Matemaattis-luonnontieteellinen tiedekunta


Recent Submissions

  • Kousa, Päivi (Helsingin yliopisto, 2019)
    Classrooms are becoming more diverse and the number of low achieving students is continuously increasing. About 20% of European 15-year-old-children are not at the required educational levels. There are many reasons for students’ low achievement such as negative attitudes, immigrant or low socio-economic backgrounds, learning difficulties etc. Furthermore, students find that science and especially chemistry is boring, uninteresting, irrelevant and difficult. Nevertheless, low achievement can have critical consequences for the entire society, if students are unable to participate in it as equal citizens, make rational and sustainable decisions or be sufficiently qualified for working life demands. Accordingly, more research is needed, how low achieving students could be supported in diverse classrooms. Science teachers tend have more negative beliefs towards student diversity and teaching practices in diverse classrooms compared to subject teachers. That is crucial, because teachers' beliefs and practices can affect students' achievement. The aim of this thesis is to understand, how science, and especially chemistry teachers could be better supported and prepared for diversity and better student achievement during their entire careers. The main research question is: What is the relationship between student achievement and teachers' beliefs about diversity and science teaching practices for diverse students? In order to answer to the main research question, three subquestions are asked. Firstly, low achieving students' thoughts about chemistry and chemistry teaching practices compared to other students is analyzed. The second question clarifies, how does the STSE-based school-industry collaboration affect to pre-service science teachers' beliefs about their future practices. The third question is about pre- and in-service teachers' beliefs about teaching chemistry in diverse classrooms. This thesis consists of three interconnected studies and one descriptive report (I-IV). Study I describe what is the connection between students' low achievement and most preferred teaching practices compared to other students. Since there was a clear evidence of the fact, that all students in spite of their achievement levels preferred industry visits, it was chosen to be a main topic in study II. In that study, the connection between pre-service teachers' beliefs and STSE-based teaching practices were examined in a context of school-company collaboration and visits. Since pre-service teachers' beliefs were significantly improved after the STSE-based course, the following descriptive report III concentrated on science teacher education and how it could be developed in order to prepare future chemistry teachers for diversity. Furthermore, the last study IV is about the in-service chemistry teachers' beliefs about their work in diverse classrooms. The mixed methods approach which includes survey and case-study is used in order to answer the research questions. Data for the survey was collected from 2949 secondary school students with the help of the Finnish National Board of Education (study I). Secondly, the effects of STSE-based teaching practices were carried out in Finland and Slovenia with 42 pre-service chemistry and science teachers (study II). The presented teaching model for teaching diverse students (report III) was based on German and Finnish chemistry teacher education programs. Furthermore, the beliefs of eight in-service science teachers were examined by case-study (study IV). There is not much national or international research about the topic of this thesis. This thesis presents prominent insights and ideas, how especially low achieving students could be supported by developing science and chemistry teacher education. Accordingly, following suggestions are made: (i) Practices for teaching diverse students have an influence on students' achievement. Therefore, it is beneficial to take students' thoughts into account when activities are planned and implemented. It is worth noticing, that students prefer similar practices in spite of their achievement levels: company visits, using digital implementations and working in groups. (ii) STSE-based teaching practices such as company visits are preferred by diverse students and they also have a positive effect on teachers' beliefs. For that reason, teachers should have regular opportunities to practice those skills in authentic environments. STSE-based teaching material can be also beneficial for diverse students. (iii) In-service teachers do have basic knowledge about diversity, and they use a considerable amount of effort in order to take their students' needs into account. However, they need more support and resources. In conclusion, pre-and in-service teachers' concerns, needs and beliefs should be taken into account, when support for them is planned during their entire career. Teacher support for diversity and better student achievement need both national and international collaboration among teacher educators, pre- and in-service teachers, special education teachers, students, parents and other community members. This has a significant effect on student achievement and the entire society in turn.
  • Manninen, Antti (Helsingin yliopisto, 2019)
    Global and in-situ wind field observations are crucial for predicting weather and climate. Air motions within the atmospheric boundary layer (ABL) affect aerosol-cloud interactions and are essential in forecasting poor air quality episodes. During the last few decades remote sensing instruments, especially Doppler lidars, have been used to monitor the vertical profile of the ABL with high time and height resolution. Such lidars can measure the vertical velocity directly in vertical pointing mode and with a scanning capability also retrieve horizontal winds. From Doppler lidar measurements profiles of turbulent properties, wind shear, and higher order velocity statistics can be calculated – essential in revealing the vertical structure of the ABL. Pulsed Doppler lidar systems using heterodyne detection usually operate in the near-infrared spectral region. They transmit a laser pulse, which scatters from atmospheric particles, and record the backscattered part of the pulse. There are significant limitations in the sensitivity of such lidar systems in locations where aerosol load is low and hence the signal-to-noise ratio (SNR) is low. In theory, sensitivity of a pulsed Doppler lidar system can be improved by averaging the signal and thus increasing the SNR, assuming the noise is Gaussian. If not, the improvement in sensitivity is limited by the noise characteristics. Any bias in SNR is propagated into the velocity uncertainties and further to estimated turbulent properties. This thesis is comprised of research which aimed to fully characterise the noise in the backscatter signal of a pulsed Doppler lidar system, and to develop methods for correcting any bias detected in the noise. The instrument's sensitivity was improved significantly which increased data availability. Method for classifying ABL turbulent mixing was developed by combining several Doppler lidar quantities, which enables estimating the coupling of turbulence to the surface and/or clouds as well as identifying the sources causing turbulent mixing within the ABL. Data processing methods developed for the Doppler lidar system were applied to detect elevated aerosol layers from measurements of another lidar system. The developed methods were collected into a freely available software toolbox with the ultimate aim of generating harmonized Doppler lidar products across European Doppler lidar sites.
  • Anttila, Kati (Helsingin yliopisto, 2019)
    The topic of this dissertation is the seasonal snow surface roughness and albedo. These are studied using optical satellite data and terrestrial laser scanning. The use of remote sensing data requires knowledge on the optical properties of the measured surface. For snow, these properties are affected by surface roughness. In this dissertation, two different methods for measuring snow surface roughness were validated and used in the field. One of them is based on plate photography. It is easy to use in the field and able to study surface features in sub-millimeter scale. The other method is based on mobile laser scanning and is able to produce 3D surface descriptions of large areas. The plate-photography-based method was used in the field to gather 669 profiles of the snow surface. The profiles were analyzed using multiscale parameters. The validation of satellite data requires observations at the surface. This validation data typically consists of pointwise measurements, whereas the satellite data observations cover larger areas. Laser scanning provides data that cover larger areas, thus more in line with the satellite data. This could in the future be used for satellite data validation. The usability of laser scanning data on snow surfaces was improved by studying the incidence angle dependency of the laser scanning intensity data on different snow types. A function for correcting the incidence angle effect on all measured snow types was developed. The backscattering of laser beam on snow surface was found to take place at the very surface for dry snow, and within 1cm depth for wet snow. The final part of this dissertation studies the changes in surface albedo prior to melting and the timing of the melt season in Northern Hemisphere land areas between 40°N and 80°N. The albedo prior to melt had changed significantly in the boreal forest area, but not in the tundra. The direction of change is different in different areas. The melt season takes place at the same time of year for most of the study area, but for Central Siberian Plane the melt season takes place earlier. In Northern Canadian Rocky Mountains and in the area around the borders of Russia, China and Mongolia the melt starts earlier and ends later, thus resulting in longer melt seasons. The changes observed in the pre-melt albedo are related to vegetation, whereas the melt season timing is more related to the climatic parameters. The results of this dissertation can be used in developing remote sensing data and climate models through improved understanding of seasonal snow surface roughness and albedo.
  • Vigonski, Simon (Helsingin yliopisto, 2019)
    Atomistic simulations are a useful way to study nanoscale metal structures. At the nanoscale, the surface to volume ratio of the objects becomes large and surface effects start to play a critically important role. The internal stress near a surface can reach the GPa range and thus its effects should not be neglected when dealing with nanowires and other nanostructures. Similarly, surface diffusion of atoms is important in the manufacturing process and subsequent stability of nanostructures. In the study of vacuum breakdown on Cu surfaces, dislocation activity and surface atom diffusion are thought to play a role in the formation of field enhancing emitters. This work investigates a possible mechanism of nucleation of a nanofeature on metal surfaces under high electric fields in the presence of a near-surface defect, and the stability of Au nanowires with respect to surface diffusion. The simulation methods of molecular dynamics, kinetic Monte Carlo and finite elements are employed. A subsurface Fe precipitate is used as an example of subsurface extended defects, and the nucleation of dislocations in regions of high stress concentration is simulated. A process of forming a protrusion on the surface near the precipitate due to dislocation propagation is shown, as well as the possibility of forming new voids on the precipitate interface. Since atomistic simulations are heavily limited in size and time scales, larger scale simulations are conducted by using finite element modelling of nanoscale material behavior under external loading. However, such modeling requires the development of an accurate model of surface stress. In this work, a surface stress model is implemented into a continuum finite element model to enable faster calculations of more extensive nanoscale systems, as well as to combine the mechanical model with electrical effects in vacuum breakdown research. The internal stresses given by the model are validated in comparison with molecular dynamics simulations and against an analytical model of dislocation emission from a near-surface void. Kinetic Monte Carlo simulation is a suitable tool to simulate diffusion processes. However, setting up KMC simulations requires a parametrization of atomic migration barriers. A consistent parametrization scheme, called the tethering method, is developed in the current work. The tethering method provides a robust automatic process to calculate migration barriers for on-lattice diffusion simulations. It allows the calculation of barriers for unstable processes, while having a minimal effect on stable barriers. The tethering method is used to create a parametrization for Au, which is used to simulate nanowire junction fragmentation. Nanowire junctions break up in a process similar to Rayleigh instability. In conjunction with experiments, it is shown that junctions fragment at a low temperature when nanowires themselves remain whole. Simulations demonstrate that the breakup can be explained by surface energy minimization due to atom diffusion and that the formation of a fragment at the nanowire crossing point is very reliable.
  • Hooda, Rakesh K (Helsingin yliopisto, 2019)
    Atmospheric aerosol particles are linked to visibility reduction and adverse health effects, and radiation balance of the Earth— directly by reflecting and absorbing solar radiation and indirectly by influencing the cloud properties and processes and, possi-bly, by changing the heterogeneous chemistry of reactive gaseous species. Atmospheric aerosols are the most uncertain driver of global climate change. The South‒Asian region has been increasingly recognized as one of the global hotspots of aerosols; and Indo Gangetic Plains (IGP) is one among them with complex geography, heterogeneity in sources and varying atmospheric dynamics. These factors make IGP’s aerosol and pollution very difficult to characterize. So far, long-term regional observations of aerosol properties have been scarce in this region, but argued necessary in order to bring the knowledge of regional and global distribution of aerosols further. In this context, regional studies of aerosol properties their dynamics and atmospheric processes are very important areas of investigation to better estimate the climatic importance of submicron aerosol particles. Moreover regional studies over IGP-Himalayas domain are inevitable to know how trans-Himalayan valleys are acting as conduits for aerosol and pollution transport from the plains to the Himalayas. Therefore, in this thesis we studied these issues by applying basic to state-of-the-art instrumentation in two different envi-ronments, plains—Gual Pahari, and Himalayan foothills— Mukteshwar; to obtain physical and optical properties of submi-cron particles. Additionally, we used meteorological parameters, emissions and process modelling to determine local and region-al scale transport of atmospheric aerosols. The work carried out as part of the thesis infers four main conclusions, 1) Simultaneous long-term measurements at both the environments in Northern India region are useful to establish linkages between sub-urban environment and high altitude sites. One site represents a source region, while another characterize as a receiver site of atmospheric pollutants; 2) A distinct cycle of aerosol properties, both seasonal and diurnal, is present and provides information of driving factors of aerosol variability at both the sites; 3) The contribution of regional sources seem to dominate over the local /sub-urban sources, in the IGP region bounda-ry layer; 4) Aerosol properties and specific humidity “passive tracer” based analysis clearly reveal that the mountainous terrain sites are under the influence of air from the plains due to convective transport processes enhanced by local and mesoscale topography. The results presented in this thesis are particularly useful, first, when examining the linkages of aerosol properties variability between two different environments. The second, in determining for instance local versus regional influences, and pollutants reaching high altitude sites which can be explained by boundary layer dynamics processes, especially in the mountain terrain where the modelled mixing layer depths have uncertainties. This work outlines future direction of multi-points measurements on vertical profile of atmospheric particles and local boundary layer over mountainous terrain where the atmospheric structure becomes much more complicated. Additionally, investigations including isotope-based analysis and modelling work over the Himalayan region are desirable to be able to describe better the transport of atmospheric aerosols from IGP to high altitudes and further up to Himalayan ice-pack and glaciers where aerosol deposition could have serious environmental impacts.
  • Moreau, Juulia-Gabrielle (Helsingin yliopisto, 2019)
    Ordinary chondrites are primitive materials of the solar system; they were subject to thermal and shock metamorphism during asteroid accretion and collision history. Shock-darkening is a shock metamorphic process which occurs in ordinary chondrites where iron sulphides and metals form a network of tiny melt veins, optically darkening the lithology. Together space weathering and shock-darkening can be a major factor in alteration of reflectance spectra, suppressing the 1 and 2 micron silicate absorption bands. S-complex asteroids, hosting ordinary chondrites, display silicate absorption bands. C/X-complex asteroids are either devoid of 1 and 2 micron silicate absorption bands or presenting a weak silicate absorption band at 1 micron. If shock-darkening can alter the spectra of S-complex asteroids, they can appear like C/X-complex asteroids and induce a mismatch in the asteroid distribution. This thesis provides an in-depth study of shock-darkening in order to determine the pressure-temperature conditions for shock melting of both iron sulphides and metals, in ordinary chondrites. In order to perform this study the following actions were required: I. observing shock wave interactions in heterogeneous mediums composed of silicates, metals, and iron sulphides, the principal components of ordinary chondrites II. quantifying post-shock heating and melting of the individual phases III. comparing my results with observations of shock metamorphism in ordinary chondrites IV. investigating on the best conditions to reproduce shock-darkening in shock-recovery experiments. In contrast to shock-recovery experiments, I adopted a numerical modelling method which calculated the post-shock heating and melting of individual phases and provided observation of shock wave interactions in heterogeneous mediums. The shock physics code iSALE was used on a mesoscale to study shock compression of ordinary chondrites. Using complex models, the numerical study lead to the following results: A) 40−60 GPa is the likely range for shock-darkening, dominated by melting of iron sulphides. B) Heterogeneous distribution of peak shock pressures and post-shock heating is caused by strong impedance contrasts between phases (with strong pressure increases through reflections from high density phases to lower density phases, e.g. metals to silicates). C) Special conditions, such as eutectic melting, hotspots from convergence of shock waves, or pore crushing, are necessary to melt metals. D) Porosity and pre-heating are important boundary conditions affecting shock metamorphism. E) Results from the mesoscale models are compatible to observations of shock metamorphism in ordinary chondrites. Finally, simulations of shock-recovery experiments showed that the reverberation technique may prevent shock-darkening from occurring. Compared to a single pressure load, the reverberation technique reduces the rise in entropy from super-imposing pressures, thus, if sufficient pressure for shock-darkening (40–60 GPa) is achieved, melting of iron sulphides or metals may not occur. Alternatively, I showed that spherical shock-recovery experiments, which use spherically induced shock waves to shock spherical samples, are ideal to study shock-darkening because the rise in entropy is directly related to the peak-shock pressure in the sample. With my results, a more in depth quantitative study of the volume of shock-induced darkened materials during asteroid collisions is now possible.
  • Norppa, Miika (Helsingin yliopisto, 2019)
    This doctoral thesis examines the development of the inner city of Helsinki during a long timespan, from the birth of the city to the present day (1550‒2018). The study inspects 1. How the inner city of Helsinki has been developed in different times, especially from the viewpoint of the city spaces and physical structures, but also from the viewpoint of functions and for what reasons, 2. How various international, especially European trends, of city planning and architecture have influenced the planning of Helsinki inner city in different time periods? 3. What kind of influence the local context, more closely the history of inner city neighbourhoods, has had on the development the neighbourhoods? 4. How the recent neighbourhoods have been formed and what kind of needs for further development there are in the inner city of Helsinki? The research material can be divided into seven categories: research literature, professional magazine material, archive material, interviews, newspaper articles, statistics and observation material. The central theoretical framework of the research consists of the theory of city roles. By city roles I mean those livelihoods that are crucial for the existence of the city and through which the the role of the city in the hierarchies and networks of cities is determined. City roles and changes in them have historically had a tremendous significance in the development of the inner cities. In the history of Hel-sinki, this study recognises several city roles that have considerably determined what has been built in the inner city of Helsinki during different times. Architecture has generally reflected the heyday of a city role. Some of the city roles of Helsinki have ceded, and new city roles have replaced them, but many roles have had continuity, and several city roles have accumulated during the centuries. The second theoretical perspective of the study is offered by the concept of path dependency. According to the path dependency theory, historical events and choices have influence on how the city appears physically and functionally and on what possibilities and challenges the city will have ahead in the future. The present study examines path dependency especially in the city planning and architecture of the inner city of Helsinki. It describes closely the international influences in the planning of the inner city of Helsinki in different times. The decisions that other cities have made and the paths they have chosen have influenced the planning of Helsinki. International influences on the planning of the inner city of Helsinki have mostly come from the Baltic Sea region and European cities, but especially during the second half of the 20th century also from the United States. The local context has also, in one way or another, always influenced and has been taken into account in the planning of the inner city of Helsinki. During the last few decades, after the long period of emphasizing suburban planning, focus in the city planning of Helsinki has moved towards more compact urban development. In the planning of the inner city, there has been a slow comeback of traditional, urban city construction. This change has been associated with changes in the city roles, especially the weakening of the industrial role and the strengthening of city roles related to services. The revival of the traditional elements of inner city building has not, however, been complete. There are still pivotal differences between modern and traditional urban building in architecture, building practices and in the way local services are organized. Although there has been many well-meaning and successful efforts to regenerate the inner city, there are still things to do. During the 21st century, Helsinki has succeeded extremely well in different international comparisons of cities. The current study speculates whether Helsinki has during the beginning of the 21st century had a golden era during which the city would have acted as an international forerunner and what obstacles there are to achieving or retaining such a position. Keywords: Helsinki, inner city, city roles, path dependency, urban planning, architecture, history of urban planning, history of architecture, urban history, urban geography, history of Helsinki, planning influences, city centres, development of city centres
  • Teittinen, Anette (Helsingin yliopisto, 2019)
    The patterns and drivers of microbial biodiversity remain less described and understood than those of larger organisms. Considerable knowledge gaps regarding microorganisms remain especially among small water bodies, which contribute significantly to biodiversity across northern landscapes. The main aims of this thesis were (1) to investigate microbial biodiversity patterns and multi-scale drivers along elevational gradients in subarctic streams and ponds; (2) to explore the effects of species niche characteristics and traits on elevational distributions of pond diatoms; (3) to test for the theory of island biogeography and to identify the factors affecting diatom biodiversity in boreal springs; and (4) to investigate the factors shaping diatom biodiversity along a land-use intensity gradient across boreal streams. To achieve these aims, small streams, ponds, and springs in the boreal and subarctic regions were sampled for microorganisms, and a variety of explanatory variables representing local environmental conditions, catchment properties and climatic and spatial factors were measured or derived from existing databases. The studied microbial groups comprised diatoms, cyanobacteria, and non-cyanobacteria (i.e., bacteria other than cyanobacteria). To examine the relationships between microbial biodiversity and explanatory variables, advanced statistical methods were used. The results showed that in the subarctic streams, diatom species richness or range size exhibited no consistent elevational patterns, whereas community similarity decreased primarily with elevational distance. Diatom communities among the streams were shaped by local-scale variables, such as water depth, and regional drivers, including dispersal and geographical factors. In the subarctic ponds, the richness–elevation relationship was unimodal for diatoms and cyanobacteria, whereas non-cyanobacteria richness declined with increasing elevation. Ponds at both ends of the elevational gradient harboured taxonomically unique microbial communities. The observed patterns were driven by hierarchically structured factors. The variation in species richness and uniqueness of diatom and cyanobacteria communities were best explained by local-scale variables, whereas non-cyanobacteria were also influenced by terrestrial productivity and elevation. Pond diatom distributions were also affected by species niche characteristics and traits: small size and strong acid tolerance were associated with a wider elevational distribution. At the community level, acidic ponds harboured functionally clustered communities. For spring diatoms, no species–area or species–isolation relationships were found; instead, local environmental variables and catchment characteristics were most strongly associated with species richness and community composition. At the relatively small spatial scale studied, diatom biodiversity was apparently not constrained by dispersal-related factors. Along the land-use intensity gradient, changes in stream diatom communities were evident. More intensive land use resulted in decreasing species richness and community compositions comprising more pollution-tolerant species. The variation in diatom richness and community composition was influenced by multiple local-scale factors, which in turn were controlled by catchment properties. In conclusion, this thesis expands current knowledge of microbial biodiversity across small water bodies in the northern regions. Microbial biodiversity in such systems is shaped by multiple factors prevailing at hierarchical spatial scales, the relative importance of which depends on the study system and microbial group. The effects of local-scale factors were emphasised throughout, yet catchment characteristics and spatial variables may also be important. For a deeper understanding of the factors underlying microbial biodiversity, considering multiple inherently different ecosystem types and organism groups is essential.
  • Kokkonen, Tom (Helsingin yliopisto, 2019)
    The processes related to urban development (urbanisation, densification, irrigation and worsened air quality) are assumed to affect the urban hydrological cycle, but little is known about the impact of the individual processes. One of the reasons for the knowledge gaps is the lack of measurements for the needed resolution or for the period of interest. Reanalysis products can provide the needed data, but those have not been evaluated in urban areas. Furthermore, model evaluation is commonly made against eddy covariance (EC) measurements, but little is known of the uncertainties related to often non-ideal instrument location at urban areas. To answer the uncertainties in urban hydrological cycle, Surface Urban Energy and Water Balance Scheme (SUEWS) forced with the WATCH Forcing Data is used. The analyses are performed in cities located in different climate conditions (Vancouver, London and Beijing) and above varying urban land covers (dense city centre and suburban areas). To understand better the uncertainties related to model evaluation, uncertainties of EC method are analysed using two identical EC systems at the same level close to each other in central Helsinki. The most crucial reanalysis variables to correct are precipitation due to coarse spatial resolution and the incoming solar radiation due to haze. SUEWS performs well when forced with corrected WATCH data, which allows detailed analysis of urban hydrological cycle. The irrigation has the dominant effect over densification and urbanisation on suburban hydrological cycle. The densification increases the runoff as much as the initial urbanisation, even though the increase of impervious surfaces is much smaller. The haze decreases evaporation which increases runoff and soil infiltration especially at smaller daily precipitation totals. This is expected to flush pollutants from surfaces and increase the pollutant loads of urban waters. After the post-processing of the EC data, systematic uncertainties in latent heat flux originating from a single-point observation above dense city centre due to removal of large fraction of wind disturbed data are only 8%. Thus, useful and representative EC observations can be obtained from urban areas, despite the errors induced by the non-ideal location. The results of this thesis answer the uncertainties in urban hydrological cycle by bringing new knowledge of the dominant factors in the urban water balance and the representativeness of reanalysis data in urban areas. The results can help urban planners to design sustainable cities being able to mitigate and adapt to the common problems in urban hydrology.
  • Hartmann, Marcelo (Helsingin yliopisto, 2019)
    Gaussian processes are certainly not a new tool in the field of science. However, alongside the quick increasing of computer power during the last decades, Gaussian processes have proved to be a successful and flexible statistical tool for data analysis. Its practical interpretation as a nonparametric procedure to represent prior beliefs about the underlying data generating mechanism has gained attention among a variety of research fields ranging from ecology, inverse problems and deep learning in artificial intelligence. The core of this thesis deals with multivariate Gaussian process model as an alternative method to classical methods of regression analysis in Statistics. I develop hierarchical models, where the vector of predictor functions (in the sense of generalized linear models) is assumed to follow a multivariate Gaussian process. Statistical inference over the vector of predictor functions is approached by means of the Bayesian paradigm with analytical approximations. I developed also new parametrisations for the statistical models in order to improve the performance of the computations related to the inferential task. The methods developed in this thesis are also tightly connected to practical applications. The main applications considered involve multiple species surveys and species distribution modelling in quantitative ecology. This is a field of research which provides a rich variety of applications where statistical methods can be put at test.
  • Ruotoistenmäki, Tapio (Geologian tutkimuskeskus, 2019)
    Adakitic plutonic rocks, or ‘adakitoids’, representing melts fractionated below plagioclase stability depths in the lower crust to upper mantle, cover a substantial fraction of the Finnish bedrock. Only some supracrustal sub-areas lack adakitic plutonic rock outcrops. In this study, I provide a summary of adakitoids in the Finnish Precambrian: their areal, chemical and physical variations and their evolution. The samples are considered on a regional to local area scale in fve separate sections. It is shown that adakitoids constitute a distinct chemically defned rock group, which overlaps groups defned by ‘traditional’ mineralogical and chemical methods. A very effective high-resolution tool for studying adakitoid chemistry is found to be the incompatible–compatible diagram (‘Pearce–Peate spectrum’) combined with normalization by geometric means of all Finnish plutonic rocks samples (AFP) from the Rock Geochemical Database of Finland (RGDB) maintained by the Geological Survey of Finland (GTK). The characteristics of adakitoids are considered by comparing their chemical spectra with those of granite and gabbro samples from the same database. The most distinct features of adakitoids are their relatively high Sr, Eu and ratios of LREE/HREE (light/heavy rare earth elements) and compatible elements/HREE. Moreover, their AFP-normalized spectra have relative maxima at Ba, K, Na2O, Ti, Li, CaO, V, Mn, Fe, Co and Mg. The adakitic plutonic rocks vary from granodiorites to tonalites and gabbros. The Proterozoic adakitoids are denser than Archaean adakitoids, reflecting their more mafc (sanukitoid) composition. However, their magnetic properties are alike. In Proterozoic sub-areas, the main characteristics of adakitoids and the average of all-plutonic rocks clearly differ, with the exception of two ‘oceanic’ sub-areas, whose spectral peaks coincide with those of the adakitoids, although with somewhat different trends. However, in Archaean sub-areas, the averages of all-plutonic rocks and adakitoids signifcantly correlate, which refers to similar evolutionary conditions and processes for both adakitoids and crust as a whole. In this study, the Proterozoic adakitoids are generally connected with ‘modern type’ plate tectonic processes, while Archaean crust and adakitoids (TTGs) are primarily connected with collision, stacking and over-/ underthrusting of inferred pre-existing microplates. However, in the Archaean Ilomantsi sub-area in eastern Finland, evolution related to ‘modern’, plate tectonic subduction is preferred. The chemical and mineralogical differences between adakitoids, sanukitoids and TTGs are obscure and overlapping. Therefore, straightforward association of these rock types with certain tectonothermal processes using tectonomagmatic geochemical discriminant diagrams must be carried out with care. The relative contents of pyroxenes, garnet and amphiboles in the restite of adakitic melts are evaluated by using the content ratios of trace elements, whose partition coeffcients for presumed basaltic source rocksdiffer substantially. The dominant restite minerals are interpreted to be clinopyroxene and orthopyroxene for both Proterozoic and Archaean adakitoids, while garnet and amphiboles also characterize the restites of Archaean adakitoids. The rapakivi granites correlate strongly negatively with adakitoids, thus giving indications of the characteristics of the complementary restitic material of the adakitoids. However, due to their complex uplift history, the rapakivis cannot be directly considered as adakitoid restites. Proterozoic adaki
  • Salo, Kari (Helsingin yliopisto, 2019)
    The purpose of this thesis is to support museums and other cultural institutes in their mission to attract young visitors by offering engaging experiences. The main goals of the the-sis were to develop a modular and easy-to-use audio story-sharing and audio-augmented reality platform, and evaluate the usefulness of the platform by measuring the level of engagement of participating youth in a workshop context. Design-science research methodology was used for audio platform component development, and mixed-methods were used to study the utility of platform components as case studies. At a more detailed level this means that the expandable and modular platform was developed incrementally one component at a time. When developing Audio Digital Asset Management, action research was used. For the Soundscape Mixer development, combined action research was used until the software was in the α phase after which a separate evaluation method was used in the β phase. For the Audiostory Sharing development de-sign-science research with separate building and evaluation methods was used. After implementation and testing the audio platform also from the usability angle, we moved on to engagement research. Workshops were organized in order to demonstrate the usage of the audio platform. During the workshops engagement was researched using mixed method, namely quantitative self-report questionnaires and qualitative methods in the form of observations. We have succeeded in developing a modular and versatile audio platform. All of the hardware is commonly used including Android phones. Software-wise the backend system is based on open source components. As the backend system provides relevant APIs, new mobile applications can be developed by third parties. In parallel, a concept was also developed, which helps to reach the young target audience and helps to measure the level of engagement. For this purpose, the student engagement structure has been applied in order to find out the level of engagement in workshops where the audio platform is a vital part. As a final summary, the results are promising. There is a general-purpose audio platform, which is modular, expandable and affordable for cultural institutions, and there is a concept to reach young people and a measurement instrument to measure the level of engagement in an audio-related workshop context.
  • Mannersalo, Paula (Helsingin yliopisto, 2019)
    ks. abstract.pdf
  • Korhonen, Johanna (Helsingin yliopisto, 2019)
    The hydrological regime is highly dependent on climatic conditions. In a boreal snow-driven region, such as Finland, changes in the winter and spring climatic seasonal conditions have a large effect on the hydrology. In this study, long-term changes and variability of the winter and spring season hydrological regime are investigated based on long-term ice phenology and river discharge time series in Finland. Ice cover and river discharge observations are among the oldest hydrological records in Finland and in some locations records cover 150–300 years. The analyses show statistically significant changes in both ice cover and discharge regime until the early 21st century. The ice freeze-up has become later, and the break-up is earlier, while the duration of the ice cover has shortened. In recent decades, changes have become even more apparent and the number of extremely early break-ups and late freeze-ups has increased. In ice phenology, new records have been set in the 21st century. Until 2002, there were both increasing and decreasing trends in the maximum lake ice thickness. Updated data until the winter 2017–2018 still show decreasing trends in the south, but no longer increasing trends in Central or Northern Finland. In the discharge regime, the seasonal winter and spring discharges have increased, and the spring peak has moved earlier up to 2004. The mean annual flows or annual high flows have not shown changes in general. Similar tendencies have even continued with updated data until the year 2017 as they did up to 2004. These observed seasonal winter and spring hydrological trends are in line with findings of annual and seasonal air temperature and precipitation changes and also with projected climate change scenarios until the late 21st century. In addition to long-term trend analysis, atmospheric circulation patterns and their relation to the seasonal winter and spring hydrological regimes were investigated. Both ice cover and river discharge are related to large scale atmospheric circulation patterns and show different periodicities. The influence of the North Atlantic Oscillation (NAO) can be seen in both the ice and discharge time series. The strong positive winter NAO is related to shorter ice cover duration and higher winter discharges, and the strong negative winter NAO vice versa. Keywords: climate change, Finland, hydrology, ice cover, river discharge, trends, variability
  • Kakko, Tia-Annette (Helsingin yliopisto, 2019)
    The separated wood components cellulose, hemicelluloses, and lignin allow for the production of various materials via chemical modifications. In addition to modifications, understanding the structural features of these products is important for enabling tailored processes for commodities. In this thesis, the introduction covers background information concerning cellulose chemistry. The dissolution of cellulose in various solvent systems is compared, and the usability of these solvents in acetylation of polysaccharides is assessed. Typically, the solvents used in Viscose or Lyocell processes are not suitable for chemical modifications, mainly due to their reactivity with either cellulose hydroxyls or used reagents. Furthermore, in current industrial cellulose acetate (CA) processes, the degree of polymerization (DP) of the product decreases. The results and discussion present the possibility of using ionic liquids as a reaction media for homogeneous acetylation of hemicelluloses and cellulose. The aim is to produce new methods in ionic liquids, in which tunable substitution is possible for acetylated hemicelluloses and CAs without substantial losses in DP. Furthermore, the procedure is upscaled and acetate fibers are produced with good spinnability and fiber characteristics in collaboration with Aalto University. Another issue under study is lignin chemistry, especially the structural characterization of hydrothermally (HT) treated Kraft lignin. The results demonstrate that diphenyl methanes are formed during HT treatment of Kraft lignin.
  • Benner, Christian (Helsingin yliopisto, 2019)
    The explosion of genomic data during the last ten years and the advent of Genome-Wide Association Studies (GWAS) have led to robust statistical associations between thousands of genomic regions and hundreds of phenotypes. However, any one associated genomic region can harbor thousands of correlated genetic variants, complicating the understanding of the underlying biological mechanisms that led to these associations. To address this problem, this doctoral thesis presents the development of the FINEMAP software for fine-mapping causal variants in these regions. In 2016, we solved the existing issue with the computationally expensive exhaustive search strategy of existing fine-mapping methods by implementing a Bayesian regression model and an ultrafast stochastic search algorithm in the FINEMAP software. We demonstrated that FINEMAP opens up completely new opportunities by fine-mapping the High Density Lipoprotein (HDL) cholesterol association to the LIPC locus with 20,000 variants in less than 90 seconds, while exhaustive search would require many years. With extensive simulations we further showed that FINEMAP is as accurate as exhaustive search when the latter can be completed and achieves even higher accuracy when the latter must be restricted due to computational reasons. Thus, FINEMAP is a promising tool for future fine-mapping analyses. Fine-mapping methods that use GWAS results also require Linkage Disequilibrium (LD) information as input in the form of estimates of pairwise correlations between variants. Motivated by feedback from FINEMAP users, we investigated in 2017 the consequences of misspecification of LD that could happen when publicly available reference genomes are used. We demonstrated both empirically and theoretically that the size of the reference panel needs to scale with the GWAS sample size to produce accurate results and we provided the LDstore software to help share LD estimates. This finding has important consequences for the application of all fine-mapping methods using GWAS results from GW AS consortia in which accurate LD estimates from each participating study are typically not available. In 2018, we implemented in FINEMAP an approach for estimating how much phenotypic variation can be explained by the causal variants. To demonstrate this, we applied FINEMAP to 110 regions across 51 biomarkers on 5,265 Finnish samples. We compared regional heritability estimation using FINEMAP with both the variance component model BOLT and fixed-effect model HESS in biomarker-associated regions, showing good concordance among all methods. Through simulations with biobank-scale projects, we also illustrated how violations of model assumptions on polygenicity or unspecified genetic architecture induces inaccuracy to the existing heritability estimates that becomes more accentuated as statistical power to identify causal variants increases. Ever increasing GWAS sample sizes, soon reaching millions of samples, provide unprecedented statistical power to decompose heritability estimates from polygenic models into heritability contributions from causal variants. In conclusion, this doctoral thesis shows that (1) the computational efficiency and accuracy of FINEMAP makes it a promising fine-mapping tool, (2) LD estimates need to be chosen more carefully than previously thought to avoid bias, and (3) large-scale data sets provide new opportunities for fine-mapping to deduce a variant-level picture of regional genetic architecture.
  • Äijälä, Mikko (Helsingin yliopisto, 2019)
    Climate change and degraded air quality rank among the most severe environmental problems that humanity currently faces. Atmospheric aerosols - the fine particles suspended in air – play a significant role in both of them. Aerosols affect Earth’s radiation balance via their interactions with radiation (scattering and absorption of light) and atmospheric water vapour (cloud formation, lifetime, brightness and rainfall). Overall, aerosols have a cooling effect on climate. When inhaled, aerosols can cause a range of adverse health effects, from allergies to lung disease and increased rates of cancer. Air pollution is estimated to result in millions of premature deaths each year in polluted environments. All of these aerosol effects and interactions significantly depend on their chemical compositions. This thesis focuses on aerosol chemical composition, measured by using mass spectrometry. To make sense of the vast diversity of chemical compounds present in the atmospheric aerosol particles, we rely on chemical classifications (speciations). In this work, different types of traditional aerosol mass spectrometric chemical speciations are evaluated by their ability to explain measured aerosol physicochemical properties, such as volatility, hygroscopicity and optical properties. While the parameter estimates for aerosol physicochemical properties derived from traditional chemical classifications do correlate with experimental data, the estimates fail to adequately capture the observed variabilities. Whether this is due to deficiencies in speciation schemes, flaws in assumptions or models or measurement uncertainties, is not apparent. However, it seems evident that there is room for improvement in all of the above-mentioned fields. During the course of this work, chemometric methods, (i.e. the application of mathematical and statistical methods to the analysis of chemical measurements) were implemented in the analysis of aerosol mass spectra. The results clearly show the value of statistics-based, machine learning oriented methods for feature extraction and chemical classification. Such chemometric approaches maximise the amount of information available for an analyst of aerosol mass spectrometric results, and enable making better informed interpretations. Combining methods such as data factorisation and clustering can overcome typical limitations of these methods when used as stand-alone techniques. Chemometrics-based, machine-learning-like methods thus show considerable potential for improving aerosol chemical analysis. Finally, chemometric tools were shown to be capable of producing new, comprehensive, mathematically and statistically robust chemical classifications, which again contribute to our understanding of the atmospheric aerosol properties, interactions and effects.
  • Järvelä, Jarkko (Helsingin yliopisto, 2019)
    Holography is an umbrella term covering conjectures relating strongly coupled quantum field theories and classical gravity theories. While originally intended to provide information about quantum gravity and string theories, the AdS/CFT correspondence has been applied to study many difficult problems in quantum field theories by considering suitable gravity duals. There are many long-standing problems in theoretical physics that have been hard to tackle. These include the confining nature of QCD and gluons, and the strange behaviour of some phases of high-temperature superconductors. These problems are not expected to have a valid quasiparticle description so a new paradigm might be needed to study these systems. A strong coupling approach via holography might be able to provide insight into these problems. Another new paradigm is provided by quantum information theory. Entanglement is important not only in quantum computing but also in describing fundamental properties of quantum field theories and states of systems. Our tools of choice are Rényi entropy, entanglement entropy and capacity of entanglement. This thesis provides a brief introduction to the methods of holography. We introduce important quantum information concepts and relate these to holographic quantities. We also provide evidence, why new physics is needed in condensed matter theory and provide two holographic approaches, the Einstein-Maxwell dilaton theory and the probe brane approximation. The latter saw extensive use in our research.
  • Pivovarova, Lidia (Helsingin yliopisto, 2018)
    This thesis addresses information extraction from financial news for decision support in the business domain. News is an important source of information for business decision makers, which reflects investors’ expectations and affects companies’ reputations. A vast amount of various news sources forces development of text mining algorithms to collect most crucial information and present to a user in a condensed form. The thesis presents the PULS media monitoring system and describes several news mining tasks, namely document clustering, multi-label news classification and text polarity detection. For each task, we present an end-to-end processing pipeline, starting from data preprocessing and clean-up. A particular attention is given to named entities (NEs), that are used as one of the inputs for all presented algorithms. Chapter 1 overviews the PULS news monitoring system and its niche within text mining for business intelligence. In Chapter 2 we propose a novel algorithm for news grouping, which uses NE salience and exploits a specific structure of news articles. In Chapter 3 we use automatically extracted NEs and entity descriptors in combination with keywords to improve SVM classifiers for large-scale multi-label text classification. Then, we propose a convolutional neural network (CNN) architecture that outperforms an ensemble of SVM classifiers for two different datasets. We compared various ways to represent NEs for CNN classifiers. In Chapter 4 we use a CNN classifier for entity-level business polarity detection. We compare three methods of re-using data annotated for a different though remotely related task and demonstrate that unsupervised knowledge transfer works better than other techniques that involve manual mapping.
  • Venäläinen, Annika (Helsingin yliopisto, 2018)
    The purpose of this thesis is to provide a better understanding of the properties of surfaces covered by self-assembled monolayers (SAMs) as well as the magnetic properties of interacting nanoclusters of gold and palladium. Surfaces covered by SAMs were studied by investigating their possible metallization as well as the morphological changes in bare and SAM covered Au(111) surfaces induced by Ar irradiation. The ferromagnetism in bare Au and Pd nanoagglomerates produced by nanocluster deposition was also investigated. SAMs used for this thesis are dodecanethiols (DDT, CH3(CH2)11SH) for the study on Ar ion induced morphological effects, as well as 4-mercaptopyridine (4-MPy) and two different kinds of dithiocarbamates (DTCs, R2NCS2) for the metallization study. The Au and Pd clusters were generated using a gas aggregation source in the low energy-range. Surface morphologies were studied by the use of scanning tunnelling microscopy (STM), transmission electron microscopy (TEM) and atom force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) was used to determine the chemical compositions of surfaces, whereas a superconducting interference device (SQUID) was utilized for magnetization measurements. Our results show that DDT covered surfaces are more susceptible for irradiation-induced surface morphology changes than the unmodified Au surfaces. Flame-annealing of a Au(111) surface prior to ion bombardment is also found to be more susceptible to irradiation-induced surface defects. Based on our results it also seems that SAMs of DDT, 4-MPy, DTC, and DTC2 are impenetrable for Pd clusters deposited at thermal energies. For assemblies of bare Au nanoclusters we present ferro- and superparamagnetic behaviour dependent on the interactions between particles. The enhanced surface-to-volume atomic ratio is found to favour ferromagnetism in the case of bare Au nanoparticles. For palladium nanocluster thin films we show that the ferromagnetic behaviour is highly dependent on the growth mode and film thickness, as these cause variations in the Pd cluster structures and resulting film morphologies.

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