Matemaattis-luonnontieteellinen tiedekunta


Recent Submissions

  • Niskanen, Annina (Helsingin yliopisto, 2018)
    Arctic-alpine regions are facing notable climatic changes. Improved understanding is needed of how these changes cascade into species distributions and what they might mean for the Arctic-alpine realm. These high-latitudes are expected to be susceptible to change. This vulnerability highlights the importance of identifying drivers of Arctic-alpine species and the landscape features that support their persistence. This thesis examines the determinants of present-day refugia; investigates drivers of plant richness and how projected hotspots coincide with conservation areas; forecasts refugia for species persistence and their connection to topo-geological features; and predicts forthcoming changes in species distributions and sensitivity, and whether these are affected by biogeographic history. Multiple statistical modelling approaches were combined with extensive data on species occurrences and environmental drivers. Models were built for refugia, vascular plant species, and various aspects of species richness. Changes in responses were projected across climate scenarios within Fennoscandia. The pronounced climate-dependency of high-latitude species and refugia suggests climate change to have substantial impact on the region’s flora. However, incorporation of topo-geological drivers improved models and forecasts of refugia. Refugia may be especially important for species persistence under severe climate change, particularly for rare or threatened species. Diversity hotspots exhibited low congruence due to variance in key drivers: total species richness prospers in warmer conditions; hotspots of range-restricted species occur near the cooler Northern Scandes. Protected areas in northern Fennoscandia offer limited coverage for these culminations of biodiversity. The climate change sensitivity of high-latitude flora depends not only on predicted warming, but on regional geography and species biogeographic history. Contrary to global estimates these findings do not predict poleward range center shifts. Northern Arctic species are more likely to experience southward contractions and become endangered through range loss. Northern Scandes are projected to be particularly susceptible. The results draw attention to high elevations such as the Southern Scandes for the persistence of cold-adapted flora, though suitable habitat may not persist for all species. Results demonstrate the potential significance – and some unexpected effects – of climate change in the Arctic-alpine realm. Findings of substantial, non-poleward range contractions and decreases in species richness may be counterbalanced by the refugial safeguarding of Arctic-alpine vegetation. Importantly, forecasts are affected by landscape-scale factors and biogeographical history, opening interesting avenues for future research. This study demonstrates the critical role of high-quality data sampled at resolutions reflecting significant environmental gradients for developing useful models of species distributions and richness. The methods used allowed refugia and diversity to be successfully modelled. This provides further insight into current and future conditions for high-latitude flora and highlights the importance of underlying ecological knowledge. From an applied point of view, results emphasize the significance topo-geologically defined areas for biodiversity. The potential locations and environmental parameters of refugia and ecosystem changes herein can inform conservation strategies within the Arctic-alpine realm and beyond.
  • Safi, Elnaz (Helsingin yliopisto, 2018)
    With increasing demand for the energy in last decades, replacing scarce fossil fuels with new energy resources is inevitable. Currently, there is no clear alternative to the old and regular energy production methods for a clean future. However, nuclear fusion power may offer practical, power-plant-scale energy production with an unlimited fuel supply. A major challenge to overcome in the fusion reaction is to produce more energy than it consumes under extremely harsh operating conditions. In the last few decades, a wide range of studies have been carried out to investigate fusion performance and fusion reactor designs. ITER will be the first experimental tokamak-like nuclear fusion reactor to produce net energy, based on deuterium–tritium plasma. Due to the ITER design and operation requirements, extreme conditions are expected for plasma-facing components, such as very large thermal loads, temperature and particle fluxes. Therefore, selecting appropriate materials for different components of the device is critical and highly demanding. The main candidates for the first wall materials in future fusion reactor, ITER are tungsten for the divertor plates and beryllium for the main wall. Moreover, special low-activation ferritic steels are developed for being used as structural materials in blanket modules. In addition, various steels containing of iron and carbon are being considered for the main wall of the DEMO. The plasma cannot be confined infinitely and to control the contact between the escaped plasma and the wall, the area of interaction is restricted to divertor or limiter structures, leading to erosion of them. This phenomenon can become a show stopper by limiting the lifetime of wall materials. Therefore, characterizing the erosion behavior and morphology changes of these components and understanding the underlying mechanism are essential toward predicting and ultimately controlling the adverse effects of plasma surface interactions. Experiments in the different tokamaks and linear plasma devices, as well as those using ion beams are dedicated to study plasma surface interactions. However, experiments show a complex outcome and provide insufficient information to understand the underlying mechanism if the physics is poorly understood. In addition to experiments, computer simulations to study plasma surface interaction have also contributed to a better understanding of future fusion reactors and characterization of this mechanism in a wide range of time and length scales. In this dissertation, the plasma wall interactions such as erosion and ion reflection for the firstwall materials of future fusion reactors have been studied by different computational methods. The interactions of different materials with plasma and impurity particles were modelled. The work was mainly based on molecular dynamics (MD) simulations and an Object Kinetic Monte Carlo (OKMC) algorithm to extend earlier results to a longer time and length scales and thereby enables direct comparison with performed experiments. First, deuterium irradiation on pure Fe, Fe with 1% C impurity and Fe 3 C, under different irradiation energies and substrate temperatures was modelled. Furthermore, a MD study to investigate the effect of plasma impurities D, Ar and Ne on the erosion and surface structure of W and Be was carried out for different fractions of Ar and Ne. Furthermore, the effect of reactor-relevant parameters on Be erosion behaviour and surface changes have been investigated using MD and subsequently a multi-scale approach (KMC- MD).
  • Pajunen, Virpi (Helsingin yliopisto, 2018)
    The ongoing climate change and increasing anthropogenic pressure threaten the biodiversity on Earth. Elevated temperatures, changes in precipitation and intensive land use alter ecosystems and such changes are prone to escalate in the northern regions, especially in freshwater ecosystems. Information about the effects of climate on the distributional patterns of diverse aquatic micro-organisms has yet largely been lacking. This is a drawback as microbial species in freshwaters play crucial roles in ecosystem functioning as well as in environmental monitoring. Thus, it is necessary to disentangle the main drivers of microbial species distributions in order to predict the responses of freshwater communities to future environmental change and to ensure the accurate determination of the ecological status of ecosystems. This doctoral thesis aims to investigate the relative roles of climate, catchment properties and local environmental factors in the occurrence of the important freshwater micro-organisms both at species and community levels. This study, conducted at a regional scale (c. 1000 km), concentrates on unicellular stream diatoms, which are widely used in biomonitoring. The results showed that climatic factors are important drivers of stream diatom distributions and their influence may even outcompete the effects of local environmental variables. However, the relative importance of the factors governing diatom distributions varied along the anthropogenic land use gradient and among species. Climate was the main driver of species distributions in pristine environments, whereas local environment was more important in human impacted streams. Diatom assemblages were also found to be reliable predictors of both climatic and local environmental factors indicating their robustness as environmental proxies and bioindicators. This thesis contributes to the spatial research of aquatic micro-organisms as it brings a novel evidence of the biogeographical patterns of microbial species. This study revealed that climate, one of the fundamental drivers of species distributions on Earth, governs also the occurrences and abundances of stream diatoms even at regional scales. However, it is important to acknowledge that the effects of the most essential factors influencing diatom species may be context dependent and vary along the anthropogenic land use gradient. The ongoing climatic and subsequent environmental change may further complicate the species responses towards environmental factors. From an applied perspective, this study confirmed the reliability of stream diatom assemblages as bioindicators. However, diatom responses towards novel environmental conditions need to be reevaluated to assure their accuracy also in the future.
  • Suomivuori, Carl-Mikael (Helsingin yliopisto, 2018)
    The efficient absorption and utilization of sunlight is one of the most fundamental processes of life, as it is required both for photosynthesis and for visual perception. Biological light capture occurs through light-sensitive molecules called chromophores, which are embedded in complex protein environments that greatly affect both the wavelength of the absorbed light and the subsequent light-triggered activation process. Despite extensive experimental and theoretical studies of photobiological systems, the molecular mechanisms by which proteins affect the light absorption of biological chromophores remain unclear. In this doctoral thesis, we combine large-scale correlated quantum chemical calculations, hybrid quantum mechanics/molecular mechanics (QM/MM) methods, and extensive classical molecular dynamics (MD) simulations to address the light capture in photobiological systems. We employ these computational approaches to study the green fluorescent protein (GFP), photosynthetic reaction centers, as well as both artificial and natural retinylidene proteins. We show how correlated second-order ab initio calculations can be made feasible for large quantum chemical models by employing the reduced virtual space (RVS) and Laplace-transformed scaled opposite-spin (LT-SOS) approximations. Our results uncover intrinsic differences in the excited-state properties of different photosynthetic reaction centers and help determine the color-tuning mechanism of retinal in engineered rhodopsin mimics. Finally, as a result of this work, we propose a mechanism for the ion translocation in the newly discovered light-driven Na+ pump, Krokinobacter eikastus rhodopsin 2 (KR2). Elucidating the fundamental physical and chemical principles behind biological light capture is essential for developing, e.g., novel biomarkers, optogenetic tools, and biomimetic catalysts for energy conversion.
  • Schütt, Jorina Marlena (2018)
    Subduction zones play an important role in the dynamics of the Earth. At plate margins, where one tectonic plate subsides underneath a second one, mountain ranges are built, earthquakes experienced and volcanic activity observed. The subduction zone of South America, where the Nazca Plate slides underneath the South American Plate, extends for roughly 7000 km along the plate margin. Ongoing since at least the Cretaceous this subduction zone is a laboratory for tectonic systems. This study focuses on how the geometry and relative motion of the two converging plates affects dynamics in the overriding plate utilizing 3D numerical mechanical and thermo-mechanical models. Along the South American subduction zone the obliquity angle, subduction dip angle and strength of the continental crust vary. All these factors influence the dynamics and deformation of the continental crust and affect – especially in oblique subduction systems – how oblique convergence is partitioned onto various fault systems in the overriding plate. In order to investigate which of these factors are most important, this study compares results of lithospheric-scale 3D numerical geodynamic experiments from two regions in the north-central Andes: the Northern Volcanic Zone (NVZ; 5°N - 3°S) and adjacent Peruvian Flat Slab Segment (PFSS; 3°S -14°S). These regions exhibit a range of different configurations of the abovementioned subduction zone characteristics (from areas of extensive volcanism, large obliquity angle and well-defined sliver movement to areas lacking volcanic activity as well as significant strain partitioning) and are therefore well suited as study areas. Results from a range of experiments show that the obliquity angle has, as expected, the largest effect on initiation of strain partitioning, but development of sliver movement parallel to the margin is clearly enhanced by the presence of a continental weakness. Experiments combining different characteristics show that the subduction dip angle has the smallest impact on sliver formation. Purely mechanical models are despite their simplicity a good suited tool for investigations of subduction zone dynamics and in very good agreement with observations in nature in the particular study areas of this work as well as global subduction zones. In order to step closer to nature, the reference models (representing the NVZ and PFSS) were revisited with fully coupled thermo-mechanical experiments. The sliver movement observed in the thermo-mechanical models agrees well with their purely mechanical counterpart. While this is the case, the thermo-mechanical experiments do expose the boundary between successful (NVZ) and partly failing (PFSS) incorporation of temperature dependence into mechanical models. With this they provide a good starting point for further refinement and development of temperature dependent experiments.
  • Hohenthal, Johanna (Helsingin yliopisto, 2018)
    In many developing countries, formal natural resource management is still largely based on top-down approaches that rely on professional ecological knowledge and bureaucratic procedures. Despite general support for community participation in the context of decentralised governance, perspectives of local people are often neglected in management planning and decision-making. At the same time, local people are considered responsible for environmental degradation, while historical political, economic and other structural changes, which have led to unsustainable land and water uses, are overlooked. This dissertation focuses on examining the challenges and possibilities of enhancing community participation and the role of local ecological knowledge in environmental management through a case study from the Taita Hills, Kenya. Political ecology provides the overall framework for the study and both theoretical and ethical guidance are drawn from postcolonial and decolonial thinking. The dissertation consists of one review and four case study articles that are tied together by a “pathway” towards decolonizing environmental governance and building of symmetric dialogues between local people and state authorities. The material for the case studies was largely collected through a multi-method participatory mapping process in 2013-2014. The process is methodologically important because it highlights the significance of the historical perspective for understanding socio-environmental problems and respects local ways of knowing and thus provides the possibility to move towards decolonizing knowledge production. This study shows how the causes of increasing vulnerability and decreasing resilience to water scarcity and droughts can be traced back to changes in land use policies, the impacts of the neoliberalization of environmental governance, and ultimately, the subalternization of local people and their ecological knowledges. Furthermore, the dissertation locates the roots of the asymmetric environmental dialogues between local people and management authorities to the diverging framings of the environmental problems. Prioritization of the state’s economic interests in local environmental negotiations, instead of local perspectives and historical injustices, reproduces the coloniality of power. To overcome this vicious circle, societal learning and transformation are needed.
  • Peltonen, Ella (Helsingin yliopisto, 2018)
    Mobile devices, especially smartphones, are nowadays an essential part of everyday life. They are used worldwide and across all the demographic groups - they can be utilized for multiple functionalities, including but not limited to communications, game playing, social interactions, maps and navigation, leisure, work, and education. With a large on-device sensor base, mobile devices provide a rich source of data. Understanding how these devices are used help us also to increase the knowledge of people's everyday habits, needs, and rituals. Data collection and analysis can thus be utilized in different recommendation and feedback systems that further increase usage experience of the smart devices. Crowdsensed computing describes a paradigm where multiple autonomous devices are used together to collect large-scale data. In the case of smartphones, this kind of data can include running and installed applications, different system settings, such as network connection and screen brightness, and various subsystem variables, such as CPU and memory usage. In addition to the autonomous data collection, user questionnaires can be used to provide a wider view to the user community. To understand smartphone usage as a whole, different procedures are needed for cleaning missing and misleading values and preprocessing information from various sets of variables. Analyzing large-scale data sets - rising in size to terabytes - requires understanding of different Big Data management tools, distributed computing environments, and efficient algorithms to perform suitable data analysis and machine learning tasks. Together, these procedures and methodologies aim to provide actionable feedback, such as recommendations and visualizations, for the benefit of smartphone users, researchers, and application development. This thesis provides an approach to a large-scale crowdsensed mobile analytics. First, this thesis describes procedures for cleaning and preprocessing mobile data collected from real-life conditions, such as current system settings and running applications. It shows how interdependencies between different data items are important to consider when analyzing the smartphone system state as a whole. Second, this thesis provides suitable distributed machine learning and statistical analysis methods for analyzing large-scale mobile data. The algorithms, such as the decision tree-based classification and recommendation system, and information analysis methods presented in this thesis, are implemented in the distributed cloud-computing environment Apache Spark. Third, this thesis provides approaches to generate actionable feedback, such as energy consumption and application recommendations, which can be utilized in the mobile devices themselves or when understanding large crowds of smartphone users. The application areas especially covered in this thesis are smartphone energy consumption analysis in the case of system settings and subsystem variables, trend-based application recommendation system, and analysis of demographic, geographic, and cultural factors in smartphone usage.
  • Barral, Oswald (Helsingin yliopisto, 2018)
    Implicit interaction refers to human-computer interaction techniques that do not require active engagement from the users. Instead, the user is passively monitored while performing a computer task, and the data gathered is used to infer implicit measures as inputs to the system. Among the multiple applications for implicit interaction, collecting user feedback on information content is one that has increasingly been investigated. As the amount of available information increases, traditional methods that rely on the users' explicit input become less feasible. As measurement devices become less intrusive, physiological signals arise as a valid approach for generating implicit measures when users interact with information. These signals have mostly been investigated in response to audio-visual content, while it is still unclear how to use physiological signals for implicit interaction with textual information. This dissertation contributes to the body of knowledge by studying physiological signals for implicit interaction with textual information. The research targets three main research areas: a) physiology for implicit relevance measures, b) physiology for implicit affect measures, and c) physiology for real-time implicit interaction. Together, these provide understanding not only on what type of implicit measures can be extracted from physiological signals from users interacting with textual information, but also on how these can be used in real time as part of fully integrated interactive information systems. The first research area targets perceived relevance, as the most noteworthy underlying property regarding the user interaction with information items. Two experimental studies are presented that evaluate the potential for brain activity, electrodermal activity, and facial muscle activity as candidate measures to infer relevance from textual information. The second research area targets affective reactions of the users. The thesis presents two experimental studies that target brain activity, electrodermal activity, and cardiovascular activity to indicate users' affective responses to textual information. The third research area focuses on demonstrating how these measures can be used in a closed interactive loop. The dissertation reports on two systems that use physiological signals to generate implicit measures that capture the user's responses to textual information. The systems demonstrate real-time generation of implicit physiological measures, as well as information recommendation on the basis of implicit physiological measures. This thesis advances the understanding of how physiological signals can be implemented for implicit interaction in information systems. The work calls for researchers and practitioners to consider the use of physiological signals as implicit inputs for improved information delivery and personalization.
  • Jyrkänkallio-Mikkola, Jenny (Helsingin yliopisto, 2018)
    Freshwaters harbour disproportionally high biodiversity in relation to their area. Yet, they are among the most threatened ecosystems on Earth due to the increasing anthropogenic pressures. The ongoing climate change and Holocene extinctions give rise to an increasing need for conservation efforts in order to avoid future species losses. Successful conservation attempts require a comprehensive understanding how species and communities are distributed in space and time. There are notable gaps in the knowledge of diversity gradients of hyperdiverse microbes and invertebrates, and this knowledge gap is more pronounced in the tropics. This thesis seeks to 1) investigate the effects of local environmental, catchment characteristics, spatial and climatic factors on stream communities across sites and catchments; 2) examine benthic diatom diversity patterns and the underlying factors within and among streams and stream orders; 3) examine the effect of environmental heterogeneity on benthic diatom beta diversity and; 4) compare the diversity patterns of stream diatoms and insects between boreal and tropical regions. To accomplish these aims, microbial and insect communities were collected from boreal and tropical regions and the underlying causes of community spatial variation were investigated using advanced statistical methods. The thesis demonstrated that stream communities are driven by a range of factors acting on multiple spatial scales. Water chemistry, stream physical variables, biotic interactions, land use, spatial and climatic factors contributed to the variation in stream community composition and taxonomic richness. Diatom community composition exhibited significant within- and among-stream variation at intermediate spatial scales, which has relevance for biomonitoring using diatoms. Headwater streams exhibited higher beta diversity and harboured regionally unique diatom communities, which encourages the conservation of headwater streams. It was further demonstrated that environmental heterogeneity promotes diatom beta diversity, which emphasizes the role of habitat heterogeneity in sustaining diverse communities. Somewhat surprisingly, diatom species richness was not higher in the tropics than in the boreal study region, and a notable number of diatom species were found from both regions. This implies that diatoms may not follow the traditional global latitudinal diversity gradient and further suggests that some diatom species exhibit global distributions. Insect genus richness was slightly higher in the tropics than in the boreal study region, whereas insect abundance was significantly higher in the boreal than the tropical region. The large within-region variation in insect genus richness and abundance may be more strongly driven by factors operating at regional scale than by the region itself, further suggesting that streams exhibit uniqueness and do not fit well into predefined categories based purely on latitude. In summary, this thesis increases knowledge of the underlying variables affecting stream community variation. Further, biomonitoring and conservational efforts may benefit from the identified factors contributing to regional stream diversity. Finally, this thesis increases knowledge and understanding of the similarities and differences of stream communities across regions.
  • Gong, Yongmei (Helsingin yliopisto, 2018)
    Ice shelves and ice caps constitute a great proportion of the glacial ice mass that covers 10% of the global land surface and is vulnerable to climate change. Large scale ice flow models are widely used to investigate the mechanisms behind the observed physical processes and predict their future stability and variability under climate change. This thesis aims at providing general remarks on the application of ice flow models in studying glaciological problems through investigating the evolution of an Antarctic ice shelf under climate change and the mechanisms of fast ice flowing events (surges) in an Arctic ice cap. In addition discussions of the equivalence of two significantly different expressions for the rate factor in Glen’s flow are also provided. Off-line coupling between the Lambert Glacier-Amery Ice Shelf (LG-AIS) drainage system, East Antarctica, and the climate system by employing a hierarchy of models from general circulation models, through high resolution regional atmospheric and oceanic models, to a vertically integrated ice flow model has been carried out. The adaptive mesh refinement technique is specifically implemented for resolving the problem concerning grounding line migration. Sensitivity tests investigating the importance of various parameters and boundary conditions are carried out in ice flow models with different approximations for Austfonna Ice-cap, Svalbard to investigate the surge event in one of its basins, Basin 3. Inverse modelling of basal friction coefficient is specifically implemented. A continuum to discrete multi-model approach is implemented for simulations of Basin 3. LG-AIS drainage system will be rather stable in the face of future warming over 21st and 22nd centuries. Although the ice shelf thins in most of the simulations there is little grounding line retreat. The change of ice thickness and velocity in the ice shelf is mainly influenced by the basal melt distribution. And the Lambert, Fisher and Mellor glaciers are most sensitive to thinning of the ice shelf south of Clemence Massif. The sea level rise contribution of LG-AIS is modest as the increased accumulation computed by the atmosphere models outweighs ice stream acceleration. Using a temporally fixed basal friction field obtained through inverse modelling is insufficient to simulate the future changes of the fast flowing surging glacier in Basin 3. And the evolution of basal friction patterns, and in turn basal processes are among the most important factors during the surge in Basin 3. A system of processes and feedback involving till deformation and basal hydrology is more likely to explain both the seasonal accelerations and the ongoing inter-annual speed-up more than a hard-bed mechanism. The continuum to discrete multi-model approach provides the possible locations of the crevasses that can potentially cut through the full length of the ice and deliver surface melt water down to the bed. The calculated basal water flow paths according to hydraulic potential indicate that the summer speed up events and the initiation of the acceleration in the southern part of the basin can be explained by either a direct enhancement to the ice flow through basal lubrication or a lagged-in-time mechanism through the outflow of accumulated water in the over-deepening area. Keywords: ice flow modelling, climate change, sea level rise, future projection, basal sliding, basal hydrology, surface melt, surging glacier, Lambert Glacier-Amery Ice Shelf, Austfonna Ice-cap, Antarctic, Svalbard
  • Shang, Yuan (Helsingin yliopisto, 2018)
    Red Clay and overlying loess-palaeosol sequences are typical for the area in northern China that is known as the Chinese Loess Plateau (CLP). These primarily aeolian sediments provide one of the best terrestrial archives of Neogene-Quaternary climate change, and their formation has been linked to the uplift of the Tibetan Plateau, the progressive aridification of East Asia and the onset of and changes in the East Asian monsoon. In the present study, the sediment provenance was reconstructed using a combination of analytical techniques that allowed better understanding of the (long-term) shifts in sediment delivery in response to changes in the climate and tectonic evolution. Zircon U–Pb age spectral and backtrace trajectory modelling of three well-known Red Clay sequences distributed across the CLP revealed spatiotemporal variations in the provenance of late Miocene-Pliocene Red Clay. The results indicate that the Red Clay in the southern and western CLP was mainly derived from the Northern Tibetan Plateau (NTP) and the Taklimakan Desert. In contrast, Red Clay in the northeastern CLP displays a zircon U-Pb age signature of the broad area of the Central Asian Orogenic Belt. In addition, the northeastern Red Clay shows increased contributions from the west around 3.6 Ma, possibly suggesting an intensified westerly wind strength and/or aridity of the NTP and Taklimakan Desert arising from the uplift of the NTP and Tianshan Mountains in the Pliocene. This could also be caused by the onset of enhanced Yellow River drainage in response to the increased NTP denudation since 3.6 Ma. To further investigate the role of the Yellow River in supplying dust to the Quaternary loess deposits, the sedimentology and source signal of the unique loess-palaeosol sequence of the Mangshan Loess Plateau (MLP) along the lower reach of the Yellow River was investigated by end-member modelling of the loess grain-size records and single-grain zircon U-Pb dating. The results suggest that the Yellow River floodplain north of the MLP has served as a major dust source at least since 900 ka. The sudden change in sedimentology (accumulation rate, grain-size distribution) of the Mangshan sequence above palaeosol unit S2 may have been initiated by a combination of tectonic movements in the Weihe Basin and in the Yellow River floodplain north of the MLP around 240 ka. Subsequent rapid fluvial incision in the northern part of the Weihe Basin resulted in increased sediment flux being transported to the lower reach of the Yellow River. Tectonic movements in the floodplain north of the MLP would have caused a southward migration of the Yellow River course, explaining the formation of an impressive scarp and the more proximal location of the sediment source. In addition to provenance analysis, grain size and shape characteristics obtained by dynamic image analysis (DIA) were used to fingerprint the transport processes of silt particles in a series of Quaternary loess-palaeosol sequences. The results revealed a decrease in the aspect ratio of the particles as a function of increasing grain size, thus indicating that systematic shape sorting occurred during the aeolian transport of the silt particles. A similar particle-shape sorting trend has also been found in a series of Red Clay sequences, confirming that the Red Clay deposits are predominantly of aeolian origin. This study indicates that DIA of grain size and shape characteristics can be an additional powerful tool for fingerprinting trends in grain size and shape sorting, determining the dominant mode of transport, and reconstructing the transportation pathways of silt-sized aeolian sediments. The final part of this thesis research comprised a pilot study on the use of the trace-element composition of quartz as a provenance tool to constrain the source area of the late Neogene and Quaternary dust deposits in northern China. It revealed that quartz in the Mangshan loess deposits is largely derived from the Qaidam Basin of the NTP. The likely dust contribution from the Taklimakan Desert to the Red Clay deposits in Baode is also reflected in the trace element content of quartz. These results are comparable with the source signal obtained from the zircon U-Pb age spectra, suggesting that the trace element composition of quartz could be applied as an alternative tool to other single-grain provenance analytical approaches to track the dust source and dust pathways of the aeolian sediments.
  • Nelimarkka, Matti (Helsingin yliopisto, 2018)
    There is a division among computer-supported collaboration tools by location (collocated/ distributed) and by time (synchronous/asynchronous). Collocated synchronous tools were once given focus in research through studies of group support systems. Today, ubiquitous computing has led to collocated synchronous computing becoming a part of day-to-day life. The practices involved take place in hybrid space – a mixture of face-to-face and computer-mediated communication. This very real, concrete phenomenon has been subject to study in the human-computer interaction domain; however, theories examining social interaction in the hybrid space, or hybrid interaction, are rare. Such theories may help to advance the design and utilization of tools for hybrid interaction. Aimed at helping practitioners understand and benefit from hybrid interaction, a study of one form of it was undertaken, with the emphasis on cases wherein the event is organized as a performance and there are spectators and performers. Hence, the focus is on performative hybrid interaction: hybrid interaction that is used as part of a performance. The work builds on 14 instances of hybrid interaction examined through mixed-methods approaches. The following observations about social practices were made on the basis of the empirical research: (i) Hybrid interaction has social rules that govern how interaction takes place. In this respect, hybrid interaction is like any social interaction. However, the social rules of hybrid interaction emerge from the rules of both computer-mediated and face-to-face interaction. These two communication channels are interlinked and, therefore, influence one another. (ii) In performer-oriented settings, it is important to establish social rules that support the performance. Performative hybrid interaction benefits from active guidance by performers. This active guidance establishes the social rules and communicates them to spectators. Performers establish these rules in several ways, both onstage and offstage. Yet the technical systems employed do not scaffold and support the active guidance. (iii) The choices surrounding social rules are normative decisions. Therefore, frameworks that account for and reflect these decisions can be helpful for designers and researchers. Frameworks of this nature might be adapted, for example, from political science. They benefit research and design in two ways. Firstly, they often provide a set of validated empirical methods that make the research more solid. Secondly, they support the design of systems: they justify the design goals and provide a backdrop against which the design ideas evolve. Discussion proceeding from these findings considers how to improve practices of performative hybrid interaction. The thesis project investigated the importance of accounting for these social practices. Also, I propose further tools for supporting these social practices, such as the script. Furthermore, the thesis contributes to the use of social theories for human-computer interaction, with a synthesis of elements from several fields of research: political science, performance studies, event studies, and sociology. This combination offers insights related to the difficulties and potential problems in performative hybrid interaction. It also provides insight into the role of normative decisions that ought to inform designers and researchers working on performative hybrid interaction.
  • Hitruhin, Lauri (Helsingin yliopisto, 2018)
    The thesis” On multifractal spectra of mappings of finite distortion” consist of introductory part and four articles. These articles revolve around stretching and rotational properties of mappings of finite distortion both in pointwise and global situations. In the second and third articles the sharp bounds for pointwise rotation of homeomorphisms with exponentially integrable distortion and homeomorphisms with integrable distortion have been established. The sharpness of these bounds is verified by constructing examples using nested annuli. The proofs for optimal bounds are based on techniques utilizing the modulus of path families. The idea is to find suitable path families and use inequality for moduli to find the correct bounds for rotation. This approach also highlights the correlation between stretching and rotation. Moreover, it can also be used for studying optimal pointwise stretching, where we can sharpen the previously known bound for homeomorphisms with integrable distortion. The method using modulus of path families differs from the methods used for obtaining the optimal bounds for quasiconformal mappings, which was done by Astala, Iwaniec, Prause and Saksman. In the first and fourth articles the maximal size of sets in which mappings of finite distortion can attain some predefined stretching and rotation is studied. Identifying the maximal size for all suitable combinations of stretching and rotation amounts to finding the multifractal spectra. In the first article the previously known bounds for the multifractal spectra of quasiconformal mappings, established by Astala, Iwaniec, Prause and Saksman, were sharpened to the level of the Hausdorff measures. This was done by constructing examples using non self-similar Cantor like sets. In the fourth article the multifractal spectra was studied for homeomorphisms with integrable distortion. Here the optimal bounds for the spectra were given and examples proving sharpness presented. Moreover, as an application a question by Clop and Herron, regarding compression of the Hausdorff measure for homeomorphisms of integrable distortion, was answered. Methods used in the proof for the spectra resemble those used in the pointwise case, but the choice of a suitable path family is more involved in this situation.
  • Gregow, Erik (Erweko, 2018)
    Observations have been and are an important part of today's meteorological developments. Surface observations are very useful as they are, providing weather information for a point location. Though they do not give much information, if any, on what happens between the stations across a larger area. With models one can create an analysis of the meteorological situation, i.e. calculate and estimate what happens between these fixed observation points. Remote-sensing data, such as radar and satellite, are being processed and the output is given over a domain as an analysed product of their measurements. For example, radar gives a plot of where the rain is located, i.e. an analysis of the current precipitation. With a series of radar images, a human (subjectively) or a computer (objectively) can process this information to estimate where the rain will move and be located within the next few minutes (even hours), i.e. a short forecast also called "nowcast". This applies to some extent also for other observations, such as satellite data (cloud propagation). But for most quantities (such as temperature, wind, etc) it is significantly harder to make such a nowcast, since these are influenced by many other factors and there is no linear development of them. Therefore, there are forecast models that solve physical and dynamic equations, so that one can estimate the future weather for the coming hours and days. A prerequisite for generating a forecast of high quality is to capture the initial weather conditions as best as possible. This is done using observations and they are introduced into the forecast model through different techniques, where the model creates its own analysis as the initial step. There remain problems since forecast models often are affected by physical disagreements, as the dynamic conditions are not in balance. This results in the model having a spin-up effect, where the meteorological quantities are not yet in balance with each other and the resulting weather conditions are not always reliable during the first hours. Hence, a lot of research is spent on how to reduce this spin-up effect and on the use of nowcast models, in order to deliver the best model results for the first few hours of the forecast period. In this dissertation, the research work has been to improve the meteorological analysis, algorithms and functionality, using the Local Analysis and Prediction System (LAPS) model. Different kinds of observations were used and their interdependencies have been studied, in order to combine and merge information from various instruments. Primarily focus has been to improve the estimation of precipitation accumulation and meteorological quantities that affect wind energy. The LAPS developments have been used for several end-users and nowcasting applications, and experimentally as initial conditions for forecast modelling. The studies have been concentrated on Finland and nearby sea areas, with the available datasets for this domain. By combining surface-station measurements, radar and lightning information, one can improve the precipitation-amount estimations. The use of lightning data further improves the estimates and gives the advantage of having additional data outside radar coverage, which can potentially be very useful for example over sea areas. In addition, the improved LAPS analyses (cloud-related quantities) and a newly developed model (LOWICE), calculating the electricity production during wintertime (e.g. icing which reduces efficiency), have shown good results.
  • Tsuruta, Aki (Helsingin yliopisto, 2017)
    Ensemble Kalman filter (EnKF) is a useful Bayesian inverse modelling method to make inference of the states of interest from observations, especially in non-linear systems with a large number of states to be estimated. This thesis presents an application of EnKF in estimation of global and regional methane budgets, where methane fluxes are inferred from atmospheric methane concentration observations. The modelling system here requires a highly non-linear atmospheric transport model to convert the state space on to the observation space, and an optimization in both spatial and temporal dimensions is desired. Methane is an important greenhouse gas, strongly influenced by anthropogenic activities, whose atmospheric concentration increased more than twice since pre-industrial times. Although its source and sink processes have been studied extensively, the mechanisms behind the increase in the 21st century atmospheric methane concentrations are still not fully understood. In this thesis, contributions of anthropogenic and natural sources to the increase in the atmospheric methane concentrations are studied by estimating the global and regional methane fluxes from anthropogenic and biospheric sources for the 21st century using an EnKF based data assimilation system (CarbonTracker Europe-CH4 ; CTE-CH4). The model was evaluated using assimilated in situ atmospheric concentration observations and various non-assimilated observations, and the model sensitivity to several setups and inputs was examined to assess the consistency of the model estimates. The key findings of this thesis include: 1) large enough ensemble size, appropriate prior error covariance, and good observation coverage are important to obtain consistent and reliable estimates, 2) CTE-CH4 was able to identify the locations and sources of the emissions that possibly contribute significantly to the increase in the atmospheric concentrations after 2007 (the Tropical and extra Tropical anthropogenic emissions), 3) Europe was found to have an insignificant or negative influence on the increase in the atmospheric CH4 concentrations in the 21st century, 4) CTE-CH4 was able to produce flux estimates that are generally consistent with various observations, but 5) the estimated fluxes are still sensitive to the number of parameters, atmospheric transport and spatial distribution of the prior fluxes.