Matemaattis-luonnontieteellinen tiedekunta

 

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  • Leppänen, Juho (Helsingin yliopisto, 2018)
    The thesis statistical properties of non-stationary dynamical systems with intermittency concerns two types of non-stationary dynamical systems: sequential compositions of interval maps with a neutral fixed point (Pomeau-Manneville maps) and intermittent quasistatic systems. Both systems are non-uniformly expanding and time-dependent, and (typically) lack invariant measures. The evolution of states under a sequential system is described by a sequence of varying self-maps of a phase space. Such constructions are motivated by applications to non-equilibrium processes in nature, where the map describing how a state evolves should depend on time. Quasistatic systems on the other hand draw inspiration from thermodynamics and model situations where the observed system transforms (infinitesimally) slowly with time due to external influence. At any given time the system is at an equilibrium, but over a long time span the equilibrium slowly changes. The thesis consists of an introduction and three scientific articles. The first and third article are about quasistatic systems, while the second article deals with sequential systems. The main result of the second article is a functional correlation bound widely useful for showing limit theorems in the sequential settting. We prove the result by modifying a technique of Liverani, Saussol, and Vaienti, which is based on a probabilistic approximation of the deterministic system. We present two applications of the result for a single Pomeau-Manneville map, by showing that the bound implies the correlation-decay conditions of the normal approximation methods due to Pène-Rio and Stein. Both methods yield a multivariate central limit theorem with an estimate on the rate of convergence. The rate produced by the former method is optimal with respect to the Kantorovich (or Wasserstein) metric. The latter method is suitable also for normal approximation in non-stationary settings. In the first article we introduce the intermittent quasistatic system and obtain several tools for further analysis of its statistical properties, including L^1-perturbation estimates for the transfer operators. The main result is an almost sure ergodic theorem for the time-averages of the model. The proof, which is partly based on a general theory developed by Stenlund, makes extensive use of the polynomial memory loss bound shown recently by Aimino et al. The third article builds on the results of the first two articles. By solving a well-posed martingale problem, we show that limiting distributional behavior of intermittent quasistatic systems can be characterized by a stochastic diffusion process. The result extends that shown by Dobbs and Stenlund for a class of uniformly expanding quasistatic systems.
  • Tuomisto, Maiju (Helsingin yliopisto, 2018)
    The rationale for this thesis was grounded on the general importance of finding novel, research-based chemistry teaching approaches to engage students in learning, because lower secondary students are commonly not interested in chemistry and their attitudes toward this subject are often negative. Educational games have been noted to promote motivation, interest and enjoyment in learning, but the research in the field has focused more on digital games than card and board games. There is also a need to develop quality evaluation criteria for educational games. Evaluation frameworks have been developed for digital games, but not for card and board games, and particularly not to support the use of educational games in chemistry education. In-game learning is the main purpose of educational games. Therefore learning with an educational game should be connected to a definition that explains how learning principles are tied to playing that game. In previous research, this line of reasoning has not been presented in studies concerning educational chemistry games. The main research problem in this thesis was: how do we support the design and evaluation of educational chemistry card and board games and in-game learning using them? From the research problem, three aims for the study have been derived: 1) to develop a practical and high-quality tool for designing and evaluating educational card and board games for chemistry education; 2) to design research-based educational games for chemistry education in order to support both the learning of central chemistry concepts and the use of this knowledge and related skills in different daily life situations; 3) to achieve understanding of the relationship between educational games and students’ concept development and transfer of knowledge in context-based learning. In order to achieve the aims, design challenges 1, 2 and 3 were executed in this study. This thesis followed the research-based principles of design-based research (DBR) and was based on a qualitative approach; hence qualitative research methods were executed in the problem analyses and game testing sessions of three design challenges (1–3) and their cyclic structures. Small-scale questionnaires, diaries, literature review, observations and video recordings were used as data collection methods. Data was analysed using content analyses and conversation analysis. Chemistry teacher educators, chemistry teachers, chemistry and home economics pre-service teachers, and students at upper and lower secondary levels participated in the six case studies of this study. Design challenge 1 aimed to answer research question 2: which features of an educational game may support the development of lower secondary students’ skills to learn and use a piece of information included in the periodic table? Two educational card games, Periodical Domino and Collect a Triplet, were designed to promote the development of lower secondary students’ ability to learn and use information included in the periodic table. Argumentation and construction of students’ own models of the periodic table were the two specific features in these games. In the first design cycle, the games were developed based on theoretical frameworks about games and educational games, and the results of empirical problem analysis, in which Finnish lower secondary students’ (n = 38, 8th grade) understanding of the periodic table and related topics, and their skills in using it, were studied using two small-scale questionnaires. As a result, information about specific difficulties among students in understanding the concepts related to the periodic table was discovered. The first versions of the games were tested on chemistry teachers (n = 22), on whom a small-scale questionnaire was used. As a result, feedback and suggestions for improving the games were achieved. In the second design cycle, the games were developed further based on the results. According to CHEDU Game design Tool, the games were found to satisfyingly fulfill the quality criteria for educational chemistry card games, and consistency between the evaluators was substantial (Periodical Domino κ = 0.756; Collect a Triplet κ = 0.718). According to evaluators, in these games in-game chemistry learning is supported by making thinking visible, application of knowledge and with suitable challenges in the zone of students’ proximal development. But improvements should be made at least in the categories of pre- and postgame evaluation and connection to the macroscopic level and daily life. Even though Periodical Domino and Collect a Triplet card games were research-based and based on theoretical frameworks developed to support learning, they have not yet been tested with students. Therefore, in this research, it was not possible to present evidence about their actual ability to support lower secondary students’ learning and use of skills regarding the periodic table. Design challenge 2 aimed to answer research question 1: what kind of game design and evaluation tool for educational card and board games supports both teaching and learning in chemistry education? The educational card and board game design and evaluation tool for lower secondary education (CHEDU Game Design Tool) was designed to support game developers and teachers in designing and evaluating quality educational games particularly for chemistry education purposes. In the first cycle of the design process, a theoretical problem analysis with integrative literature review was implemented. As a result, the elements of high-quality digital and non-digital games and educational games were uncovered. The tool was developed based on these features and the current Finnish national core curriculum for basic chemistry education. In the second design cycle, the tool was tested on chemistry and home economics pre-service teachers (n = 25), while game design diaries were kept and the tool supported the design process. As a result, information about pre-service teachers’ ability to benefit from the game design tool in their game design processes were achieved. The tool was further developed based on the results. The first version of the educational game design and evaluation tool was used in evaluation of the games developed in design challenge 1, and the second version was used in designing an educational board game in design challenge 3. Design challenge 3 aimed to answer research question 3: how does an educational game in a food and cooking context help students with development and transfer of knowledge between theory, everyday life contexts and hands-on activity? The Proteins in Backyard board game was designed to support lower secondary students in learning about protein chemistry, and in enhancing transfer of knowledge in daily life contexts and in hands-on activity. The theoretical framework about context-based learning, criteria in the CHEDU Game Design Tool and the results of two empirical problem analyses were exploited in the first cycle of the design process. In the first empirical problem analysis, pre-service teachers’ (n = 25) game design processes were analysed and as a result, information about specific quality game elements in their games was collected. In the second empirical problem analysis, upper secondary students’ (n = 22) interest and attitudes toward chemistry, food and cooking, and molecular gastronomy were studied using a small-scale questionnaire. As a result, information about their cooking behaviors, discussions related to chemistry and cooking, as well as their favourite topics in the field of molecular gastronomy were collected. The top three among these students were: fudges, cream foam and meringues. The board game was first tested on chemistry educators (n = 3) and, based on observation, feedback and video recording, important information concerning the game’s playability and video recording settings was collected. In the second cycle, the game was further developed and tested on 9th grade students (n = 6) using video recording, observation and a small-scale questionnaire. As a result, information about in-game activities, such as engagement, in-game learning and transfer of knowledge was collected. Based on the results, development and transfer of knowledge, as well as engaging game elements were noted to be apparent during play, but bridging them to hands-on activity was not observed. Based on the results, the game mechanics and difficulty level of missions in the playing cards in particular were further developed in the third design cycle for the game. This board game was found to fulfill the quality criteria for educational chemistry board games laudably, although there was still room for improvement – for example, increasing difficulty during play was missing. In general, in this thesis different design solutions were developed to draw on the research on educational games and chemistry education. The Periodical Domino and Collect a Triplet card games, the Proteins in Backyard board game and the CHEDU Game Design Tool are four guiding development models which follow the research-based design processes described in this thesis. Hence, in this study, four prescriptions for successful design processes were developed. During the design processes, descriptive and guiding theories were also developed. The results of this research suggested new theories about quality educational card and board games by revealing elements that play important roles in increasing the quality of non-digital educational games, and particularly in chemistry education. Simultaneously, the need to develop tools to systematically assess quality of educational games was answered. A theory about using educational game design as a part of chemistry teacher education was developed, and it was observed not just to support previous studies, but also to give new information about the quality game elements in the games designed by pre-service teachers. Also, a new theory about developing educational games to support chemistry learning and about in-game chemistry learning was developed. Theoretical bases for developing research-based quality educational chemistry games were presented so that design decisions concerning both game mechanics, game dynamics and game material were justified in a transparent manner, showing how they are designed to support possible in-game learning. These processes and embedding a hands-on activity into the board game make this study unique compared to previous research in the field. According to this study, when using quality educational games, in-game engagement and learning is possible at least via in-game transfer of knowledge in daily life contexts. This kind of research concerning in-game learning and in-game engagement has not been reported in the previous studies of educational games in chemistry education. However, due to the qualitative nature of this design research, these results are not generalizable, only indicative. This study presents theory and tools to use quality educational card and board games as an effective teaching approach in chemistry education, as well as providing ideas about how to carry out studies in the field of in-game learning research. It also offers ready-made tools, such as game materials, for chemistry teachers and teacher educators to apply in their teaching. KEYWORDS: chemistry education, context-based learning, educational game design, transfer of knowledge
  • Lagerblom, Kalle (Helsingin yliopisto, 2018)
    The selective oxidation of alcohols to aldehydes, ketones and carboxylic acids is among the pivotal reactions in organic chemistry. Traditionally, the transformation is conducted using stoichiometric amounts of heavy metal oxidants, which are costly and their use produces large amounts of hazardous waste. In this respect, the development of catalytic methods, which use oxygen as the oxidant and produce water as sole by-product, is crucial from the sustainable point of view. Recently, aerobic oxidation catalysts based on the combined used nitroxyl radicals and different co-catalysts have gained considerable amount of research interest due to their excellent performance in selective oxidation of alcohols under very mild conditions. The literature section of this thesis covers the selective aerobic oxidation of alcohols to carbonyl and carboxylic compounds with homogeneous catalysts based on the use of nitroxyl radicals together with different oxygen-activating co-catalysts. The experimental section presents the central findings and discussions from the author’s peer reviewed publications. In the first part, a catalytic oxidation method based on the combined use of nitroxyl radicals with Fe-based co-catalyst system is described. The method enables the oxidation of primary alcohols selectively either to aldehydes or carboxylic acids under mild conditions. The second part focuses on a catalyst system that is based on combined use of nitroxyl radicals and a Mn-based co-catalyst system. This catalytic method provides a highly practical way to selectively oxidize primary and secondary alcohols to aldehydes and ketones using simple reaction setup and workup procedures. The third section presents a further improved version of the aforementioned nitroxyl radical/Mn catalyst, which allows the oxidation of alcohols to be performed with very high efficiency using a small amount of catalyst.
  • Jääsaari, Jesse (Helsingin yliopisto, 2018)
    Fourier coefficients of cusp forms are interesting objects due to their arithmetic significance but we know very little about them in general. For instance, it is an interesting question, for a fixed form, to ask how these coefficients are distributed or how large their order of magnitude can be. Such coefficients are hard to study individually and therefore it is useful to have some other ways to study them. A classical theme in analytic number theory is to understand highly oscillatory objects, such as Fourier coefficients of cusp forms, by studying their sums and their correlations against other oscillating objects over certain intervals. Knowledge of sizes of above mentioned correlation sums can improve understanding of the nature of Fourier coefficients we are interested in. For example, if such a sum is large, this means that the Fourier coefficients and the test sequence oscillate similarly. This naturally leads to the exponential sums considered in this work. We study weighted sums of Fourier coefficients of Maass cusp forms against various oscillatory exponential phases. More specifically, we consider linear exponential phases. The sums over both long and short intervals are studied. The classical theory of Maass cusp forms (in which the underlying group is GL(2,R)) can be generalised to higher rank groups. In this thesis we consider both exponential sums involving Fourier coefficients of classical Maass cusp forms as well as Fourier coefficients of GL(n) Maass cusp forms with n>2. The thesis contains four scientific articles on the subject. The first and fourth article deal with short sums involving Fourier coefficients GL(n) Maass cusp forms. In the second article the size of rationally additively twisted sums involving Fourier coefficients of GL(3) Maass cusp forms is studied on average. To achieve this, a truncated Voronoi summation formula for such sums is established. In the third article various bounds for both long and short sums involving Fourier coefficients of GL(2) Maass cusp forms is proved.
  • Pyykkö, Joel (Helsingin yliopisto, 2018)
    Modern society produces vast amounts of digital data related to multiple domains of our lives. We produce data in our free time when browsing the net or taking photos with various personal devices, such as phones or ipads. Businesses and governments also gather a lot of information related to our interests, habits or otherwise personal information (legal status, health data, etc.). The amount of data produced is growning too large for us to be handled manually, and so to assist the user, specialized information retrieval systems have been developed to allow efficient perusal of different types of data. Unfortunately, as using such systems often requires expert understanding of the domain in question, many users get lost in their attempt to navigate the search space. This problem will only be exacerbated in the future, as the amount of data keeps growing, giving us less time to learn about the domains involved. Exploratory search is a field of research that studies user behaviour in situations, where users have little familiarity with the search domain, or have not yet decided exactly what their search goal is. Situations such as these arise when the user wishes to explore what is available, or is otherwise synthesizing or investigating the data. To assist the user in exploratory search and in finding relevant information, various methodologies may be employed, such as user modeling techniques or novel interfaces and data visualization techniques. This thesis presents exploratory search techniques for online personalization and feature representations that allow efficient perusal of unknown datasets. These methods are showcased in two different search environments. First, we present a search engine for scientific document retrieval, which takes the user's knowledge level into account in order to provide the user with more or less diverse search results. The second search environment aims at supporting the user when browsing through a dataset of unannotated images. Overall, the research presented here describes a number of techniques based on reinforcement learning and neural networks that, compared to traditional search engines, can provide better support for users who are unsure of the final goal of their search or who cannot easily formulate their search needs.
  • Ulvila, Ville (Helsingin yliopisto, 2018)
    In the current study, I experimentally demonstrate a new technique for generating a mid-infrared optical frequency comb (OFC). The motivation for this work stems from importance of coherent light sources to molecular spectroscopy, particularly in the mid-infrared region, where the strong fundamental molecular vibration-rotation absorption bands lie. Coherent light sources are needed to provide the best available sensitivity and selectivity in the spectroscopy experiments. As a prelude for the OFC research, an optical parametric oscillator operating close to signal-idler degeneracy was also examined in this thesis. The OFC generator investigated here is based on cascaded quadratic optical nonlinearities (CQNs), an approach that was first discovered as a part of the current study. By applying the new method inside a continuous-wave pumped optical parametric oscillator (OPO), a high-power mid-infrared OFC was produced by simple near-infrared laser pumping. Here, I present a rigorous experimental study of the new mid-infrared OFC generator. In particular, I verify the CQN comb mode spacing uniformity and demonstrate tuning of the center wavelength, offset frequency, and the mode spacing of the mid-infrared comb. I also apply a parametric seeding technique to improve the spectral quality of the comb. Furthermore, I demonstrate that the CQN method is capable of generating multioctave-spanning composite frequency combs. These results demonstrate the potential of the new OFC generation method for demanding molecular spectroscopy experiments. Utilization of an OFC source in field applications of molecular spectroscopy requires a robust and compact experimental platform. At the end of this thesis, I present preliminary results of our work towards miniaturization of the CQN comb generator using an optical waveguide device.
  • Mäkelä, Maarit (Helsingin yliopisto, 2018)
    Atomic layer deposition (ALD) is a thin film deposition method. Typically, an ALD thin film is deposited on a substrate in a heated reaction chamber in vacuum by exposing the substrate to ALD precursors. Commonly a metal precursor and a co-reactant, either an oxidizing or a reducing agent, are used. The film growth in ALD is self-limiting. Thickness of the film can be precisely controlled. ALD thin films are also conformal meaning that the films mimic the structures of the substrates. Plasma-enhanced ALD (PEALD) is an energy enhanced version of thermal ALD. The use of highly reactive radicals instead of the thermal co-reactant is the main difference between the thermal and plasma-enhanced ALD processes. The main drawback of PEALD is issued to be poor conformality of the PEALD thin films caused by the recombination of the radicals on the walls of the nanostructures. Potential applications of silver and gold thin films deposited by ALD include photonics, catalysis and electronics among others. In these applications conformal thin films with precisely controlled thickness are wanted. The main aim of this study was to develop thermal or plasma-enhanced ALD processes for these metals. Literature survey showed that there exist only a few ALD processes of silver and one PEALD study of gold. The main reason for the small number of processes has been the lack of thermally stable metal precursors. In ALD it is essential to have a thermally stable precursor to ensure the self-limiting growth. During this study several silver and gold compounds were evaluated for ALD. One silver, gold(I) and gold(III) precursor were chosen for the ALD experiments. The silver precursor was applied with plasma-activated hydrogen in a PEALD process and with a reducing agent in a thermal process. It exhibited self-limiting growth in both processes. An ALD gold process was developed with the gold(III) precursor applied with an oxidizing agent. The gold(I) precursor applied with a reducing agent produced pure gold thin films, but no self-limiting ALD process was established. The other aim of the study was to apply the silver PEALD process to two potential applications as case studies. Surface enhanced Raman scattering (SERS) substrates were coated with silver. Raman intensity of the adsorbed molecules on the silver surface was studied. Significant enhancement in the Raman response of the molecules on the SERS substrates was shown when compared to a neat solution. In the second study, the Ag process was applied to coat titanium dioxide nanotubes and nanoneedles on titanium implants. The silver nanoparticles on implants created an antimicrobial response. In both studies the main advantage of applying ALD was that the amount of silver deposited was precisely controlled.
  • Räty, Olle (Helsingin yliopisto, 2018)
    Increasing temperature is expected to intensify the hydrological cycle. The accompanied changes in (e.g.) snow cover, water availability and river flows impose challenges for several socio-economical sectors, whose operations are affected by these changes. The main question in these sectors is: how to cost-effectively adapt and mitigate to changes in the hydrological cycle? To answer this question, hydrological modeling run with regional climate model (GCM-RCM) simulations as input is typically required. To reduce biases in the GCM-RCM simulations before using them as input in hydrological modeling, adjustments with statistical tools, such as model output statistics (MOS), is required. While MOS methods have been tested comprehensively in the present-day climate, not much has been known about how they perform in transient climatic conditions. This gap is bridged in this thesis by evaluating a set of MOS methods designed for daily mean temperature and precipitation in a changing climate in Europe, using climate model simulations as proxies, i.e., pseudo-realities for the future. The main message from these exercises is that the identification of a single universally well-performing method is practically impossible, as the best performing method varies in time, space and between different distributional aspects. This conclusion is further strengthened when the selected methods are evaluated from the hydrological modeling perspective. Overall, several methods should ideally be used in impact studies. In addition to the pseudo-reality tests, the relative importance of MOS-method differences was compared against GCM-RCM differences as uncertainty sources both in real-world climate projections in Europe and hydrological simulations in Scandinavia. As the second message of this thesis, although climate GCM-RCM differences explain a larger part of the spread in future projections, MOS-method differences are non-negligible, when the high and low extremes are considered. In line with this result, MOS-method uncertainty has the largest contribution to the spread in projected changes of low and high flows.
  • Borke, Tina (Helsingin yliopisto, 2018)
    Water-soluble polymers are promising drug carrier materials. Especially polysaccharide graft copolymers are desirable for this purpose as they combine the favorable features of biopolymers, such as biocompatibility and biodegradability, with the controlled structure and functionality of synthetic polymers. This thesis examines water-soluble hyaluronic acid (HA) graft copolymers with cleavable arms as potential vehicles for sustained intravitreal drug delivery. Retinal diseases are the leading cause of visual impairment in the aging Western societies, but drug delivery to the back of the eye is complicated by multiple barriers. Intravitreal injections so far yield the highest bioavailability of drugs, however they need to be repeated frequently due to the rapid clearance of the therapeutics. Sustained delivery of drugs over extended periods of time is a promising strategy to prolong the injection intervals. Macromolecular drug delivery vehicles can help to reduce the clearance rate due to their high molecular weight and low diffusivity. The studied graft copolymers are based on a high molecular weight HA backbone and poly(glyceryl glycerol) (PGG) side chains attached via hydrolysable linkers. HA is a natural constituent of the vitreous and used to prolong the vehicle’s retention time in the eye. PGG is a multihydroxyfunctional polyether featuring a poly(ethylene glycol) (PEG) backbone and pendant 1,2-diol moieties in every repeating unit. As such, PGG possesses similar biocompatibility and antifouling properties as PEG, while being amenable to the conjugation of multiple drugs, probes and targeting moieties. HA was functionalized with hydrolysable alkynyl linkers for use in click grafting. The effect of modifications (i.e. amidation, esterification and click reaction) on HA properties was studied and the reaction conditions were optimized to minimize degradation while achieving efficient derivatization. Azido-functional PGG was prepared by ring-opening polymerization of epoxide monomers. Functionalization of PGG hydroxyl groups was explored to establish strategies for conjugation of drugs, probes and targeting molecules. For example, PGG could be efficiently labeled with rhodamine B boronic acid, due to formation of reversible boronic esters with the pendant 1,2-diol moieties. HA-PGG graft copolymers were prepared by copper-mediated azide-alkyne cycloaddition (CuAAC). The synthesized materials were studied under simulated physiological conditions to determine their stability and the cleavage of hydrolysable bonds. The HA backbone was stable during one month of incubation in buffer or vitreous liquid. The polymer-from-polymer release of PGG grafts from the HA-PGG ester copolymer was investigated and the hydrolysis rates were quantified. Hydrolytic cleavage of PGG chains from HA was significantly slower than cleavage of the small molecular weight alkynyl linkers, and was attributed to steric crowding at the ester bond. Hence, graft copolymers with cleavable arms have the potential to achieve longer lasting release than polymeric prodrugs with drugs attached directly to the backbone. The biocompatibility of PGG and HA-PGG copolymers was tested in cell cultures. The materials exhibited similar levels of cell viability as polyvinyl alcohol, which is FDA-approved for ocular applications.
  • Berg, Jeremias (Helsingin yliopisto, 2018)
    NP-hard combinatorial optimization problems are commonly encountered in numerous different domains. As such efficient methods for solving instances of such problems can save time, money, and other resources in several different applications. This thesis investigates exact declarative approaches to combinatorial optimization within the maximum satisfiability (MaxSAT) paradigm, using propositional logic as the constraint language of choice. Specifically we contribute to both MaxSAT solving and encoding techniques. In the first part of the thesis we contribute to MaxSAT solving technology by developing solver independent MaxSAT preprocessing techniques that re-encode MaxSAT instances into other instances. In order for preprocessing to be effective, the total time spent re-encoding the original instance and solving the new instance should be lower than the time required to directly solve the original instance. We show how the recently proposed label-based framework for MaxSAT preprocessing can be efficiently integrated with state-of-art MaxSAT solvers in a way that improves the empirical performance of those solvers. We also investigate the theoretical effect that label-based preprocessing has on the number of iterations needed by MaxSAT solvers in order to solve instances. We show that preprocessing does not improve best-case performance (in the number of iterations) of MaxSAT solvers, but can improve the worst-case performance. Going beyond previously proposed preprocessing rules we also propose and evaluate a MaxSAT-specific preprocessing technique called subsumed label elimination (SLE). We show that SLE is theoretically different from previously proposed MaxSAT preprocessing rules and that using SLE in conjunction with other preprocessing rules improves empirical performance of several MaxSAT solvers. In the second part of the thesis we propose and evaluate new MaxSAT encodings to two important data analysis tasks: correlation clustering and bounded treewidth Bayesian network learning. For both problems we empirically evaluate the resulting MaxSAT-based solution approach with other exact algorithms for the problems. We show that, on many benchmarks, the MaxSAT-based approach is faster and more memory efficient than other exact approaches. For correlation clustering, we also show that the quality of solutions obtained using MaxSAT is often significantly higher than the quality of solutions obtained by approximative (inexact) algorithms. We end the thesis with a discussion highlighting possible further research directions.
  • Valkama, Pasi (Helsingin yliopisto, 2018)
    There is an urgent need to decrease agriculture-contributed nutrient loading to surface waters. Excess amounts of phosphorus and nitrogen may lead to severe environmental problems, such as eutrophication and toxic algal blooms. Potential mitigation measures have been introduced to reduce loading, but their impacts on erosion, phosphorus and nitrogen loading are difficult to detect, due to challenging monitoring of diffuse (nonpoint) loading. Here, high-frequency on-line water-quality and -quantity monitoring (HFM) was used to detect the impacts of various agricultural mitigation measures on erosion, phosphorus and nitrogen loading on the catchment scale. We found that with discrete water samples, phosphorus load was more likely underestimated compared to sensor-based reference load. Gypsum reduced erosion and phosphorus loading very effectively in clayey agricultural catchment. Dissolved reactive phosphorus concentrations also became lower after gypsum application. The wintertime vegetation cover decreased the total phosphorus loads under mild winter conditions, when phosphorus loading is usually major. No impact on the dissolved reactive phosphorus concentration was observed. Small constructed wetland retained most of the incoming phosphorus and nitrogen loads during the growing season, but in spring and autumn the effectiveness was weak. Thus, a problem concerning wetlands as a mitigation measure is that they do not function efficiently during the critical times of load generation. In conclusion, we provide a guideline on how to develop future water-quality monitoring and how to assess the effectiveness of the various mitigation measures on the catchment scale. HFM can be used not only for estimating the impacts of agricultural mitigation measures, but also for providing more information on the water-quality impacts of land-use changes or impacts of stormwater treatment practices, as well as for developing models to produce more reliable scenarios for nutrient loading in changing climates. Mitigation methods such as gypsum and winter time vegetation, which are implemented in large field areas, are strongly recommended for reducing erosion and phosphorus loading in boreal agricultural clayey catchments. These mitigation measures are effective, particularly in mild winter seasons, and thus will also be beneficial under future climate conditions.
  • Keskiväli, Juha (Helsingin yliopisto, 2018)
    Abundant and inexpensive lignocellulosic biomass combined with the wide variety of terpenes, isolable from plants, have emerged as the strongest candidates to replace raw oil as a feedstock in the production of chemicals. Through catalytic modification, biomass feedstocks can be converted to various value-added products that can be utilized in a broad selection of applications. The literature review presents catalytic dehydration, hydrogenation and hydrodeoxygenation (HDO) as defunctionalization methods to synthesize value-added chemicals from multifunctional biomass-based substrates. For example, the hydroxyl groups of monosaccharides, sugar alcohols, and terpenoids can be removed with Brønsted or Lewis acid-catalyzed dehydration, generating versatile platform chemicals for mainly biofuel and polymer applications. Hydrogenation as a valorization method is presented through noble metal-catalyzed hydrogenation of C=C and C=O bonds of diverse lignocellulose-based substrates, for example, the conversion of monosaccharides to sugar alcohols. HDO is an efficient defunctionalization method for simultaneous reduction of unsaturated bonds and lowering the oxygen content of the substrates. Depending on the employed catalyst system, the reaction produces selectively or fully defunctionalized biomass-based products. The main themes of the literature review relate to the subject of the author’s articles published in peer-reviewed journals. The results and discussion section will cover the most significant findings and discussions from the author’s publications. The first part of the section describes new one-step HDO system for the conversion of enlarged furfural derivatives to biofuel compatible alkanes employing Eu(OTf)3 and Pd/C as deoxygenation and hydrogenation catalysts, respectively. The second part will cover the development and study of the new and recyclable Ru/C-based catalysts for the synthesis of isosorbide from lignin-containing cellulose. In the final part of the section, the findings of a robust and highly efficient transition metal triflate catalyzed dehydration of alcohols and terpenoids to olefins are reported. All the publications have significance in the field of biomass valorization and catalytic synthesis of sustainable chemicals.
  • Purisha, Zenith (Helsingin yliopisto, 2018)
    This thesis presents novel algorithms in X-ray computed tomography imaging using limited or sparse data: I. A non-uniform rational basis splines (NURBS) curve is used to represent the boundary of a target. Markov chain Monte Carlo (MCMC) strategy is applied for estimating the unknown curve from the projection data and an attenuation value of the target. In this case, the target is assumed to be homogeneous (it contains only one material). Instead of a single output, the solution of MCMC as a Bayesian framework is a posterior distribution. In addition, the results of the method are conveniently in CAD-compatible format. II. Adaptive methods for choosing regularization parameter are proposed. The first approach is called the controlled wavelet domain sparsity (CWDS). This is based on enforcing sparsity in the two-dimensional wavelet transform domain, and the second so-called the controlled shearlet domain sparsity (CSDS) in the three-dimensional shearlet transform domain. The proposed methods offer a strategy to automatically choosing regularization parameter where the end-users could avoid manually tuning the parameters. A known {\it a priori} sparsity level calculated from some available objects/samples is required. Both algorithms above have been successfully implemented for real measured X-ray data and the results using under-sampled data outperform the baseline method. The proposed methods incur heavy computation costs, however implementing parallelization strategy could save the computation time.
  • Zhou, Putian (Helsingin yliopisto, 2018)
    A large amount of biogenic volatile organic compounds (BVOCs) are emitted from boreal forests. Once emitted, BVOCs can be oxidized in the air, participate in particle formation and growth and thus indirectly affect local, regional and global climate. BVOCs act as a bridge between the biosphere and the atmosphere including atmospheric chemistry in both gas and particle phases. In this thesis we studied the in-canopy sources and sinks of BVOCs, the roles of BVOCs in gas and particle phases, as well as the impact of aerosol dynamics on the vertical aerosol fluxes in the planetary boundary layer. Several findings in this thesis are shown below: (1) By using a newly implemented gas dry deposition model in a one-dimensional chemical transport model SOSAA (model to Simulate the concentrations of Organic vapours, Sulphuric Acid and Aerosols) we simulated the in-canopy source and sink terms of 12 featured BVOCs. According to the strength of individual terms, BVOCs were classified into five categories: Cemis in which most of the emitted gases are transported out of the canopy, Cemis-chem in which most of the emitted gases are quickly oxidized inside the canopy, Cemis-depo in which emissions are comparable to deposition, Cdepo in which the dominant deposition sink leads to downward fluxes and Cchem-depo in which the chemical production compensates a part of deposition. (2) High upward fluxes of formic acid over a boreal forest were observed. The required unknown precursors and emission sources were quantified to explain the missing sources inside the canopy. (3) The simulated O3 concentration change due to chemical reactions related to BVOCs was in average less than 10% of the deposition sink. (4) The highly oxidized multifunctional organic molecules (HOMs) play a dominant role in the growth of new particles over the sub-Arctic forest region at the Pallas Atmosphere-Ecosystem Supersite and account for ∼ 75% of total SOA mass during new particle formation events. (5) The modelled vertical aerosol fluxes above the canopy caused by aerosol dynamics were comparable or sometimes exceeded that caused by particle dry deposition. This introduced large biases between measured flux and the particle dry deposition flux. The findings (1), (2), (3), (5) were obtained over the boreal forest at SMEAR (Station for Measuring ecosystem-Atmosphere Relations) II. This thesis provides a new numerical tool to analyse detailed sources and sinks of BVOCs, which can be applied in other ecosystems and further implemented in large-scale models.
  • Tenkanen, Tuomas (Helsingin yliopisto, 2018)
    Non-perturbative analysis provides the most accurate information about the properties of the electroweak phase transition in the Standard Model of particle physics. In this thesis, we initiate similar non-perturbative studies for three theories of physics beyond the Standard Model. Properties of the phase transition are important for both obtaining reliable predictions for potential gravitational wave background produced by this phase transition, and for viability of electroweak baryogenesis, that attempts to solve the problem of observed matter/antimatter asymmetry of the universe. In particular, we study three models with an extended Higgs sector: the Two-Higgs-Doublet Model, the real singlet and the real triplet extensions of the Standard Model. In all these models we have derived three-dimensional effective theories by using a method of high temperature dimensional reduction. The main result of this thesis is a set of dimensional reduction matching relations between parameters of effective theories and physical quantities in the aforementioned extensions of the Standard Model. In certain regions of parameter space for each model, we are able to perform a non-perturbative analysis simply by recycling lattice results obtained in the past. For a full analysis, new simulations are required, which goes beyond the scope of this thesis. In this thesis, we provide a brief introduction to the electroweak phase transition and electroweak baryogenesis. We then discuss both perturbative and non-perturbative approaches to the problem in greater detail. Finally, we summarise and discuss the results obtained so far, and outline future directions for research.