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  • Tuovinen, Hanna (Helsingin yliopisto, 2015)
    Northern Fennoscandia has experienced an unparalleled mineral exploration boom since around 2005. At the same time, there has been increasing awareness of the potential environmental impact of non-nuclear industries that extract and/or process ores containing naturally occurring radionuclides. Industrial activities may result in significant environmental problems if the waste generated during ore processing is not adequately managed. In 2010, a new project was launched with an objective to study the mobility of uranium series radionuclides from diverse mill tailings in a northern boreal environment in Finland. Three sites were investigated: the Talvivaara Ni-Cu-Zn-Co mine in central Finland, a former phosphate mine at Sokli, Finnish Lapland, and a former pilot-scale uranium mine at Paukkajanvaara, eastern Finland. The mobility of radionuclides from the mill tailings at Sokli was examined in order to assess the potential environmental impact of past and future mining activities. Mineralogical studies did not indicate that uranium or thorium have been mobilized from altered pyrochlore-group minerals in the Sokli ore or tailings. In the tailings pond, no clear trends were observed in the activity concentrations of uranium, radium or thorium isotopes in the surface layers of the mill tailings. In subsurface samples, an increase in the concentration of these isotopes can be seen when approaching the pond at the distal end of the sludge field. However, this increase is most likely to a consequence of compositional changes in material discharges. The results of the sequential extraction tests suggested that neither uranium nor thorium is in an exchangeable form and could potentially be released to the environment. Uranium (4% of the total concentration) was partly soluble under weakly acidic conditions, whereas thorium was tightly bound in mineral phases. At the former Paukkajanvaara uranium mine in Eno, the aim of the study was to examine the potential for further mobilization of radionuclides after remediation of the site in early 1990s. There are two primary sources of contamination at the site, the waste rock pile and the tailings. The results indicate that Ra-226 has been leached from the waste rock pile and accumulated in surrounding soil. In run-off sediment samples collected from a dry stream bed near the waste rock pile, the activity concentrations of Ra-226 and U-238 are higher than in soil samples. From the tailings, radionuclides can leach directly to the lake and to another small stream, which flows to the east of the waste rock pile. The results from the soil samples collected between the tailings area and the stream indicate leaching of U-238 and Ra-226 with the surface flow. Sediment samples collected from the bottom of the lake display pronounced uranium series disequilibrium with fractionation of Pb-210 and Ra-226 relative to the parent U-238. The results therefore indicate that leaching and accumulation of at least Ra-226 from the waste rock pile and possibly tailings is still ongoing. At Talvivaara, the aim of the study was to generate new data leading to a better understanding of the fate of radiotoxic uranium daughter nuclides, primarily Ra-226, Pb-210 and Po-210, in the mining process. In heap leaching, uranium is dissolved from uraninite to the pregnant leach solution. Uranium is probably transported as uranyl ions and uranyl sulfate complexes in the acid pregnant leach solution (PLS), and finally ends up in precipitates of the gypsum pond tailings via iron removal and final neutralization processes during the removal of residual metals. In terms of radiation safety, the U-238 activity concentration in the gypsum pond is partly above the exemption value (1000 Bq/kg) for natural radionuclides of the U-238 series. Radium and thorium mostly stay in the heaps during heap leaching. In addition, Pb-210 and Po-210 stay mainly in the heaps but slight mobilization of these nuclides was indicated. Secondary sulfate minerals, such as gypsum and jarosite, are precipitated from the sulfate-rich and acid PLS at Talvivaara. These minerals can incorporate radium in their crystal lattices, limiting Ra-226 mobility. Therefore, it can be assumed that most of radium and possibly part of Pb-210 and Po-210 are co-precipitated with poorly soluble sulfates in the Talvivaara heaps.
  • Lavinto, Mikko (Helsingin yliopisto, 2015)
    The science of cosmology relies heavily on interpreting observations in the context of a theoretical model. If the model does not capture all of the relevant physical effects, the interpretation of observations is on shaky grounds. The concordance model in cosmology is based on the homogeneous and isotropic Friedmann-Robertson-Walker metric with small perturbations. One long standing question is whether the small-scale details of the matter distribution can modify the predictions of the concordance model, or whether the concordance model can describe the universe to a high precision. In this thesis, I discuss some potential ways in which inhomogeneities may change the interpretation of observations from the predictions of the concordance model. One possibility is that the small-scale structure affects the average expansion rate of the universe via a process called backreaction. In such a case the concordance model fails to describe the time-evolution of the universe accurately, leading to the mis-interpretation of observations. Another possibility is that the paths that light rays travel on are curved in such a way that they do not cross all regions with equal probability. If some regions are favoured and others disfavoured, the average description of the concordance model gives incorrect results. My collaborators and I investigated the effects of voids on the CMB using second order perturbation theory and the exact Lemaître-Tolman-Bondi solution. A void has been detected in the direction of the CMB Cold Spot, but we found that contrary to the claims made in the literature, it was not large and deep enough to explain the Cold Spot. The results from perturbation theory and exact calculation agreed to a high precision, which was not surprising, as the void is fairly shallow. We have studied a toy model of the universe, called the Swiss Cheese model, to see if the model can produce observational signals that deviate significantly from the predictions of the concordance model. We studied the backreaction in such models, and concluded that in physically motivated Swiss Cheese models, its impact on the expansion rate must be small. We also considered an unphysical model that was constructed to have the holes expand independently from the background. Even though the inhomogeneities change the expansion rate completely, the backreaction contribution to the total average expansion rate today was only at 1% level. We also studied weak lensing in a more realistic Swiss Cheese model to see how the structures change the brightness and shape of sources. We found that the simplest assumption, no change in the average flux, seemed to be violated with a probability of 98.6%. Our results agree on the magnitude of the effect, in that it should be very small, but the exact value is significantly different. There are many reasons why this may be the case, and one of the reasons is that the structures alter the area of the constant-redshift surface around the observer. However, to find conclusive proof of this, the calculation should be re-done with a higher resolution.
  • Stén, Johan Carl-Erik (Springer / Birkhäuser, 2015)
    The Finnish mathematician and astronomer Anders Johan Lexell (1740-1784) was a long time close collaborator and the academic successor of Leonhard Euler at the Imperial Academy of Sciences in Saint Petersburg. Lexell was invited in 1768 from his native town of Åbo (Turku) in Finland to Saint Petersburg to assist in the laborious mathematical processing of the astronomical data from the forthcoming transit of Venus of 1769. A few years later he became an ordinary member of the Academy. Lexell was the first mathematician and astronomer of international renown from Finland. This thesis is the first full-length intellectual biography devoted to Lexell and his prolific scientific output. Using his numerous publications, we trace the development of his scientific thought. In close collaboration with Euler, he contributed especially to infinitesimal calculus and geometry. In astronomy his work pertains mainly to the parallax and longitude problems, as well as to orbit calculations. He is known for having recognised that Herschel's new "comet" of 1781 moves in a nearly circular orbit and must therefore be a planet. Lexell also predicted the extraordinary motion of the comet of 1770 ("Lexell's comet"), which constitutes an example of a restricted three-body problem. Lexell had wide scientific interests. Being internationally minded and well-connected, he entertained a rich correspondence not only with astronomers and mathematicians but also with natural historians and administrators. His detailed letters especially from his grand tour to Germany, France and England in 1780-1781 reveals him as a lucid observer of the intellectual landscape of enlightened Europe.
  • Ding, Yi (Helsingin yliopisto, 2015)
    Due to the popularity of smartphones and mobile streaming services, the growth of traffic volume in mobile networks is phenomenal. This leads to huge investment pressure on mobile operators' wireless access and core infrastructure, while the profits do not necessarily grow at the same pace. As a result, it is urgent to find a cost-effective solution that can scale to the ever increasing traffic volume generated by mobile systems. Among many visions, mobile traffic offloading is regarded as a promising mechanism by using complementary wireless communication technologies, such as WiFi, to offload data traffic away from the overloaded mobile networks. The current trend to equip mobile devices with an additional WiFi interface also supports this vision. This dissertation presents a novel collaborative architecture for mobile traffic offloading that can efficiently utilize the context and resources from networks and end systems. The main contributions include a network-assisted offloading framework, a collaborative system design for energy-aware offloading, and a software-defined networking (SDN) based offloading platform. Our work is the first in this domain to integrate energy and context awareness into mobile traffic offloading from an architectural perspective. We have conducted extensive measurements on mobile systems to identify hidden issues of traffic offloading in the operational networks. We implement the offloading protocol in the Linux kernel and develop our energy-aware offloading framework in C++ and Java on commodity machines and smartphones. Our prototype systems for mobile traffic offloading have been tested in a live environment. The experimental results suggest that our collaborative architecture is feasible and provides reasonable improvement in terms of energy saving and offloading efficiency. We further adopt the programmable paradigm of SDN to enhance the extensibility and deployability of our proposals. We release the SDN-based platform under open-source licenses to encourage future collaboration with research community and standards developing organizations. As one of the pioneering work, our research stresses the importance of collaboration in mobile traffic offloading. The lessons learned from our protocol design, system development, and network experiments shed light on future research and development in this domain.
  • Laaksonen, Antti (Helsingin yliopisto, 2015)
    This thesis studies two problems in music information retrieval: search for a given melody in an audio database, and automatic melody transcription. In both of the problems, the representation of the melody is symbolic, i.e., the melody consists of onset times and pitches of musical notes. In the first part of the thesis we present new algorithms for symbolic melody search. First, we present algorithms that work with a matrix representation of the audio data, that corresponds to the discrete Fourier transform. We formulate the melody search problem as a generalization of the classical maximum subarray problem. After this, we discuss algorithms that operate on a geometric representation of the audio data. In this case, the Fourier transform is converted into a set of points in the two-dimensional plane. The main contributions of the first part of the thesis lie in algorithm design. We present new efficient algorithms, most of which are based on dynamic programming optimization, i.e., calculating dynamic programming values more efficiently using appropriate data structures and algorithm design techniques. Finally, we experiment with the algorithms using real-world audio databases and melody queries, which shows that the algorithms can be successfully used in practice. Compared to previous melody search systems, the novelty in our approach is that the search can be performed directly in the Fourier transform of the audio data. The second part of the thesis focuses on automatic melody transcription. As this problem is very difficult in its pure form, we ask whether using certain additional information would facilitate the transcription. We present two melody transcription systems that extract the main melodic line from an audio signal using additional information. The first transcription system utilizes as additional information an initial transcription created by the human user of the system. It turns out that users without a musical background are able to provide the system with useful information about the melody, so that the transcription quality increases considerably. The second system takes a chord transcription as additional information, and produces a melody transcription that matches both the audio signal and the harmony given in the chord transcription. Our system is a proof of concept that the connection between melody and harmony can be used in automatic melody transcription.
  • Halme, Mia (Helsingin yliopisto, 2015)
    Toxic and incapacitating chemicals are ubiquitous in everyday life. Despite the prohibition of chemical weapons by the Chemical Weapons Convention (CWC), many toxic chemicals are still used: as legal riot control agents, in various processes and products of the chemical industry or as pesticides in agriculture. Validated analytical methods and knowledge of metabolism are therefore needed for the verification of possible intentional or unintentional exposures in carrying out occupational tasks or in civil incidents. The most reliable retrospective detection and confirmation of exposure to chemicals are achieved by analyzing unequivocal metabolites such as biomarkers, from biological samples, which have mainly been obtained from exposed persons, animals and experimental animal models. However, the use of animal testing for evaluating the safety and effects of chemicals that are known to be toxic or incapacitating raises ethical questions. Therefore, the use of an in vitro metabolism study approach to predict in vivo metabolite profiles, prior to obtaining more detailed knowledge in vivo could be a preferable strategy for evaluating the toxicology of these chemicals. Four toxic and incapacitating chemicals listed in the CWC or used for riot control were studied in this thesis, namely: sulfur mustard, capsaicinoids, chloropicrin and saxitoxin. The suitability of the conventional in vitro metabolism studies were assessed in this research. These assessments were achieved by using various mass spectrometric (MS) methods to screen and identify the formed metabolites. The validations of analyses methods for known biomarkers were carried out according to the current bioanalytical validation guidelines and identification criteria. The conventional in vitro metabolism studies used for sulfur mustard, capsaicinoids and chloropicrin, yielded new knowledge about the metabolic reactions and produced several novel metabolites by oxidative reactions and GSH conjugation. However, their clinical usefulness to serve as biomarkers of exposure in humans requires further studies. Quantitative fit for purpose analysis methods were optimized and validated for the following chemicals: saxitoxin, two b-lyase metabolites of sulfur mustard, and nitromethane as a metabolite of chloropicrin. All methods were found to be accurate and linear and fulfilled the general identification criteria.
  • Laaksonen, Tiina (Helsingin yliopisto, 2015)
    The detection of enantiomeric purity is an important part of synthetic chemistry. Especially when developing medicinal compounds the determination of the amount of enantiomeric impurities is important as one of the enantiomers may be poisonous or lethal to humans. Various methods exist for the study of enantiomeric purity and NMR spectroscopy has been intensively studied as a tool for this purpose. As NMR is fast, readily available and easy to use it provides an attractive way to study enantomeric purity. In NMR chiral discrimination is obtained by using chiral derivatising agents (CDAs) or chiral solvating agents (CSAs). CSAs have more potential in enantiomeric excess (ee) studies than CDAs as they lack of the disadvantaged of CDAs (e.g. kinetic resolution and racemisation). As chiral carboxylic acids are important in the synthesis of medicinally attractive compounds, natural products and their metabolites, CSAs which can be used for the determination of enantiomeric purity of carboxylic acids and are easily available and cheap are helpful. The present study mainly focuses on the development of CSAs suitable for the discrimination of non-ionic and ionic chiral carboxylic acids. (+)-Dehydroabietylamine was used as chiral building block for these new CSAs as it has several beneficial features such as easy availability, low price, an amenable structure for CSA construction and it is known to resolve chiral carboxylic acids via cystallisation. Three different series of non-ionic and ionic CSAs were developed from (+)-dehydroabietylamine: 1) ammonium, 2) secondary amine and 3) imidazolium based CSAs. Their enantiomeric discrimination abilities were examined with Mosher s acid and its tetrabutylammonium salt. Best resolution was obtained with non-ionic substrate and non-ionic CSA and with ionic substrate and ionic CSA. Ionic CSAs were also able to resolve non-ionic substrates but the enantiomeric resolution remained poor. The best performing CSAs were subjected for more detailed investigation. The stoichiometry of formed diastereomeric complex between the CSA and substrate was studied by titration experiment. CSA-substrate complexes were generally formed in 1:1 ratio. CSA applicability to function in ee determination was studied and they were able to detect the enantiomeric purities of samples with excellent reliability. Finally their ability to resolve various α-substituted carboxylic acids was studied showing that (+)-dehydroabietylamine based CSAs are suitable for chiral carboxylic acids containing electronegative α-substituent. Also the effect of measurement conditions and sample preparation when using cationic CSAs in enantiomeric discrimination was investigated. Lower temperatures and low polarity solvents were noticed to increase enantiomeric discrimination, among high CSA concentration. Delocalisation of negative charge in counter anion of CSA as well as the use of organic counter cation for the substrate was also notised to increase enantiomeric discrimination.
  • Lindqvist, Markus (Helsingin yliopisto, 2015)
    Hydrogen activation and subsequent hydrogenation reactions are commonly catalyzed by transition metal complexes. Lately it has been shown that these reactions can be performed using metal free main-group compounds, so called frustrated Lewis pairs , as catalysts. The literature review of this thesis gives a detailed discussion about these Lewis acids and Lewis bases pairs that, due to constructional strain, cannot quench each other s reactivity through adduct formation. They form reactive pockets that only fit small molecules. These are exposed to simultaneous reactivity of the Lewis acid and the Lewis base when entering the void. This might result in polarization and consequential reaction between the small molecule and the frustrated Lewis pair e.g. the reaction between the diatomic hydrogen molecule and a frustrated Lewis pair results in H-H heterolytic bond cleavage forming a reactive salt that can be used for further reductive reactions. In this work, the first example of oxygen Lewis bases in frustrated Lewis pair induced hydrogen activation is presented. This concept has later been developed, by others, to enable catalytic hydrogenation of carbonyls into alcohols. This is considered a breakthrough in frustrated Lewis pair chemistry. Aiming for asymmetric hydrogenation catalysts, the author focused on chiral frustrated Lewis pairs. Attempts to utilize camphor-backbones, did not result in the expected frustrated species. Yet, this seemingly dead-end revealed an intermediate frustrated state, in an internal acid-base equilibrium, facilitating reactions with hydrogen. Continuing with the concept, the terpene backbone was exchanged for a binaphthyl one. The free frustrated pair was formed, facilitating rapid and reversible reaction with hydrogen. The binaphthyl-derivative could also be used as a catalyst in asymmetric hydrogenations and up to 99% enantiomeric excesses were obtained. This is by far the best result obtained in asymmetric hydrogenations catalyzed by frustrated Lewis pairs. The presented catalyst can easily be modified to suit ones needs or used as such in the synthesis of chiral product, e.g. drugs or natural products.
  • Zhao, Kai (Helsingin yliopisto, 2015)
    Understanding urban human mobility is crucial for various mobile and network applications. This thesis addresses two key challenges presented by mobile applications, namely urban mobility modeling and its applications in Delay Tolerant Networks (DTNs). First, we model urban human mobility with transportation mode information. Our research is based on two real-life GPS datasets containing approximately 20 and 10 million GPS samples. Previous research has suggested that the trajectories in human mobility have statistically similar features as Lévy Walks. We attempt to explain the Lévy Walks behavior by decomposing them into different classes according to the different transportation modes, such as Walk/Run, Bike, Train/ Subway or Car/Taxi/Bus. We show that human mobility can be modelled as a mixture of different transportation modes, and that these single movement patterns can be approximated by a lognormal distribution rather than a power-law distribution. Then, we demonstrate that the mixture of the decomposed lognormal flight distributions associated with each modality is a power-law distribution, providing an explanation for the emergence of Lévy Walks patterns that characterize human mobility patterns. Second, we find that urban human mobility exhibits strong spatial and temporal patterns. We leverage such human mobility patterns to derive an optimal routing algorithm that minimizes the hop count while maximizing the number of needed nodes in DTNs. We propose a solution framework, called Ameba, for timely data delivery in DTNs. Simulation results with experimental traces indicate that Ameba achieves a comparable delivery ratio to a Flooding-based algorithm, but with much lower overhead. Third, we infer the functions of the sub-areas in three cities by analyzing urban mobility patterns. The analysis is based on three large taxi GPS datasets in Rome, San Francisco and Beijing containing 21, 11 and 17 million GPS points, respectively. We categorize the city regions into four categories, workplaces, entertainment places, residential places and other places. We show that the identification of these functional sub-areas can be utilized to increase the efficiency of urban DTN applications. The three topics pertaining to urban mobility examined in the thesis support the design and implementation of network applications for urban environments.
  • Neitola, Kimmo (Helsingin yliopisto, 2015)
    Aerosols affect our everyday life in many ways. Changes in visibility, allergies to pollen, spray cans and dosing of some medication are just a few examples of common aerosols. Aerosols may have more profound way to affect every one of us; through climate. Possible changes in aerosol particle concentrations and compositions may alter large precipitation patterns and change cloud albedo, and lifetime. To be able to predict future changes in climate, profound understating of physical and chemical processes affecting the atmospheric aerosol population is crucial. Nucleation, i.e. gas-to-liquid phase transition, is the fundamental step in particle formation in the atmosphere. Sulphuric acid is established to be one of key components in atmospheric nucleation, but other stabilizing species are needed to participate in the process to ex-plain atmospheric nucleation. The identity of these species and the mechanisms of the process itself have been elusive. This thesis aims to gain insight on the species participating nucleation and the mechanism of the whole process. This thesis concentrates first to identify meteorological parameters controlling the atmos-pheric new particle formation. The information gathered from the field is used to design laboratory experiments more precise for the purpose of studying nucleation. The laboratory experiments were carried out using different flow tubes, first to test the limits of the Clas-sical Nucleation Theory and later on to investigate sulphuric acid-water binary and sul-phuric acid-water-base compound ternary nucleation. The precursor gas species were measured using mass spectrometers and ion chromatographs. The measured concentration of sulphuric acid from gas and particle phases were compared to theoretical prediction. The magnitude of the effect of base compounds on nucleation was estimated. The clustering of sulphuric acid molecules with other species was detected. Initial growth of clusters were studied in the point of view of sulphate containing species. The results from the laboratory experiments confirmed earlier results found in the literature that base compounds increase nucleation rates significantly. The measurements of the gas-phase concentrations of these compounds set an upper limit, where the increasing effect is saturated. Comparison of the sulphuric acid concentrations measured with different tech-niques and with the theoretical approach showed order-of-magnitude discrepancy. The discrepancy was found to be due to clustering of sulphuric acid molecules with various species. Sulphate-containing species was found to be responsible of the initial growth of clusters in the flow tube measurements. Even though the species participating nucleation are still an open question, the work done in this thesis has helped to identify few of these species and the magnitude of their effect on nucleation. This thesis also helps to under-stand the initial growth of clusters in flow tube experiments and to identify possible limitation on instruments used commonly in atmospheric measurements.
  • Hirvonen, Sami-Pekka (Helsingin yliopisto, 2015)
    Poly(benzimidazobenzophenanthroline) (BBL), which may be doped into a p- and n-type semiconductor, has been chemically modified to enhance its processability. In its pristine form BBL is processable only in some concentrated acids and nitromethane/Lewis acid solutions. The corrosiveness of these solvents and moisture sensitivity of the solutions severely limits the possibilities for the use of BBL as an electroactive material in organoelectronic devices and limit the possibilities for its post synthetic chemical modification. In this work processable BBL derivatives have been prepared using two different approaches i) preparation of block-copolymers by attachment of water soluble polymers on BBL functional chain ends ii) attaching bulky side groups on one of the monomers and using that as a starting material in the polymerization reaction. Short BBLs of DP 10 or 20 were prepared with functional chain ends and monofunctional poly(ethylene oxide) (PEO) or poly(N-isopropylacrylamide) of several different molecular weights were attached at the chain ends. Elemental analysis showed that the extent of chain end substitution varied quite a lot when PEO was used. It was also shown that thermogravimetric analysis (TGA) was not suitable to determine the fraction of PEO in BBL-PEO block-copolymers. However, the extent of chain end substitution using PNIPAM was evaluated using TGA. BBL-PEOs could be processed into aqueous dispersions at concentrations ≥ 1.5 mg/ml by means of ultrasonication, and these dispersions were proven to be colloidally very stable. The dispersions could be used to spin- or drop cast films. At higher concentrations BBL-PEO dispersions were shown to form gels. The reason for the gelling is the packing of the polymer into nano-wire structures which then aggregate into 3D-network. SEM- and cryo-TEM imaging confirmed the existence of wire-type structures. Wire structures and gelation were also observed for aqueous dispersions of pristine BBL. BBL-PNIPAM block-copolymers were found to be indispersible in water with PNIPAM fractions lower than 35 mass %. However, they gelled upon ultrasonication. With higher PNIPAM fractions the polymers were dispersible and did not form gels in any of the studied concentrations. Dispersibility in water and the colloidal stability of BBL-PEOs and BBL-PNIPAMs was attributed to electrostatic stabilization as the particles showed negative zeta-potentials. Dispersible BBL-PNIPAMs were more stable due the high amount of dissociative groups originating from the partial degradation of the amide moieties during the coupling to BBL. One of the monomers used to prepare BBL, 1,4,5,8-naphthalenetetracarboxylic acid 1,8-monoanhydride, was successfully mono- and dibrominated. The bromine was then used as a functional group and replaced either directly with 2-ethyl-1-hexylamine or substituted with azide and reacted with 1-hexyne. The modified monomers were used in preparation of BBL. BBLs bearing either 2-ethyl-1-hexylamine or 4-butyl-1,2,3-triazole groups were found to be sparingly soluble in dimethylsulphoxide and N-methyl-2-pyrrolidone.
  • Salmi, Emma (Helsingin yliopisto, 2015)
    Corrosion is a major global challenge with both economical and technological impacts. The total world-wide costs of corrosion have been evaluated to rise to over 2 000 000 million euros annually. While several methods exist for corrosion protection, atomic layer deposited (ALD) coatings have an advantage in applications where thin, fully conformal, highly precise and well-defined coatings both in composition and thickness are needed. In this work the corrosion protection properties of ALD Al2O3 and Ta2O5 based coatings on low alloy steel were studied. The aim was to increase the general understanding on factors affecting the protective properties and failure mechanisms of the ALD coatings. The protective performance of ALD coatings on steel was improved by focusing on three topics: substrate pre-treatment, optimisation of the ALD coating architecture, and combination of the optimised ALD coatings with layers deposited by other methods. The substrate surface was found to significantly influence the ALD coating performance. Improved protective properties were found on steel samples that were mechanically polished to a lower surface roughness, and efficiently cleaned with H2-Ar plasma in addition to the traditional degreasing with an organic solvent. The smoother surface finish was concluded to be beneficial due to decreased defect formation after the coating deposition upon detachment of loose particles or mechanically fragile sites. The H2-Ar plasma removed organic residues from the steel surface, therefore improving the quality of the first layers of the ALD coating. The performance of the ALD coatings themselves was found to improve when Al2O3 and Ta2O5 were combined to produce Al2O3-Ta2O5 nanolaminate and AlxTayOz mixture coatings. In these coatings Al2O3 provided sealing properties and Ta2O5 the chemical stability, therefore resulting in coatings with better long-term performance than could be achieved with either material alone. Optimisation of the Al2O3-Ta2O5 nanolaminate and AlxTayOz mixture coating architectures further enhanced the protective properties. To further improve the coating-steel interface and to widen the application areas for the ALD based protective coatings, the optimised ALD coating processes were combined with layers deposited with other methods. Firstly, thin filtered cathodic arc sublayers were used to separate the ALD process from the steel surface. This enabled a more precise control of the coating-steel interface and led to improved durability of the ALD coatings. Secondly, pinhole defects in physical vapour and plasma-enhanced chemical vapour deposited hard coatings were sealed with ALD to afford coatings with both good corrosion protection performance and resistance against mechanical wear.
  • Ridderstad, Marianna (Helsingin yliopisto, 2015)
    Studies of ancient monuments and buildings have shown that many of them were astronomically oriented. The examination of the orientations of the structures constructed by past cultures can thus reveal previously unknown details of their astronomical knowledge, calendric practices and religious beliefs. In this thesis, the orientations of two types of structures from prehistoric and early historical Finland were investigated: the Giants Churches (GCs), which are large Neolithic (ca. 1800-3000 BCE) stone enclosures situated mainly on the ancient coast of Ostrobothnia, and the medieval stone churches of Finland (ca. 1300-1550 CE). The results of the studies showed that the axes and gates of the GCs pointed towards the directions of certain solar and lunar events, possibly even indicating the existence of a lunar or lunisolar seasonal pointer calendric system of the type that has been previously suggested for European Neolithic monuments. The small GCs were oriented differently from the large ones, and especially the very largest GCs had orientations towards some of the main solar events of the year. The studies also revealed that the GCs were positioned to face open views towards the eastern and south-eastern horizon, and that the cairns around them were often symmetrically placed with respect to each other and the enclosures of the GCs. The orientations of the stone churches were found to have been mainly towards the sunrises of the equinoxes as given by the various possible definitions of the equinox in medieval times. Part of the orientation distribution could also be related to the sunrises of the Easter Day, and some individual churches may have been targeted towards the sunrises of the feast days of their patron saints. Comparison of the monument orientations from the two very different periods of time and cultures, the Neolithic GC culture and the medieval Finland showed that while there were many similarities in the orientations themselves, the interpretations made of the orientations and their possible related belief systems necessarily have differences. Also, the uncertainties in the interpretations of the orientations of a distant illiterate culture, in this case the Neolithic GC culture, persist. The concrete use of pre-Christian myths in rituals at the time when the medieval Christian churches were at use illustrates the complexity of the situation of the vernacular religion in Finland in historical times. This complexity naturally has an effect on the interpretations made on how the medieval Finnish parish members may have interpreted the observed orientations of the stone churches. Thus, also the interpretations made of the meanings of the orientations in a literate culture relatively close in time, where one has written sources preserved, may bear uncertainties due to the complex situation of the vernacular religious practices and beliefs. The complexity of the religious situation and the related interpretations of the church orientations in medieval Finland indicate the existence of limitations on how the orientations of the Neolithic structures, which are much more distant in time and culture, can and should be interpreted.
  • Al-Hunaiti, Afnan (Helsingin yliopisto, 2015)
    The catalytic oxidation by using transition metal complexes offers attractive opportunities for industrial applications following environmentally benign manufacturing processes. However, the number of such catalytic methods has substantially decreased. In this thesis, we developed and utilized three iron based catalysts (FeIII/thymine-1-acetic acid, FeIII/Phenanthroline, and FeII/Nmethylimidazole) and one organic catalysts (1,2-Di(1-naphthyl)-1,2-ethanediamine (NEDA)). The iron/THA catalyst (iron/thymine-1-acetic acid) is efficiently capable of oxidizing both primary and secondary aliphatic alcohols into their corresponding carbonyl compounds, acids and ketones. The system can also oxidize alkanes with different steric and electronic environment. We also presented a new method for the oxidation of benzylic and aliphatic primary and secondary alcohols using iron-based catalyst, which is [Fe(phen)2Cl2]NO3 (iron/Phenanthroline), with hydrogen peroxide as a terminal oxidant. The easily accessible catalyst (iron/N-methylimidazole) was developed to form dehydrogenative coupling reaction between benzaldehydes and styrenes. The CH activation to produce α,β unsaturated ketones has been also developed. The organic (metal-free) catalyst (1,2-Di(1-naphthyl)-1,2-ethanediamine (NEDA)) has shown to be an efficient catalyst for the oxidation of secondary alcohols with t-BuOOH as a terminal oxidant. Under mild reaction conditions, a secondary alcohol is converted into its corresponding ketone.
  • Sahlstedt, Elina (Helsingin yliopisto, 2015)
    Fluid evolution in fractured bedrock at the Olkiluoto site in Finland was investigated by examining the stable oxygen and carbon isotope composition of secondary calcite and sulfur isotope composition of secondary sulfide minerals. The study site, located on the western coast of Finland, is the planned site for the geological disposal of spent nuclear fuel. Therefore, hydrogeochemical conditions in the deep bedrock are of special interest. The aim of this study was to characterize the latest fracture fillings and use the isotope composition of these fillings as a proxy of past geochemical conditions. In addition to traditional stable isotope analyses, sulfur and carbon isotope variations in the samples were analysed in situ using secondary ion mass spectrometry (SIMS). The results demonstrated a high variability in isotopic composition of mineral grains within a few tens of micrometers. The study material consists of drill core sections hosting fracture infills, obtained from water conducting fractures in hydrologically active zones in the bedrock. Fracture filling calcites were grouped into five groups according to calcite morphology, mineral associations and their relative position in the fracture sequence. The latest fracture fillings were identified from the surfaces of open fractures as clear, platy or euhedral fillings (Group 1) which occasionally contained minor amount of silicate inclusions (Group 2). Massive, older calcite fillings were separated into three groups (Groups 3-5) representing high temperature fluid circulation. Group 3 fillings preceded the late-stage calcite fillings and are interpreted to be associated with a Paleozoic (541-252 Ma) thermal event. Group 5 and Group 4 fillings represent the earliest hydrothermal events in the bedrock, likely related to the rapakivi granite and diabase intrusions of Mesoproterozoic (1600-1000 Ma) age. A characteristic feature of the late-stage fillings (Group 1, 2) is small-scale variations in stable isotope compositions, indicating the influence of microbial processes on groundwater conditions. Furthermore, a comparison with the groundwater data showed that the late-stage fillings are generally not in isotopic equilibrium with the current groundwaters. Based on the results obtained in this work, the following characteristics of the paleogroundwaters representing Group 1-2 mineralizations can be identified: Transitions between geochemically distinct environments can be identified in the shallow bedrock, at depths < 100 m. The upper ca. 30 m were characterized by bacterial sulfate reduction (BSR) and depths < 54 m characterized by methanogenetic activity. A narrow zone existed at the depths of ~34-54 m, where BSR was accompanied by minor methanotrophic activity. After the precipitation of calcite in Groups 1-2, the methanic environment in the depth range of ~60-300 m has been replaced by sulfidic conditions. Changes to this environment were most likely associated with the infiltration events related to deglaciation events and glacioisostatic land movements, which have occurred repeatedly during the Quaternary period (< 2.58 Ma).
  • Koivisto, Juha (Helsingin yliopisto, 2015)
    The growing number of x-ray examinations being routinely performed on patients using cone-beam computed tomography (CBCT) and multi-slice computed tomography (MSCT) devices have led to an emerging risk of and concern about radiation exposure. Typical CBCT absorbed doses range between 1 7 mGy, and thus values less than 1 mGy can be considered as low dose values. To date, most studies concerning effective dose assessment in the maxillofacial region use anthropomorphic phantoms in combination with thermoluminescent dosimeters (TLD). Recently, MOSFET dosimeters have been considered as a possible alternative to TLDs for in vitro dose assessment. The major benefit of MOSFET dosimeters is their real-time dose measurement capabilities. All 20 MOSFET dosimeters were characterized for CBCT photon energy ranges, dose properties, and organ dose measurements using TLD dosimeters (I). The MOSFET dosimeter energy dependencies were evaluated for two photon energy ranges in order to encompass the typical mean photon energies used in dental radiology. Furthermore, the MOSFET dosimeter uncertainty was assessed by repetitive measurements at different doses. The MOSFET angular sensitivity was investigated using dental photon energies and soft tissue equivalent backscatter material. After MOSFET characterization, a dose measurement setup was developed. The setup comprised 20 MOSFET dosimeters that were placed into the allocated grid holes of an anthropomorphic RANDO phantom. The MOSFET dose measurement setup was validated using two different methods: Monte Carlo simulations and TLD dosimeters. The setup was used for organ and effective dose assessments resulting from supine, prone, and oblique phantom positions in the maxillofacial region using a novel cone beam computed tomography (CBCT) device and from two conventional dental CBCTs and one multi-slice computed tomography (MSCT) device. All MOSFET dosimeters demonstrated a statistically insignificant energy dependency when using typical dental photon energies. Furthermore, the MOSFETs demonstrated excellent dose linearity and resulted in similar absorbed organ doses to those attained in the TLD measurements. The required low dose limit was achieved by averaging the values attained using eight MOSFET exposures. The MOSFET dosimeter angular dependency demonstrated a 5% standard deviation from the mean sensitivity value. The MOSFET dose assessment setup demonstrated similar effective doses to those attained using the Monte Carlo simulations and TLD measurements. Effective dose was strongly dependent on the vertical phantom positioning and minor vertical changes resulted in dose increases of up to 16%. The dose measurements acquired using the same FOV on all CBCT and MSCT devices 3 resulted in the following values: Planmed Verity CBCT scanner 247 μSv in supine, 192 μSv in prone, and 134 μSv in oblique position, the ProMax 3D MAX CBCT 168 μSv, i-CAT Next Generation 170 μSv, Philips Brilliance 64 MSCT 781 μSv. The results of this study demonstrate that the mean photon energy dose dependency corrections are not required in typical dental energy ranges. Furthermore, averaging eight MOSFET exposures attained typical TLD low dose values. Due to their variation in angular sensitivity, MOSFET dosimeters should always be calibrated in clinical settings for beam geometry and the angular range of the CBCT exposure. Based on the results of the Monte Carlo simulations and TLD measurements, the MOSFET measurement setup constitutes a feasible method for low dose assessment in CBCT and MSCT devices in the maxillofacial region. When using the same FOV and exposure parameters, the effective doses obtained in the supine position were 29% higher (247 μSv) than those obtained in the prone position (192 μSv). When the prone and oblique positions were compared, the observed effective dose in the oblique position was 30% lower. Thus, optimal patient positioning can reduce the dose and subsequently minimize the radiation risks. In summary, the fast and dependable low- dose measurement setup presented in this thesis provides an effective means of CBCT dose assessment using a variety of exposure parameters, patient positioning, and FOVs. Further, the setup presented in this study can be used to test and develop CBCT devices that would subsequently produce lower effective doses. Since radiologists commonly only have access to the radiation output of different devices, they lack the possibility to assess the actual effective dose. Therefore, the setup developed in this thesis can also be utilized to increase the awareness of the lifetime radiation risks amongst radiologists leading to dose reduction
  • Lusa, Merja (Helsingin yliopisto, 2015)
    129I, 79Se and 135Cs are among the most important radionuclides in the biosphere safety assessments of the disposal of spent nuclear fuel. The sorption, retention and migration of these nuclides in the surface environment is of importance when the radiation doses for humans and other organisms in the future is considered. In this doctoral thesis the abiotic and biotic factors affecting the retention of iodide (I-), selenite (SeO32-) and cesium (Cs+) in a nutrient-poor boreal bog environment were investigated. Batch sorption experiments were used both for the bog layer samples from the surface moss, subsurface peat, gyttja and clay layers of the bog and for bacteria isolated from the bog. The bacteria isolates belonged to four different phyla: Pseudomonas, Rhodococcus, Burkholderia and Paenibacillus commonly found in the various environments. I- and SeO32- retention in the surface moss, peat, gyttja and clay was found to be strongly linked to the microbial activity found in this bog. Sterilization of the surface moss, peat, gyttja and clay samples significantly reduced the retention of both I- and SeO32- and anoxic conditions reduced the sorption of I-. These results supported the hypothesis that viable microbiota (bacteria/fungi) are necessary for the incorporation of I- into the organic matter and for the retention of SeO32- through microbiotically mediated reduction in the acidic bog environment and that I- is oxidized into I2 and/or HIO prior to its incorporation into the organic matter. In the case of SeO32- the removal from the solution phase presumably takes place via reduction of SeO32- into insoluble Se0 (and possible further reduction to Se2-, which reacts with iron). Some proportion of abiotic reduction of SeO32- in association with sulfide oxidation is possible, but the majority of the reduction is assumed to occur microbiotically. This is supported by the observation that SeO32- removal from the solution was at the same level both under oxic and anoxic conditions, but was decreased as samples were sterilized and incubated under oxic conditions. In addition the bacteria isolated from the bog were found to remove both I- and SeO32- from the solution, although the removal was considerably higher for SeO32-. The behaviour of Cs+ was affected by both abiotic and biotic factors (i.e. pH, clay minerals and bacteria) in the acidic nutrient-poor boreal bog investigated in this thesis. Increase in the pH, increased the sorption of Cs+ in all studied bog layers and highest sorption was observed in the bottom layer of the bog. In this layer, clay minerals, especially illite, were found. Sterilization of the samples decreased the sorption of Cs+, but the difference between sterilized and unsterilized samples was not statistically significant. However the bacteria isolated from the bog were found to remove Cs+ from the solution, though the extend of the removal was significantly lower than that observed for SeO32-. In addition implications on the importance of plant uptake and rhizoidosphere effects of Sphagnum moss on the Cs+ retention in the surface layer of the bog were observed.
  • Avchaciov, Konstantin (2015)
    Rapid technological development motivates the research community to find out new processing technologies for producing materials with unique properties. Production of new materials or improving the existing ones requires development of new methods, which sometimes involves processing under far-from-equilibrium conditions. Usually underlying physical processes, taking place during such processing, are not well known. Understanding them is the key to the enhancement of processing methods. This thesis covers only a tiny part of a huge number of problems existing in the material science. The studies done here could be useful for solving the problem of metallic glass brittleness and for further development of the ion beam technology for controlling magnetic properties of thin films. Discussion on the pathway of the self-propagating high-temperature synthesis in multilayer metallic films was also included in the thesis We studied the effect of ion irradiation on Cu64Zr36 metallic glass by means of molecular dynamics (MD). Low-energy ion irradiation of metallic glass produces damage zones, where the local structure of glass differs from the structure of pristine glass. These changes are independent on ion energy and flux due to the possibility of partial recovery during cascade relaxation. However, the size of the damage zones could be controlled by varying the dose of ions. This makes possible the production of either isolated damaged regions or homogeneously damaged glass. We showed that mechanical properties of the glass strongly depend on the local structure. In damage zones, the specific arrangement of the structural units is destroyed. This promotes the formation of many shear transformation zones in the damaged area, when a mechanical load is applied. It results in enhanced plasticity of the irradiated glass. Our research indicates that ion irradiation could be used for the softening of brittle metallic glasses for preventing formation of cracks in them. Atomistic studies of the reaction pathway in the multilayer Ru/Al films were done to interpret the results from X-ray diffraction measurements. The MD simulations covered the first nanoseconds; at this timescale, no information about the reaction pathway could be obtained from the experimental methods. The MD simulations demonstrated simultaneous Ru dissolution into liquid Al and $B2$ RuAl phase nucleation at the Ru/Al interface. Our results agreed well with experimental observations, and, moreover, helped to refine understanding of the X-Ray diffractograms. We also studied structural modifications of Pt/Co/Pt trilayer films, which could explain appearance of the perpendicular magnetic anisotropy (PMA) after irradiation with Ga+ ions. Molecular dynamics and Monte Carlo (MD-MC) simulations were performed to find changes in the long range order and short range order, associated with ion irradiation. The results of our simulations showed that the separated metal layers containing Pt and Co were intermixed and formed the new solid solution. This solution was chemically disordered at the nanosecond time scale. With combined MD-MC simulations, we showed that the transition between chemically ordered and disordered phases was possible. The fractions of the ordered phases grew monotonously with an ion dose due to the ongoing process of ion-beam mixing. However, assuming the correlation between the magnetic properties of the film and the fraction of the chemically ordered CoPt phase in it, this result cannot explain the disappearance of PMA at the high doses. The strain analysis showed that the Co layer exhibited tensile strain in the lateral direction at the moderate doses, where the PMA was detected. We explained the appearance of strains by changing of the thickness of the hcp-Co layer right inside the trilayer Pt/Co/Pt structure, which was possible due to its partial transformation to the fcc structure. Below the critical size of the hcp layer, the strain inside it appears, which, in our opinion, could cause the appearance of PMA at the moderate doses and the disappearance of PMA at the high doses.
  • Mäkelä, Minja (Helsingin yliopisto, 2015)
    The focus of this thesis is on observations of star-forming globules that have cometary morphologies and are associated with or located in HII regions. Our study presents a sample of globules at different size-scales and investigates their structure, formation mechanism, and star formation using observations made at infrared (IR) and millimeter (mm)-wave wavelengths. The studied globules offer examples of associated low-mass star formation triggered by the influence of an HII region. Infrared, mm, and radio observations are fundamental in detecting signs of on-going star formation embedded inside dusty, dense globules. The embedded young stellar objects (YSOs) are detected directly in the IR and indirectly via jets and outflows in shocked H2 and mm-wave CO observations. This thesis is a case study of different types of globules. Cometary globules (CGs) represent the classical globules with sizes of ~0.1-1 pc and masses of ~10 M_sun, and the so-called globulettes are an order of magnitude smaller than CGs. We observe on-going low-mass star formation in both types of globules. Compression associated with radiation from the hot central star (via so-called radiation driven implosion, RDI) is suggested as the cause. The star formation in the globulettes may result in low-mass stars and/or possibly in free-floating planetary-mass objects. Five publications are included, two of which discuss two cometary globules, CG 1 and CG 2, in the Gum Nebula. Earlier studies have discovered a pre-main sequence star outside the head of CG 1, and we find second generation star formation in the head of CG 1 which contains an embedded object and a large outflow cavity. Two near-IR (NIR)-excess objects are seen in the direction of CG 1 tail and one in the head of CG 2. Our original goal was to study if the CG formation mechanism is triggered by supernovae shocks or by RDI, but based on the observations, we cannot fully determine between the two. The next two papers discuss mm-wave and NIR observations of small globulettes in the Rosette Nebula. Globulettes have not been studied in the NIR before this. The globulettes are dense and they are irradiated by ultraviolet radiation from the central Rosette cluster which causes bright fluorescent H2 rims in the globulettes in the NIR. The globulettes are observed along with long pillars of gas extending toward the central cluster, so-called elephant trunks. These together form a system that expands at the same velocity from the central cluster. Star formation is on-going in the largest Rosette globulette observed in this study and in the tip of one elephant trunk. The final paper reports NIR observations of two globules on the inner molecular shell of the Rosette Nebula. They have fluorescent H2 rims similar to the globulettes. A NIR-excess object is located in the direction of one globule and the other contains an embedded YSO. The YSO drives an outflow seen in shocked H2. Imaging in the optical and NIR suggest that the outflow is parsec-scaled and interacts with the shell of the Rosette Nebula. The globules we observed are subject to ionizing radiation from OB stars, which photo-erodes the globules and drives the RDI process. Star formation takes place in all globule types we observed, and the second generation star in the head of CG 1 is indicative of triggered star formation. The first detailed NIR and mm-wave observations of the Rosette Nebula globulettes are presented here. Star formation is detected in one globulette and in one of the associated elephant trunks, but we cannot determine if the globulettes can collapse to directly form brown dwarfs or planetary-mass objects. Future observations using ALMA and other high-resolution instruments are needed in determining the physical and chemical structure of the globulettes.
  • Numminen, Elina (Helsingin yliopisto, 2015)
    A central goal in science is to learn from observations about the process that generated the observations. The principles of statistical inference describe a systematic approach for such learning, in which prior information, knowledge about the underlying mechanisms and the observed data can be combined. In practice, lack of mathematical tractability, huge amounts of missing information, and the sensitivity of the conclusions on the assumptions made represent genuine challenges in the theoretically sound statistical framework. Statistical studies on the dynamics of infectious diseases easily face all these problems at once. In the thesis we present case-studies in which the datasets on bacterial diversity, mostly on Streptococcus pneumoniae, described in terms of either genotypes or serotypic strains, are analysed. By utilizing the machinery of modern computational statistics different strategies for inference are formulated, which aim to take the special characteristics of each of the studied problem into account, while overcoming the previously mentioned challenges in computational studies. For instance, an approximate Bayesian computation scheme is formulated for analysing cross-sectional strain prevalence data and an importance sampling scheme for analysing transmission trees with a priori known complex features. The obtained results unravel the mechanisms of seasonality in pneumococcal carriage, consequences of the host population structure and the nature of within-host competition between the bacterial strains.