-luonnontieteellinen tiedekunta

 

Recent Submissions

  • Toivonen, Jaakko (Helsingin yliopisto, 2017)
    In this thesis we use the framework of adaptive dynamics and bifurcation analysis to study evolution with a spatially explicit population model in an abiotic environment that changes over geological timescales. Essentially, this process models the fossil record. In accordance with previous studies, we find that branching on an environmental gradient occurs when the environmental gradient is not too steep or shallow. Even though branching on a steep gradient is not possible for a monomorphic population, we find an interesting evolutionary hysteresis effect: depending on environmental history it is possible for a polymorphic population to evolve and inhabit a steep environmental gradient on which monomorphic branching does not occur. Further, we find that it is typically intermediate phenotypes that undergo branching. Here evolution occurs through small mutational steps and via an invasion-substitution sequence. However, over the timescales of the fossil record this gradual evolution may appear as punctuated. In a slowly changing environment intermediate phenotypes are also more prone to extinction, whereas in a fast changing environment extreme phenotypes are seen to be in greater danger. We use this modeling approach to study a partially unexplained pattern of diversification of hoofed mammals in Eurasia during the Late Miocene (11-5 Ma). We also use game theoretical methods to study the evolution of trade-offs: another pattern ubiquitous in nature. Specifically, we model an annual plant population and study the correlation of seed size and germination time. We do not assume any physiological constraints on the production of seeds of any combination of size and germination time. However, we find that typically an Evolutionarily Stable Strategy is such that a correlation emerges between the two. This raises the general question whether trade-offs observed in nature are caused by physiological constraints or whether they are just implementations of an evolutionarily beneficial strategy.
  • Taka, Maija (Helsingin yliopisto, 2017)
    Detecting trends in stream water quality is one of the key objectives of environmental monitoring. Identifying factors controlling stream water pollutants is challenging due to the diversity of potential sources, pathways, and processes. Natural processes regulating the water quality of a watershed are often affected by anthropogenic activities, resulting in the redistribution of runoff from base flow to storm flow and the introduction of new pollutant sources. Despite the observed consequences of urbanization, a lack of understanding of the factors simultaneously controlling water quality is among the biggest gaps in our current knowledge of hydrogeography. Moreover, prevailing discussions of land-cover effects often neglect the potential contribution of other factors, such as surficial deposits, in stream water concentrations. This thesis aims to 1) examine the most influential watershed properties determining spatial variation in stream water quality; 2) identify key water quality and watershed variables controlling stream biotic responses (i.e. diatom community composition); 3) investigate the effects of multiscale temporal variation on urban runoff in cold climatic regions; and 4) evaluate whether advanced statistical methods are applicable in hydrogeographical modeling of small watersheds. To fulfill these objectives, spatial watershed-scale analyses were conducted using modern non-parametric approaches and theory-driven methods such as structural equation modeling. This thesis is based on unique data sets of both multibasin and multiyear sampling and spatial data from the Helsinki region, southern Finland. A combination of GIS-based approaches and statistical analyses revealed significant links and novel insights into complex relationships between water quality and spatial biogeophysical properties of the surrounding landscape. The importance of land cover was emphasized throughout the thesis. Under base flow conditions the significance of soil type was mainly controlled by land cover. Further, this thesis demonstrates how land cover and stream water quality strongly determine the spatial assemblages of aquatic biota, as elevated pollutant levels were linked to decreased species richness and dominance of more tolerant species of diatom taxa. From a temporal perspective, the results suggest that urban runoff pollution is a chronic phenomenon, and is controlled by both runoff volume (summer) and pollutant sources (winter). Both the divergent temporal behavior and dominant role of diffuse pollution sources indicated challenges for stream water management practices. Based on the observed substance levels, year-round runoff treatment in urban areas is highly recommended. Finally, this thesis increases our knowledge of stream water quality variation in space and time. In this thesis, key local phenomena in contemporary hydrogeography were identified with a spatial modeling framework. The inclusion of indirect effects into the models improved our understanding of these systems, thus emphasizing the importance of simultaneously studying multiple concurrent processes.
  • Kietäväinen, Riikka (Helsingin yliopisto, 2017)
    Within Precambrian continental shields, saline, gas-rich groundwaters are found in all over the world from bedrock fractures and pore spaces in the upper crust. Several processes, from seawater evaporation or freezing followed by infiltration to water rock interaction, have been suggested to be responsible for the characteristic features of these waters. In addition to reactions between water and the bedrock, active microbial communities inhabiting these waters, i.e. the deep biosphere, may play a significant role in shaping their surroundings by biogeochemical reactions, especially by contributing to the deep carbon cycle. The origin and evolution of deep groundwater in the 2.5 km deep Outokumpu Deep Drill Hole in eastern Finland was investigated using geochemical and isotopic methods. The sample material included water and gas derived from the drill hole by tube sampling, pumping and pressurized methods, as well as fracture minerals. Similar results were obtained for water samples using different sampling techniques. However, as uncontrolled degassing took place during tube sampling and pumping, it is suggested that pressurized methods should be used for gas sampling. Five water types were discerned along the drill hole, which reflect changes in lithology and indicate isolation from the surface and from each other within the Outokumpu bedrock. An evolutionary model was proposed that includes precipitation and infiltration of meteoric water at warmer than present climatic conditions, a shift in the stable isotopic composition of water and an increase in salinity through water rock interaction between virtually stagnant groundwater and the bedrock, and both the abiotic and biotic formation of hydrocarbons. Two independent lines of evidence from water stable isotopes and the accumulation of radiogenic and nucleogenic noble gases indicated isolation of the Outokumpu Deep Drill Hole groundwaters from the meteoric water cycle from the Eocene-Miocene epochs, placing the evolutionary model in the time frame of millions to tens of millions of years. The results shed light on how deep groundwaters have evolved in geochemical and microbiological processes through time and space. Furthermore, they emphasise the complexity of these environments, as they are being increasingly utilised for underground construction, and provide background information for assessment of the long-term safety of nuclear waste disposal.
  • Venieri, Laura (Helsingin yliopisto, 2017)
    In this dissertation we define a generalization of Kakeya sets in certain metric spaces. Kakeya sets in Euclidean spaces are sets of zero Lebesgue measure containing a segment of length one in every direction. A famous conjecture, known as Kakeya conjecture, states that the Hausdorff dimension of any Kakeya set should equal the dimension of the space. It was proved only in the plane, whereas in higher dimensions both geometric and arithmetic combinatorial methods were used to obtain partial results. In the first part of the thesis we define generalized Kakeya sets in metric spaces satisfying certain axioms. These allow us to prove some lower bounds for the Hausdorff dimension of generalized Kakeya sets using two methods introduced in the Euclidean context by Bourgain and Wolff. With this abstract setup we can deal with many special cases in a unified way, recovering some known results and proving new ones. In the second part we present various applications. We recover some of the known estimates for the classical Kakeya and Nikodym sets and for curved Kakeya sets. Moreover, we prove lower bounds for the dimension of sets containing a segment in a line through every point of a hyperplane and of an (n-1)-rectifiable set. We then show dimension estimates for Furstenberg type sets (already known in the plane) and for the classical Kakeya sets with respect to a metric that is homogeneous under non-isotropic dilations and in which balls are rectangular boxes with sides parallel to the coordinate axis. Finally, we prove lower bounds for the classical bounded Kakeya sets and a natural modification of them in Carnot groups of step two whose second layer has dimension one, such as the Heisenberg group. On the other hand, if the dimension is bigger than one we show that we cannot use this approach.
  • Weigang, Helene Camilla (Helsingin yliopisto, 2017)
    This thesis theoretically investigates dispersal evolution in a wider ecological context. It factors in ecological relevant dependencies e.g. trade-offs or spatial heterogeneity, and allows coevolutionary interactions between immigration and other traits. It extends well-known models to include more biological realism, reveals novel evolutionary mechanisms and helps to understand the complex dispersal patterns more accurately. In particular, this work studies the evolution of dispersal, i.e., natal emigration when it is under a trade-off with fecundity. Furthermore, dispersal is divided into its three phases and hence studied as emigration, transfer and immigration. Emigration and immigration are made dependent on the local conditions experienced by the individuals: the patch types. The coevolution of patch-type dependent immigration is investigated alone, but also the coevolution of patch-type dependent immigration and patch-type dependent emigration or local adaptation is studied. The evolutionary framework was chosen to be adaptive dynamics, a way of describing the long-term evolutionary outcomes of single populations that can lead to evolutionary diversification of strategies.
  • Partanen, Lauri (Helsingin yliopisto, 2017)
    Sulfuric and hydrochloric acids participate in several important chemical processes occurring in the atmosphere. Due to its tendency to react with water molecules, sulfuric acid is an important factor in cloud formation and related phenomena. Hydrochloric acid is heavily implicated in stratospheric ozone depletion because of its role as a temporary reservoir for chlorine radicals. In this thesis, the thermodynamics and dynamics of these two acids are investigated. The dynamic part focuses on the chemical processes following collision of HCl on water and amorphous ice surfaces at different temperatures. By utilizing ab initio molecular dynamics, it is observed that the surface temperature and the initial kinetic energy of the HCl molecule have important and not wholly overlapping effects on its ionization behaviour. The results add to the understanding of hydrochloric acid dissociation on water surfaces in various parts of the atmosphere, potentially illuminating new pathways for related chemical reactions, such as the formation of ClNO on amorphous ice surfaces. The thermodynamic studies revolve around the impact of multiple low-lying stable conformers, or global anharmonicity, on the thermodynamic properties. The studies for this part focus on complexes of sulfuric acid, especially sulfuric acid monohydrate. Due to the relatively small size of the monohydrate, high-level ab initio methods can be employed to obtain accurate values for its thermodynamic properties, thus providing a reliable basis for comparison with less accurate approaches. New ways of accounting for global anharmonicity are developed both for small- and medium-sized clusters. For small clusters, an approximation is presented where the large amplitude motions connecting different conformers are treated separately from the rest of the vibrations, resulting in direct quantum mechanical accounting of the different conformers. In the case of medium-sized clusters, an equation based on statistical mechanics is derived to replace the erroneous Boltzmann averaging formula that has seen wide use in the literature.
  • Zou, Yuan (Helsingin yliopisto, 2017)
    Model selection is one of the fundamental tasks in scientific research. In this thesis, we addresses several research problems in statistical model selection, which aims to select a statistical model that fits the data best. We focus on the model selection problems in Bayesian networks and logistic regression from both theoretical and practical aspects. We first compare different model selection criteria for learning Bayesian networks and focus on the Fisher information approximation (FIA) criterion. We describe how FIA fails when the candidate models are complex and there is only limited data available. We show that although the Bayesian information criterion (BIC) is a more coarse than FIA, it achieves better results in most of the cases. Then, we present a method named Semstem, based on the structural expectation maximization algorithm, for learning stemmatic trees as a special type of Bayesian networks, which model the evolutionary relationships among historical manuscripts. Semstem selects best models by the maximum likelihood criterion, which is equivalent to BIC in this case. We show that Semstem achieves results with usually higher accuracies and better interpretability than other popular methods when applied on two benchmark data sets. Before we turn to the topic of learning another type of Bayesian networks, we start with a study on how to efficiently learn interactions among variables. To reduce the search space, we apply basis functions on the input variables and transform the original problem into a model selection problem in logistic regression. Then we can use Lasso to select a small set of effective predictors out of a large set of candidates. We show that the Lasso-based method is more robust than an earlier method under different situations. We extend the Lasso-based method for learning Bayesian networks with local structure, i.e. regularities in conditional probability distributions. We show that our method is more suitable than some classic methods that do not consider local structure. Moreover, when the local structure is complex, our method outperforms two other methods that are also designed for learning local structure.
  • Vira, Julius (Helsingin yliopisto, 2017)
    Atmospheric chemistry and transport models are used for a wide range of applications which include predicting dispersion of a hazardous pollutants, forecasting regional air quality, and modelling global distribution of aerosols and reactive gases. However, any such prediction is uncertain due to inaccuracies in input data, model parametrisations and lack of resolution. This thesis studies methods for integrating remote sensing and in-situ observations into atmospheric chemistry models with the aim of improving the predictions. Techniques of data assimilation, originally developed for numerical weather prediction, are evaluated for improving regional-scale predictions in two forecast experiments, one targeting the photochemical pollutants ozone (O3) and nitrogen dioxide (NO2), the other targeting sulphur dioxide (SO2). In both cases, assimilation of surface-based air quality monitoring data is found to initially improve the forecast when assessed on monitoring stations not used in assimilation. However, as the forecast length increased, the forecast converged towards the reference simulations where no data assimilation was used. The relaxation time was 6-12 hours for SO2 and SO2 and about 24 hours for O3. An alternative assimilation scheme was tested for SO2. In addition to the initial state of the forecast, the scheme adjusted the gridded emission fluxes based on the observations within the last 24 hours. The improvements due to adjustment of emissions were generally small but, where observed, the improvements persisted throughout the 48 hour forecast. The assimilation scheme was further adapted for estimating emission fluxes in volcanic eruptions. Assimilating retrievals of the Infrared Atmospheric Sounding Interferometer (IASI) instrument allowed reconstructing both the vertical and horizontal profile of SO2 emissions during the 2010 eruption of Eyjafjallajökull in Iceland. As a novel feature, retrievals of plume height were assimilated in addition to the commonly used column density retrievals. The results for Eyjafjallajökull show that the plume height retrievals provide a useful additional constraint in conditions where the vertical distribution would otherwise remain ambiguous. Finally, the thesis presents a rigorous description and evaluation of a numerical scheme for solving the advection equation. The scheme conserves tracer mass and non-negativity, and is therefore suitable for regional and global atmospheric chemistry models. The scheme is particularly adapted for handling discontinuous solutions; for smooth solutions, the scheme is nevertheless found to perform comparably to other state-of-art schemes used in atmospheric models.
  • Votsis, Athanasios (Helsingin yliopisto, 2017)
    As the adaptation of cities to climate change is increasingly overlapping sustainable urban development, the necessity to harmonize climate-proofing with economic objectives becomes ever clearer. Climate-sensitive ecological risks and amenities, and their role in markets and urban planning, are central in this issue. This research explores the reaction of urban housing markets to changes related to green amenities and flood risks; deepens the understanding of complex spatial processes, in housing markets and urban growth, that relate to the implementation of sustainable adaptation strategies; and develops advanced spatial modelling methodology that renders urban economic analysis better suitable to address questions of sustainable and climate-proof urban planning. The results demonstrate that physical or behavioral planning interventions surrounding climate-sensitive ecological risks and amenities generate economic benefits via multiple channels, when attuned with market mechanisms. This is an important building block in synchronizing climate-proofing with economic development objectives, therefore facilitating urban adaptation that is also sustainable. The synchronization requires an evidence-based understanding of the effects linked to particular interventions, at concrete locations and spatiotemporal scales. The overall message is that, while trade-offs are unavoidable, if green cities maintain agglomeration benefits, ensure increased information flows about ecological risks and amenities, while implementing amenities in a spatially parameterized manner, they are able to achieve both climate-proofing and sustainability objectives. The thesis consists of five quantitative analysis articles, while the introductory chapter synthesizes the results in the context of urban planning, spatial economics, and climate change adaptation. The first three articles apply empirical microeconometric methodologies (spatial hedonic and difference-in-differences analysis) to explore the response of housing markets to changes in green infrastructure and to policy instruments related to flood risk information. The fourth and fifth articles apply spatial complexity methods (cellular automata, fractal geometry) to extend the intuitions of microeconometric estimations into dynamic spatial processes in housing prices and urban growth. The five articles use environmental-economic datasets developed by this dissertation research, covering the urban region of Helsinki (Helsinki, Espoo, and Vantaa) and the cities of Pori and Rovaniemi.
  • Kieloaho, Antti-Jussi (Helsingin yliopisto, 2017)
    Low-molecular-weight alkyl amines are reactive organic nitrogen compounds that are im- portant precursors in secondary aerosol formation. Atmospheric aerosols have direct and indirect effects on Earth's climate system. Alkyl amines are emitted from marine and terrestrial ecosystems, agricultural activities and other anthropogenic sources. In terrestrial ecosystems, the quantities in the different parts of an ecosystem and formation processes are not well understood. Alkyl amine soil concentration and biosphere atmosphere exchange measurements are scarce. The main focus of this thesis is to determine concentrations of alkyl amines in ambient air in boreal forest and urban area, and further identify possible sources and reservoirs of alkyl amines in boreal forest. The main results presented in the thesis consist of a timeseries of gas- phase concentrations of alkyl amines measured over several months, concentrations of alkyl amines in the soil and fungal biomass, and an emission estimation based on the measured concentrations. Alkyl amines were studied in two northern latitude environments: in a boreal Scots pine (Pinus sylvestris L.) forest at the SMEAR II station in Hyytiälä and in an urban background area at the SMEAR III station in Helsinki. To quantify ambient air concentrations of alkyl amines in these environments, sample collection and analytical methods were developed. Ambient air concentrations of alkyl amines were measured from May to October 2011 in the forest site and from May to August 2011 in the urban site. The effect of the measured ambient air concentrations of alkyl amines on the local air chemistry was also assessed together with aromatic hydrocarbons and terpenoids. To assess boreal forest soil as a source of alkyl amines, a pot-scale experiment was set up. In the experiment Scots pine seedlings were grown on humus soil collected from the forest site, and the effects of Scots pine and soil organic matter (SOM) degrading enzymes on alkyl amine soil concentrations were studied. In addition, fungal strains common in boreal forest soils were cultured, and the alkyl amine concentrations in the grown fungal biomass were quanti- fied. The role of boreal forest soil as a source or as a sink of atmospheric alkyl amines was studied using a gradient-diffusion approach. In the approach, the soil atmosphere exchange of selected alkyl amines was estimated. This was done by describing dissolution/volatilisation on water and transport processes, and utilizing the quantified soil and ambient air gas-phase concentrations of the selected alkyl amines found in the studied boreal forest. The gas-phase concentrations of alkyl amines in ambient air were found to be higher in the forest site than in the urban site. In the forest site, the atmospheric concentrations appeared to be linked to soil and vegetation activity based on the seasonal course of the measured alkyl amines. Litterfall, a phenological event, coincides with the concentration maxima of some of the measured alkyl amines. In the pot-scale experiment, the SOM degrading enzymes were found to have no effect on the soil concentrations of alkyl amine while the presence of Scots pine was found to have an effect on the concentrations of some of the measured alkyl amines. The soil concentrations of alkyl amines were found to be lower than those measured from the fungal biomass. The most abundant fungal groups (ectomycorrhizal and saprotrhopic fungi) in the forest soil contained the highest quantities of alkyl amines revealing that fungal biomass may be an important reservoir of alkyl amines in boreal forest soil. Based on the flux estimate, the boreal forest soil was found to act as both a source and a sink of alkyl amines. The direction of the flux was dependent on the studied alkyl amines and environmental conditions in the forest site. Soil pH was found to be one of the most critical factors determining the direction of the flux between the soil and the atmosphere.
  • Prank, Marje (Helsingin yliopisto, 2017)
    Atmospheric composition has strong influence on human health, ecosystems and also Earth's climate. Among the atmospheric constituents, particulate matter has been recognized as both a strong climate forcer and a significant risk factor for human health, although the health relevance of the specific aerosol characteristics, such as its chemical composition, is still debated. Clouds and aerosols also contribute the largest uncertainty to the radiative budget estimates for climate projections. Thus, reliable estimates of emissions and distributions of pollutants are necessary for assessing the future climate and air-quality related health effects. Chemistry-transport models (CTMs) are valuable tools for understanding the processes influencing the atmospheric composition. This thesis consists of a collection of developments and applications of the chemistry-transport model SILAM. SILAM's ability to reproduce the observed aerosol composition was evaluated and compared with three other commonly used CTM-s in Europe. Compared to the measurements, all models systematically underestimated dry PM10 and PM2.5 by 10-60%, depending on the model and the season of the year. For majority of the PM chemical components the relative underestimation was smaller than that, exceptions being the carbonaceous particles and mineral dust - species that suffer from relatively small amount of available observational data. The study stressed the necessity for high-quality emissions from wild-land fires and wind-suspended dust, as well as the need for an explicit consideration of aerosol water content in model-measurement comparison. The average water content at laboratory conditions was estimated between 5 and 20% for PM2.5 and between 10 and 25% for PM10. SILAM predictions were used to assess the annual mortality attributable to short-term exposures to vegetation-fire originated PM2.5 in different regions in Europe. PM2.5 emitted from vegetation fires was found to be a relevant risk factor for public health in Europe, more than 1000 premature deaths per year were attributed to vegetation-fire released PM2.5. CTM predictions critically depend on emission data quality. An error was found in the EMEP anthropogenic emission inventory regarding the SOx and PM emissions of metallurgy plants on the Kola Peninsula and SILAM was applied to estimate the accuracy of the proposed correction. Allergenic pollen is arguably the type of aerosol with most widely recognised effect to health. SILAM's ability to predict allergenic pollen was extended to include Ambrosia Artemisiifolia - an invasive weed spreading in Southern Europe, with extremely allergenic pollen capable of inducing rhinoconjuctivitis and asthma in the sensitive individuals even in very low concentrations. The model compares well with the pollen observations and predicts occasional exceedances of allergy relevant thresholds even in areas far from the plants' habitat. The variations of allergenicity in grass pollen were studied and mapped to the source areas by adjoint computations with SILAM. Due to the high year-to-year variability of the observed pollen potency between the studied years and the sparse observational network, no clear geographic pattern of pollen allergenicity was detected.
  • Cole, Elizabeth (Helsingin yliopisto, 2017)
    The universe is populated with magnetically active stars. This magnetic activity is thought to be generated by dynamos operating in turbulent stellar convection zones, a process by which kinetic energy is converted into magnetic energy. The solar dynamo is but one dynamo type possible for stars. Rapidly rotating late-type stars are observed to have large spots, activity cycles, flip-flops, and active longitudes, all indicating a different dynamo mechanism may be responsible. Numerical simulations provide a tool for better understanding some of the mechanisms responsible for these dynamos. In this thesis, direct numerical simulations in spherical wedges are used to study dynamo mechanisms in the stellar convection zone. These spherical wedges are used to investigate the dependence of the resulting magnetic field on input parameters such as the density stratification and rotation rate. Mean-field models are used to evaluate the assumption that the wedges can be used to approximate full spheres. As rotation increases, differential rotation decreases in the models, in agreement with observations where more rapidly rotating stars have smaller estimates for differential rotation. As density stratification approaches more realistic values, a lat- itudinal dynamo wave with equatorward propagation is found. The impact of the domain size in the azimuthal direction on the results is explored. When the domain size is increased to 2pi in the azimuthal direction, a non-axisymmetric m = 1 mode is excited. This non-axisymmetry is reminiscent of the field configurations of rapidly rotating late-type stars. The azimuthal dynamo wave rotates nearly independently of latitude and depth, and its rotation rate is slower than that of the mean rotation of the model. This azimuthal dynamo can provide a possible explanation for the observed rotational difference of spots from the mean rotation observed on stars. The wedges use the perfect conductor boundary conditions at the latitudinal boundary to compensate for the omission of polar regions due to the time step becoming prohibitively small there. Simple mean-field models with only a latitudinal extent and perfectly conducting boundaries do not oscillate when the model is extended to the poles. Thus oscillations near the polar region may be an artifact of the boundary condition. However, when the alpha effect from mean-field dynamo theory and magnetic diffusivity are concentrated towards lower latitudes, oscillatory solutions with equatorward migration are found. When sufficient shear is added, oscillatory solutions are again found, and the Parker-Yoshimura rule for latitudinal dynamo wave propagation is obeyed. It is concluded that numerical simulations where the alpha effect and diffusivity are found to be stronger at lower latitudes and simulations with sufficient shear are considered good approximations of full spheres. These numerical simulations are put into context with stellar observations. Two young solar analogs are selected, V352 Canis Majoris and LQ Hydrae. V352 CMa is considered an active star, while LQ Hya is classified as a super-active star. The continuous period search method is applied to the low-amplitude light curves of V352 CMa. Stable active longitudes with rotation periods of 7.157 days are found. This is faster than the mean rotation of 7.24 days. Such active longitudes may be due to the underlying magnetic structure with azimuthal dynamo waves competing with differential rotation. LQ Hya rotates even more rapidly with a rotation period of only 1.600 days. A carrier period is selected of 1.605 days using the D2 statistical analysis. Primary and secondary light curve minima are found with the carrier fit analysis. No stable active longitudes are found, instead, there is only a short period spanning a few years where an active longitude may exist, but the rotation period is poorly defined. Several possible flip-flop events are identified. The azimuthal dynamo waves in numerical simulations with comparable rotation rates have a similar chaotic nature. The Doppler Imaging technique is applied to LQ Hya to examine the latitudinal spot structure. Spots at high and low latitudes are in agreement with the bimodal structure of the D2 statistic used in the carrier fit analysis. Temperature maps of LQ Hya spanning four years show an increase and a decrease in spot coverage, but no cycle can be found. Because LQ Hya is a rapidly rotating star, differential rotation is estimated to be very small. The azimuthal dynamo wave presents a new possible explanation for the jumps and trends of the spots in observations of this star.
  • Holopainen, Jani (Helsingin yliopisto, 2017)
    Bone is a fibrous nanocomposite material with a complex hierarchical system of different macro-, micro- and nanostructures. The structure elegantly supports the bone cell functions and facilitates bone remodeling by cellular activity. Injuries and diseases, e.g. osteoporosis, can cause bone fractures and loss that need to be treated with orthopedic implants. The global orthopedic market was estimated at $30 500 000 000 in 2012 and predicted to grow rapidly. A substantial amount of this goes to revision surgery due to implant failures. This not only causes unnecessary costs and work but reduces the quality of life for patients. The key for improving the performance of current implants lies in optimizing both the surface chemistry and structure from macro- to nanoscale. At best bone defects can be treated with bone scaffolds that induce formation of new bone via cellular functions and are degraded by the body thus evading the need for implant removal surgery. However, combining the favorable mechanical, structural and chemical properties poses challenges for the design and preparation methods used for bone implants and scaffolds. The aim of this work was to investigate the preparation of thin film and fibrous biomaterials for bone implants and scaffolds. New processes were developed for various biomaterials and their properties were thoroughly characterized. A method to convert CaCO3 nanostructures to nanocrystalline hydroxyapatite (HA) by treatment in phosphate solution was used to prepare HA thin films and fibers from atomic layer deposited (ALD) and electrospun CaCO3, respectively. HA fibers were also fabricated conventionally by annealing electrospun composite fibers that incorporated Ca and P precursors. Biocomposite fibers of HA nanoparticles and polylactic acid (nHA/PLA) were directly electrospun. These different nanofibers are highly interesting for bone scaffolds owing to their high surface area and the structural similarity to the fibrous nanostructure found in bone. However, conventional electrospinning is limited by its modest production rate. A needleless twisted wire electrospinning (NTWE) setup was developed to increase the production rate and was studied for the preparation of HA fibers for the bone scaffolds. Solution blow spinning (SBS) and electroblowing (EB) of HA were studied as other upscaling alternatives. Promising results were obtained in cell culture studies with the different materials. The electrospun materials could find use in fibrous bone scaffolds. The HA fibers were found out to be very interesting from a biological standpoint, but the fragility of the fibers limits their usability as such and therefore methods to incorporate bioceramic fibers into more rigid support structures should be developed. The method to prepare nanocrystalline HA by the conversion of CaCO3 proved to be highly conformal as evidenced by its ability to preserve the original shape of the ALD films and electrospun fibers. NTWE and EB were shown to be capable of producing high quality nanofibers and to provide a viable upscaling route to conventional electrospinning. In contrast, the quality of the SBS fibers needs improvement. Further work would be required to conclude if EB and NTWE are upscalable to industrial scale production levels.
  • Luoma, Samrit (Helsingin yliopisto, 2016)
    This thesis clarifies the potential impacts of climate change and sea-level rise under future climate scenarios on groundwater recharge and surface leakage, and consequently on the groundwater vulnerability of a shallow, unconfined, low-lying coastal sedimentary aquifer in southern Finland. The study utilised multiple approaches, including field investigations, well monitoring, three-dimensional (3D) geological modelling, 3D groundwater flow modelling, multivariate statistical approaches (principal component analysis (PCA) and hierarchical cluster analysis (HCA)), the stable isotopes δ2H and δ18O, conventional hydrogeochemistry and groundwater intrinsic vulnerability assessment methods. The UZF1 model was coupled with the 3D groundwater MODFLOW model to simulate flow from the unsaturated zone through the aquifer. The well-calibrated groundwater flow model was used to simulate and predict the potential impacts of climate change on groundwater recharge under future climate and sea-level rise scenarios. The results indicate changes in the groundwater recharge patterns during the years 2071 2100, with recharge occurring earlier in winter and early spring. Because the aquifer is located in a cold snow-dominated region, the seasonal impacts of climate change on groundwater recharge were more significant, with land surface overflow resulting in flooding during the winter and early spring and drought during the summer. Rising sea levels would cause some parts of the aquifer to be submerged under the sea, compromising groundwater quality due to the intrusion of seawater. This, together with increased groundwater recharge, would raise the groundwater level and consequently contribute to more surface leakage. The groundwater geochemistry of the coastal aquifer in Hanko is very similar to that of inland shallow aquifers generally in Finland, where the groundwater is mainly of the Ca HCO3 type, with low dissolved element concentrations, low pH and alkalinity, and low Ca and Mg concentrations due to rapid percolation or the short residence time. The stable isotopes δ2H and δ18O clearly suggest that the Hanko aquifer recharges directly from meteoric water (snowmelt and rainfall), with minor or insignificant contributions from the Baltic Sea and surface water. However, the geochemistry of the groundwater suggests sulphate reduction in the mixed zone between freshwater and seawater, indicating that local seawater intrusion may temporarily take place, although the contribution of seawater was found to be very low. Further inland, the influence of surface water could be observed from higher levels of KMnO4 consumption in wells near the lake above the aquifer. The findings also demonstrated that the use of stable isotopes δ2H and δ18O alone to identify seawater aquifer interaction is not sufficient to determine the rate of water exchange. The high temporal variation in groundwater chemistry directly corresponded to groundwater recharge. With an increase in groundwater recharge, KMnO4 consumption, EC, alkalinity and Ca concentrations also increased in most wells, while Fe, Al, Mn and SO4 were occasionally increased during the spring after snowmelt under specific geological conditions. Based on the future climate scenarios, precipitation in the Hanko area is expected to increase and the Baltic Sea level to rise. This could cause increased recharge of the aquifer from surface water, but also some seawater intrusion due to the sea-level rise and storm surges, as well as increased groundwater abstraction. An increase in the concentrations of some dissolved elements and changes in groundwater geochemistry along the coastline can be expected in the future. Thus, in coastal aquifers with low hydraulic gradients, the hydrogeochemistry should be used to confirm the intrusion of seawater. The PCA and HCA multivariate statistical approaches are useful tools to extract the main components that are able to identify the vulnerable areas of the aquifer impacted by natural or human activities, either on regional or site-specific scales. The integration of PCA and HCA with conventional classification of groundwater types, as well as with the hydrogeochemical data, provided an understanding of the complex groundwater flow systems, supporting aquifer vulnerability assessment and groundwater management in the future. The degree of groundwater vulnerability in the Hanko aquifer has been greatly impacted by seasonal variations in groundwater recharge during the year, and will also vary depending on climate change variability in the long term. The potential for high groundwater vulnerability to contamination from sources on the ground surface occurs during the period with a high groundwater recharge rate after snowmelt, while high vulnerability to seawater intrusion could occur when there is a low groundwater recharge rate in the dry season. This thesis study highlighted the importance of the integration of groundwater vulnerability assessment methods for shallow, unconfined, low-lying coastal aquifers from a comparison of three intrinsic vulnerability mapping methods: the AVI, a modified version of SINTACS and the GALDIT method. The modified SINTACS could be used as a guideline for groundwater vulnerability assessment of glacial and deglacial deposits in inland aquifers, and in combination with GALDIT, it could provide a useful tool for assessing groundwater vulnerability to both contamination from sources on the ground surface and to seawater intrusion for shallow, unconfined, low-lying coastal aquifers under future climate change.
  • Sukselainen, Leena (Helsingin yliopisto, 2016)
    Pliopithecoidea is an extinct and diverse superfamily of primitive catarrhine primates with no known descendants. They first appear in the fossil record in the late early Miocene China, ca. 18 17 million years ago (Ma). They were widely distributed throughout Eurasia between ca. 17 and 7 Ma and were among the first primates to be discovered and described. Despite their wide distribution, pliopithecoids are rarely found together with the contemporaneous and equally widely distributed hominoid primates. The latest known occurrence of pliopithecoids is also from China where they co-existed with hominoids in the late Miocene ca 6.9 6.2 Ma. Continuing climatic deterioration and dispersal of cercopithecoid primates from Africa may have contributed to their demise. The main objective of this study is to produce new information on pliopithecoids, their environments, as well as on environmental conditions in Eurasia during the Miocene (23 5.3 Ma), with a special focus on the middle Miocene Inner Mongolian locality of Damiao. These goals are approached first by inspecting the differences between pliopithecoid localities and other contemporaneous localities with particular focus on the rare localities of co-occurring pliopithecoid and hominoid primates. To do this we used both traditional ecological diversity analysis as well as direct ecometric method based on hypsodonty in mammalian herbivores. A closer examination of the Inner Mongolian pliopithecoid locality, Damiao, will follow, using small mammal taphonomy, faunal similarity, ecometrics, and stable isotope analyses. The aim is to understand the presence of humid-favouring pliopithecoid primates in central Asia after the middle Miocene climatic optimum (MMCO; ca. 17 15 Ma). The reason this is interesting is because it seems to contradict the general trend of strengthening climatic zonality and increasing aridity from the early Miocene onwards. The results show that pliopithecoids inhabited more humid environments than other contemporary primate groups, suggesting an inability to adapt to changing environmental conditions. The conservative nature of pliopithecoid adaptations seems to have restricted the co-occurrence of pliopithecoids and hominoids, and has been therefore rarely documented. The study also suggests that direct ecometric analysis gives a better separation of the ecological preferences of these primates than do analyses of taxonomically based community structure. The results in Damiao support previous inferences concerning the presence of locally humid environments within the increasingly arid surroundings that characterized Central Asia. Environments within the DM01 locality may have been more humid and possibly more forested and wooded, as suggested by hypsodonty, estimated mean annual precipitation (MAP), local sedimentology and large mammal fossils. We compared our results with the adjacent fossil-rich middle Miocene Tunggur localities. However, the small mammal fauna and isotope data are consistent with a mosaic of forest and grassland environment for all Damiao localities. Based on our results, Tunggur may have been too seasonal or not sufficiently humid for pliopithecoids. This idea is supported by the higher mean hypsodonty and lower predicted MAP estimates, as well as slightly higher δ13C values. We suggest that DM01, the driest known Asian pliopithecoid locality, may have been a more humid refugium within a generally drier regional context. The bone material in Damiao was mainly accumulated by predators and deposited in a fluvial setting. Some reworking by fluvial process took place in DM01 and DM02. DM16 represents the distal part of the floodplain; DM01 portrays a channel-fill; and DM02 is a result of an episodic flood discharge to the floodplain. We also show that systematic excavation for small mammals is possible, and allows for the reduction of some of the damage collecting always causes.