Matemaattis-luonnontieteellinen tiedekunta

 

Recent Submissions

  • Lan, Hangzhen (Helsingin yliopisto, 2019)
    Traditionally, sampling and sample preparation can occupy up to 70-80% of total analysis time in an analytical process that calls for state of the art technologies to reduce the time and the labor needed. In addition, authorities and researchers increasingly demand more sensitive and reliable analytical methods. Solid phase microextraction (SPME) Arrow and in-tube extraction (ITEX) techniques meet these requirements by combining sampling and sample preparation procedures into one, resulting in decreased total analysis time and improved accuracy without any need for organic solvent. The type and amount of sorbent phase, which is immobilized on/in SPME Arrow and ITEX devices, volume of the system and affinity towards targeted analytes are the four main parameters that affect the sensitivity and capability of an analytical method. The main goals of this thesis were to develop new materials, useful as the extraction sorbent in SPME Arrow and ITEX devices, and to clarify their applicability for semi-automated and automated sampling and/or extraction systems for the analysis of volatile organic compounds (VOCs) in environmental, food and biogenic samples. Atomic layer deposition and molecular deposition-conversion methods were employed to fabricate directly iron, aluminum, and zirconium-based metal organic frameworks (MOFs) SPME Arrow coatings. The efficiency of these hydrophobic MOF coatings to isolate hazardous organic compounds from wastewater was evaluated. SPME Arrows were coated also with acidified zeolitic imidazolate framework-8 (A-ZIF-8), ordered mesoporous silicas (OMSs) and functionalized OMSs with different mesopore sizes and multidimensional pore-channel structures by dipping method. Extraction selectivities of these materials were systematically studied. The dipped coatings were reproducible and reusable. The applicability of electrospun and electroblown nanofibers as the packing materials of ITEX was also evaluated. Polyacrylonitrile (PAN) nanofibers with good gas permeability, thermal stability, and excellent affinity to VOCs made them a good alternative of commercial adsorbents for ITEX packing materials. Fully automated dynamic PAN-ITEX system on-line coupled to gas chromatography-mass spectrometry (GC-MS) for continuous analysis of VOCs in air was developed for long-term campaigns. The applicability of aerial drone as the carrier for SPME Arrow and ITEX devices was tested as well for passive and active air sampling in the field. The effects of accessories used in the sampling device, drone flight displacement and sampling location on the sampling results were evaluated. The results demonstrated the great potential of new materials as the extraction sorbents for SPME Arrow and ITEX. They provided better or similar performance in terms of extraction capacity, extraction selectivity and extraction kinetics when compared to commercial materials for enrichment and isolation of analytes from various sample matrices. Further, the developed SPME Arrow and on-line dynamic ITEX methods offered flexibility and versatility for analysis of VOCs. The drone was an ideal platform for miniaturized passive and active air sampling in remote and difficult access regions.
  • Hannula, Jani (Helsingin yliopisto, 2019)
    Research-based development of mathematics teacher education aiming at enhancing teacher knowledge has increased internationally during the 21st century. Such development is needed, as the research literature shows that teacher knowledge is associated with teaching practices and student achievement. Since the 1980s, the literature on teacher knowledge has been based on the distinction between subject matter knowledge and pedagogical content knowledge. This distinction separates pure mathematical knowledge from knowledge of learning and teaching mathematics. During the latest decades, social constructivism has been the major framework for developing teaching practices. One teaching strategy using social constructivism as a referent is problem-based learning that emphasises solving authentic problems, co-operation and open inquiry. In this doctoral dissertation, I report a design-based research that focused on strengthening the interplay between subject matter knowledge and pedagogical content knowledge in the context of Finnish mathematics teacher education. The aim of the study was to add knowledge of possibilities and challenges in enhancing teacher knowledge in the context of problem-based learning as well as to design a novel teacher-education course. The theory of social constructivism and the model of problem-based learning were utilised to guide the instructional design of the course. Conceptualisations of teacher knowledge and beliefs as well as mathematical thinking were used as domain-specific theories. To support the design process, two theoretical and one empirical problem analyses were conducted. Additionally, three case studies related to different phases of the design process were conducted. Each case study examined one of the three implementations of the course developed in the study. As is typical for design-based research, the results of the study can be divided into three viewpoints: 1) domain-specific theories, 2) design process, and 3) design artefact. The participants of the study (N=83) were pre-service teachers mainly studying for the master’s degree in mathematics education. The data included interviews, questionnaires as well as participants’ course tasks. Different forms of qualitative content analysis were used as the main method of data analysis. From the standpoint of domain-specific theories, the study supports prior research literature showing that pre-service teachers perceive a difference between the contents and methodology of university-level mathematics and that of school mathematics. This gap is evident both in secondary–tertiary transition and later in developing teacher knowledge. The results of this study emphasise that one central aspect in developing mathematics teacher education is taking into account the connections between informal mathematical thinking, emphasised at school, and formal mathematical thinking, emphasised at university. With respect to the research process, the major findings of this study concern the differences of teacher knowledge produced by the participants in different case studies. During the first implementations of the course, pre-service teachers concentrated largely on the development of pedagogical content knowledge in their course tasks. This emphasis supports prior research showing that pre-service teachers stress the role of pedagogical knowledge in the teaching profession. However, during the last implementation of the course, the teacher knowledge produced by the pre-service teachers was more aligned with the intended learning outcomes of the course. Additionally, the process gave insight into pre-service teachers’ perceptions of the problem-based-learning approach. In line with the prior research literature, these perceptions highlighted the possibilities of the approach in enhancing self-directed learning and co-operation. However, the participants also reported challenges related to workload and need for instruction. With relation to design artefact, the study stresses six central characteristics that need to be taken into account in developing teacher knowledge in line with social constructivism. These characteristics are: 1) supporting discussion and co-operative knowledge building; 2) supporting a student-centred approach; 3) solving authentic and interesting problems; 4) reflective learning and formative assessment; 5) research-based teaching; and 6) connecting the knowledge of mathematics as a discipline with the knowledge of mathematics as a school subject. The results of the study imply that a problem-based learning approach support several pedagogical consequences of social constructivism such as self-directed learning and use of diverse representations. Additionally, a problem-based learning approach can support the development of specialised content knowledge. Such knowledge includes knowledge of different representations of mathematical objects and applications of mathematics in science and technology. On the other hand, the development of horizon content knowledge seems challenging in problem-based learning. Such knowledge includes, for instance, the knowledge of the relationship between different mathematical concepts. This study provides possibilities for further research and development both within and outside of the chosen research paradigm. Within the paradigm, further research of the meaning of, the development of and pre-service teachers’ conceptions of horizon content knowledge is needed. On the other hand, the research can be extended, for instance, by focusing on affective factors of mathematical thinking in contexts similar to this study. The design artefact is transferable to other contexts such as class teacher education. Key words: teacher knowledge, mathematical thinking, social constructivism, problem-based learning, design-based research, mathematics teacher education
  • Rantala, Antti (Helsingin yliopisto, 2019)
    The presence of supermassive black holes (SMBHs) is ubiquitous in all massive galaxies in the local Universe. In the standard cosmological model, galaxies grow in a process of hierarchical merging and through accretion of matter from the intergalactic medium. Correspondingly, SMBHs grow by accreting gas from their surroundings and through merging with other SMBHs. Thus, present-day SMBHs are expected to have a complicated past merger history. Merging SMBHs leave imprints both on the central regions of their host galaxies and the gravitational wave background. In this thesis, which consists of four peer-reviewed publications, we investigate SMBH binary dynamics in realistic galactic environments and study the effect of merging SMBHs on their early-type host galaxies. For this research, a novel numerical simulation code KETJU was developed. The first two publications present the simulation code KETJU. The KETJU code combines the widely-used galactic-scale simulation code GADGET-3 and an extremely accurate small-scale SMBH dynamics integrator AR-CHAIN. The numerical methods used in KETJU and their practical implementation are thoroughly presented. In addition, we validate the performance of KETJU in comparison simulations with direct N-body codes used in the literature. The energy conservation of the code and parallel scaling behaviour are also demonstrated. We study the effect of the chosen stellar mass resolution on the evolution of the SMBH binaries in a series of galaxy merger simulations. We find that the dependence of the SMBH binary hardening rate on the mass resolution of the simulation is weaker if more realistic multi-component galaxy initial conditions are used. Finally, we show that with a proper treatment of SMBH dynamics in galactic-scale simulations, SMBH mergers are delayed by a few 100 million years compared to the SMBH merger criteria commonly used in the literature. The last two articles study the formation of large stellar cores in massive elliptical galaxies. Using KETJU, we run a series of early-type galaxy merger simulations with SMBHs to investigate the core scouring process responsible for creating cores in massive galaxies. We systematically study the effect of the initial SMBH mass and the initial stellar density profile slope on the surface brightness, the velocity anisotropy profiles and the core scaling relations of the merger remnant. Throughout the two studies we find that more cuspy initial stellar density profiles provide a better match to the final observed properties of core elliptical galaxies. We show that elliptical galaxies built up in a series of minor mergers have larger cores than major merger remnants, as expected, but on the other hand have less anisotropic velocity distributions in their core regions. Finally, we present a simple merger model which for the first time simultaneously produces an early-type galaxy with a flat central core, a tangentially biased central stellar population and kinematically decoupled central regions. These properties of cored early-type galaxies have previously been difficult to explain in one single formation scenario.
  • Muuri, Eveliina (Helsingin yliopisto, 2019)
    Käytetyn ydinpolttoaineen loppusijoituksen turvallisuusanalyysin sorptio- ja diffuusioparametrit on pääasiassa määritetty laboratorio-olosuhteissa. Ilmiöiden fysikaalinen käyttäytyminen voi kuitenkin olla erilaista eri mittakaavoissa, esimerkiksi laboratorio-olosuhteissa verrattuna luonnonolosuhteisiin. Tämä tunnetaan skaalaefektinä. Skaalaefektit voivat olla merkittäviä ja niillä voi olla merkitystä suuren mittakaavan mallinnuksissa, jotka käyttävät laboratoriokokeissa määritettyjä tietoja. Tämän väitöskirjan tavoitteena oli tutkia, kuinka laboratoriossa määritetyt sorptio- ja diffuusiotulokset voidaan skaalata in situ -olosuhteisiin. Tämä tehtiin määrittämällä 133Ba:n sorptio- ja diffuusioparametrit laboratoriokokeissa ja vertaamalla tuloksia Sveitsin Grimselissä toteutetun pitkäaikaisen in situ -diffuusiokokeen tuloksiin. Bariumin sorptiokäyttäytymistä tutkittiin tässä väitöskirjassa laboratoriossa tehdyissä eräsorptiokokeissa ja ohuthiesorptiokokeissa. Bariumin diffuusiota tutkittiin myös laboratoriodiffuusiokokeissa kivikuutioilla. Laboratoriokokeet tehtiin Grimselin ja Olkiluodon pääkivityypeille sekä pohjavesisimulanteissa, jotka tehtiin muistuttamaan Grimselin ja Olkiluodon pohjavesiolosuhteita. Bariumin sorptiotuloksia mallinnettiin PhreeqC-ohjelmalla ja diffuusiotulokset mallinnettiin PhreeqC-ohjelmalla sekä COMSOL Multiphysics -ohjelmalla. Lisäksi työssä kehitettiin uutta kvantitatiivista mittausmenetelmää bariumin aktiivisuuden jakautumisen mittaamiseen kivikuutioissa sekä ohuthieissä uudella elektronisella autografiamenetelmällä, BeaQuantTM:lla. Lopuksi 133Ba:n diffuusioprofiilit Grimselin in situ -diffuusiokokeesta määritettiin gammamittauksella ja autoradiografialla, ja tulokset mallinnettiin COMSOL Multiphysics -ohjelmalla. Tässä työssä selvitettiin, että bariumin laboratorio-olosuhteissa määritetyt sorptioparametrit ovat noin kaksikymmentäkertaiset verrattuna tuloksiin in situ -olosuhteissa. Tämä on tärkeää tietoa käytetyn ydinpolttoaineen loppusijoittamisen turvallisuusanalyysille, kun muunnetaan laboratoriokokeissa määritettyjä arvoja vastaamaan in situ- olosuhteita. Lisäksi työssä kehitettiin uutta elektronista autoradiografiamenetelmää, jotta sillä voitiin mitata 133Ba:n aktiivisuuden jakautumista graniittisissa kivissä kvantitatiivisesti.
  • Tiitola, Paavo (Helsingin yliopisto, 2019)
    In this thesis, I examine the currently most researched methods of supersymmetry (SUSY) breaking, a mechanism necessary to make the minimally supersymmetric extension to the Standard Model (MSSM) and its extensions consistent with the non-observation of the so-called superpartners of the Standard Model particles. In the first part of the thesis, I review the basic principles and features of SUSY, the MSSM, and SUSY breaking. In the remaining part, I present the results of the three publications that the thesis is based on. In the first of our papers, we used SUSY breaking mechanism dependent relations between gaugino mass parameters to estimate lower mass limits for neutralinos and charginos – few of the most promising candidates for near future experimental detection in SUSY. We then compared these limits in different SUSY breaking scenarios. We evaluated an upper bound on the mass of the lightest neutralino that follows from the structure of the mass matrix. We also examined the cosmological implications of the SUSY breaking mechanism by calculating its effect on relic density. We studied the branching ratios of particle decay in each type of mechanism. In the second paper, we studied the effect of including a so-called dimension five operator in the MSSM on neutralino and chargino masses and composition, and examined the implications on determining the SUSY breaking mechanism. We also examined the usefulness of two sum rules in determining the SUSY breaking mechanism in this model. In the final paper, we examined quantities known as renormalization group invariants (RGIs) from the point of view of SUSY breaking. We discussed the potential role of these scale-invariant combinations of masses and couplings in determining the nature of SUSY breaking by solving the SUSY breaking parameters in terms of the RGIs for a general model of SUSY breaking, the so-called deflected mirage mediation, which includes contributions from three main SUSY breaking mechanisms.
  • Stjernberg, Mats (Helsingin yliopisto, 2019)
    This PhD study in urban geography focuses on a distinct neighborhood type in Finland, namely suburban housing estates (lähiö). Although suburban housing estates are currently topical in Finland, as they are often associated with various problems, there has been little research concerning their development in the country at large during the last few decades. The purpose of this study is to overcome this shortage by analyzing the socio-economic and demographic development of suburban housing estates within the whole of Finland and in different types of regions. The focus is on suburban housing estates dating from the 1960s and 1970s, which was the main period of housing estate construction in Finland. The study examines what was characteristic of such estates in 1990 and 2010, and what kind of changes can be seen in their socio-economic and demographic position during this time span. Furthermore, the research examines suburban housing estates in three different sub-regional types: growing, stable and shrinking sub-regions. For conducting the analysis, a GIS-based approach was developed for defining, identifying and locating housing estates dating from the 1960s and 1970s within the whole Finnish territory. The empirical analysis of the research is based on examining the development of suburban housing estates according to both individual variables as well as multivariate methods (principle components analysis and cluster analysis) with the intention of uncovering the relationships between different facets of change. The research findings show that Finnish suburban housing estates dating from the 1960s and 1970s were usually relatively average neighborhoods in 1990, but since then they have generally witnessed noticeable socio-economic decline along with profound demographic changes. Also the attractiveness of these types of neighborhoods has gradually decreased over time. The study suggests that the development of suburban housing estates is closely linked to broader societal changes and particularly to the development of their wider regions. Although decline is evident in most Finnish housing estates, it is notable that not all estates are socio-economically disadvantaged. This underlines that housing estates are far from homogenous and that their development paths have been highly diverse. Overall though, based on the changes identified in this study, the public concerns related to this distinct type of concrete suburbia are in many ways valid, and from the perspective of Finnish urban and housing policy, suburban housing estates appear to be one of the most central challenges during the years to come.
  • Karhu, Juho (Helsingin yliopisto, 2019)
    The mid-infrared wavelength range is important for vibrational spectroscopy and trace gas detection, because it contains strong fundamental vibrational transitions. The extension of spectroscopic techniques into the mid-infrared wavelengths is a major area of development. This thesis describes sensitive spectroscopic measurements, which take advantage of the strong mid-infrared transitions to produce novel spectral data. The measurement setups are enhanced using optical frequency combs. Frequency combs are stable laser sources, which emit laser light over a wide optical spectrum. Their development was awarded with one half of the Nobel Prize in Physics in the year 2005. Frequency combs have found many applications in laser spectroscopy, because they combine the coherence and high brightness of a laser source with a wide optical spectrum. The stability of the frequency combs is valuable in high-resolution spectroscopy and metrology. This thesis is focused on two novel measurements: direct frequency comb spectroscopy of radiocarbon methane and double resonance spectroscopy of acetylene. In the former measurement, an optical frequency comb emitting in the mid-infrared region was used as the light source in broadband spectroscopy of radiocarbon methane. The carbon atom in the radiocarbon methane molecule is replaced by the radioactive carbon-14 isotope. High sensitivity was reached by combining a high-power mid-infrared frequency comb with cantilever-enhanced photoacoustic spectroscopy. The photoacoustic detector can take full advantage of the high power spectral density of the frequency comb. This measurement produced the first reported infrared spectrum of radiocarbon methane. In the double resonance spectroscopy measurements, a mid-infrared and a near-infrared light source were simultaneously used to excite two transitions of acetylene, with a shared energy state. This allows detection of spectral lines, which are normally absent in an acetylene infrared spectrum. The method also provides sub-Doppler resolution for determining spectral line positions with high precision. Because of the sub-Doppler resolution, instabilities of the light sources can begin to limit the precision of the measurements. A drastic increase in sensitivity was reached by stabilizing the light sources using frequency combs as references.
  • Rannikko, Janina (Helsingin yliopisto, 2019)
    This thesis focuses on experimental dental wear research and the palaeoecology of suids (Mammalia: Suoidea, pigs) of the late Miocene to Pleistocene (ca. 8-0.7 Ma) Turkana Basin, situated in present-day northern Kenya and southern Ethiopia. Most of the present-day suids are omnivorous, medium-sized, and inhabit forest or dense vegetation environments. An exception is the warthog in Africa, which is adapted to an open environment and mainly consumes grasses. What seems to be an exception today, appeared more commonly in the past. During the Plio-Pleistocene at least three different dominant suid genera within two different subfamilies in Africa (Notochoerus, Metridiochoerus and Kolpochoerus) consequently adapted towards grass-eating. Suids in the Plio-Pleistocene Turkana Basin lived in the same environments as early hominins. An omnivorous lifestyle and bunodont cheek tooth morphology describes both groups, but during the Plio-Pleistocene the suids rapidly evolved towards species adapted to abrasive food items, while hominins retained their bunodont tooth morphology. To better understand relationships between diets and dental wear patterns, an experimental dental wear study with a mechanical chewing machine was conducted. The aim was to investigate dental wear and enamel microwear patterns generated by different diets. The results showed that microwear patterns could not be distinguished between graze and browse diets, but the wear rate was higher in the grass diet than in the browse diet. In addition to the study of the fundamental dental wear, this thesis focuses on the relative abundance and diet preferences of the Turkana Basin suids. In the second study the relative abundance of four suid genera in the Turkana Basin from the late Miocene (ca. 8 Ma) to the late Pleistocene (ca. 0.7 Ma) was investigated in relation to the changing environment. The mostly unimodal patterns of the relative abundances, and the fact that the peak times of the genera were not overlapping, suggest that each genera had its own time of success in the Turkana Basin area. Finally, the dental surface topography of extant suids and African fossil suids was analysed to link the dental topography to specific diet preferences. The dietary ecologies of the present-day suids were possible to connect to their dental surface topography. Diets of the Plio-Pleistocene Turkana Basin suids were examined in relation to the present-day suids and Miocene suids. In terms of their dental topography, two of the extinct Turkana Basin suids appeared the most similar to the warthog, and two had similarities with both the warthog and the omnivorous suids. The results of this thesis extend scientific knowledge about the palaeoecology of the Turkana Basin Plio-Pleistocene suids, using the most extensive fossil database of the Turkana Basin as well as novel dental analysis methods: dental topography analyses were used extensively for the first time for suids and the chewing machine experiments were unique at the time in dental wear research.
  • Leino, Katri (Helsingin yliopisto, 2019)
    Atmospheric aerosol particles in different sizes have different impacts on climate and humans. Particularly in high concentration they may cause various negative health effects for people due to e.g. toxicity. Larger particles impact on the climate by absorbing or scattering the solar radiation and participating in cloud formation in the atmosphere. Some of atmospheric gases nucleate forming molecular clusters and grow in size to secondary aerosols. The phenomenon is called new particle formation (NPF) and it is contributing up to 50 % of the total aerosol number budget globally. In this thesis has focused on exploring NPF at different layers of atmosphere using a small aircraft as a platform for flying instrumentation and comparing with the data measured at ground level, SMEAR II, Hyytiälä. Based on the airborne and ground-based observations also the spread of wildfire emissions from Eastern Europe to Finland was studied. In case of studying NPF measurement flights over the SMEAR II (up to 3500 meters) were conducted during several campaigns between 2009 and 2017. We found out that NPF frequently occurs within the whole boundary layer (BL) and that the vegetation could be a key contributor in producing aerosol precursor gases in boreal environment. However, some signs were also found that NPF could occur separately in the residual layer or lower free troposphere. Emission sources produce different gases and particles into the atmosphere near the ground. Emissions can be divided to natural and anthropogenic. Example of a natural source is uncontrolled biomass burning in the forests and peat bogs, which is frequently observed around the world during warm and dry seasons. Air pollution from biomass burning is thought to have a significant influence on the chemical composition of the atmosphere and Earth’s climate system. In this study we investigated long-range transported air pollution in Finland originating from wildland fires in Eastern Europe in 2006 and 2010. The fire emissions were detected as increased concentrations of different gases and total number of particles at three SMEAR stations in Finland. The smoke plumes where detected also at higher altitudes during flight measurement campaign in summer of 2010. This study improves the understanding of the first steps of atmospheric NPF inside the BL and elucidates the impacts of air pollution originating from forest fires on air quality and climate after long-transport.
  • 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

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