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  • Hannula, Miika (Helsingin yliopisto, 2015)
    Dependence logic is a novel logical formalism that has connections to database theory, statistics, linguistics, social choice theory, and physics. Its aim is to provide a systematic and mathematically rigorous tool for studying notions of dependence and independence in different areas. Recently many variants of dependence logic have been studied in the contexts of first-order, modal, and propositional logic. In this thesis we examine independence and inclusion logic that are variants of dependence logic extending first-order logic with so-called independence or inclusion atoms, respectively. The work consists of two parts in which we study either axiomatizability or expressivity hierarchies regarding these logics. In the first part we examine whether there exist some natural parameters of independence and inclusion logic that give rise to infinite expressivity or complexity hierarchies. Two main parameters are considered. These are arity of a dependency atom and number of universal quantifiers. We show that for both logics, the notion of arity gives rise to strict expressivity hierarchies. With respect to number of universal quantifiers however, strictness or collapse of the corresponding hierarchies turns out to be relative to the choice of semantics. In the second part we turn attention to axiomatizations. Due to their complexity, dependence and independence logic cannot have a complete recursively enumerable axiomatization. Hence, restricting attention to partial solutions, we first axiomatize all first-order consequences of independence logic sentences, thus extending an analogous result for dependence logic. We also consider the class of independence and inclusion atoms, and show that it can be axiomatized using implicit existential quantification. For relational databases this implies a sound and complete axiomatization of embedded multivalued and inclusion dependencies taken together. Lastly, we consider keys together with so-called pure independence atoms and prove both positive and negative results regarding their finite axiomatizability.
  • Nikitin, Timur (Helsingin yliopisto, 2013)
    Silicon nanocrystals (Si-nc) embedded in a SiO₂ matrix is a promising system for silicon-based photonics. We studied optical and structural properties of Si-rich silicon oxide SiOₓ (x < 2) films annealed in a furnace at temperatures up to 1200 °C and containing Si-nc. The measured optical properties of SiOₓ films are compared with the values estimated by using the effective medium approximation and X-ray photoelectron spectroscopy (XPS) results. A good agreement is found between the measured and calculated refractive index. The results for absorption suggest high transparency of nanoscale suboxide. The extinction coefficient for elemental Si is found to be between the values for crystalline and amorphous Si. Thermal annealing increases the degree of Si crystallization; however, the Si–SiO₂ phase separation is not complete after annealing at 1200 °C. The 1.5-eV photoluminescence probably originates from small (~1 nm) oxidized Si grains or oxygen-related defects, but not from Si-nc with sizes of about 4 nm. The SiOx films prepared by molecular beam deposition and ion implantation are structurally and optically very different after preparation but become similar after annealing at ~1100 °C. The laser-induced thermal effects found for SiOₓ films on silica substrates illuminated by focused laser light should be taken into account in optical measurements. Continuous-wave laser irradiation can produce very high temperatures in free-standing SiOₓ and Si/SiO₂ superlattice films, which changes their structure and optical properties. The center of a laser-annealed area is very transparent and consists of amorphous SiO₂. Large Si-nc (up to 300 nm) are observed in the ring around the central region. These Si-nc produce high absorption and they are typically under compressive stress, which is connected with the crystallization from the melt phase. Some of the large Si-nc exhibit surface features, which is interpreted in terms of eruption of pressurized Si from the film. A part of large Si-nc is removed from the film forming holes of similar sizes. The presence of oxygen in the laser-annealing atmosphere decreases the amount of removed Si-nc. The structure of laser-annealed areas is explained by thermodiffusion, which leads to the macroscopic Si–SiO₂ phase separation. Comparison of the structure of central regions for laser annealing in oxygen, air, and inert atmospheres excludes the dominating effect of Si oxidation in the formation of laser-annealed area. By using a strongly focused laser beam, the structural changes in the free-standing films can be obtained in submicron areas, which suggests a concept of nonvolatile optical memory with high information density and superior thermal stability.
  • Backman, John (Helsingin yliopisto, 2015)
    Aerosol particles are part of the Earth's climatic system. Aerosol particles can significantly impact the climate. The ability of aerosol particles to do so depends mainly on the size, concentration and chemical composition of the particles. Aerosol particles can act as cloud condensation nuclei (CCN) and can therefore mediate cloud properties. Aerosol particles can thus perturb the energy balance of the Earth through clouds. Aerosol particles can also directly interact with solar radiation through scattering, absorption, or both. The climatic implications of aerosol radiation interactions depend on the Earth s surface properties and the amount of light scattering in relation to light absorption. Light absorbing aerosol particles, in particular, can alter the vertical temperature structure of the atmosphere and inhibit the formation of convective clouds. The net change in the energy balance imposed by perturbing agents, such as aerosol particles, results in a radiative forcing. Globally, aerosol particles have a net cooling effect on the climate, but, not necessarily on a local scale. Accurate measurements of the optical properties of aerosol particles are needed to estimate the climatic effects of aerosols. A widely used means of measuring light absorption by aerosol particles is to use a filter-based measurement technique. The technique is based on light-transmission measurements through the filter when the aerosol sample is drawn through the filter and particles deposit onto the filter. As the sample deposits, it will inevitably interact with the fibres of the filter and the interactions needs to be taken into account. This thesis investigates different approaches to dealing with filter-induced artefacts and how they affect aerosol light absorption using this technique. In addition, the articles included in the thesis report aerosol optical properties at sites that have not been reported in the literature before. The locations range from an urban environment in the city of São Paulo, Brazil, an industrialised region of the South African Highveld, to a rural station in Hyytiälä in Finland. In general, it can be said that sites that are distant from urban areas tend to scatter more light in relation to light absorption. In urban areas, the aerosol particle optical properties show the aerosol particles to be darker.
  • Rasmus, Kai (Helsingin yliopisto, 2009)
    The Antarctic system comprises of the continent itself, Antarctica, and the ocean surrounding it, the Southern Ocean. The system has an important part in the global climate due to its size, its high latitude location and the negative radiation balance of its large ice sheets. Antarctica has also been in focus for several decades due to increased ultraviolet (UV) levels caused by stratospheric ozone depletion, and the disintegration of its ice shelves. In this study, measurements were made during three Austral summers to study the optical properties of the Antarctic system and to produce radiation information for additional modeling studies. These are related to specific phenomena found in the system. During the summer of 1997-1998, measurements of beam absorption and beam attenuation coefficients, and downwelling and upwelling irradiance were made in the Southern Ocean along a S-N transect at 6°E. The attenuation of photosynthetically active radiation (PAR) was calculated and used together with hydrographic measurements to judge whether the phytoplankton in the investigated areas of the Southern Ocean are light limited. By using the Kirk formula the diffuse attenuation coefficient was linked to the absorption and scattering coefficients. The diffuse attenuation coefficients (Kpar) for PAR were found to vary between 0.03 and 0.09 1/m. Using the values for KPAR and the definition of the Sverdrup critical depth, the studied Southern Ocean plankton systems were found not to be light limited. Variabilities in the spectral and total albedo of snow were studied in the Queen Maud Land region of Antarctica during the summers of 1999-2000 and 2000-2001. The measurement areas were the vicinity of the South African Antarctic research station SANAE 4, and a traverse near the Finnish Antarctic research station Aboa. The midday mean total albedos for snow were between 0.83, for clear skies, and 0.86, for overcast skies, at Aboa and between 0.81 and 0.83 for SANAE 4. The mean spectral albedo levels at Aboa and SANAE 4 were very close to each other. The variations in the spectral albedos were due more to differences in ambient conditions than variations in snow properties. A Monte-Carlo model was developed to study the spectral albedo and to develop a novel nondestructive method to measure the diffuse attenuation coefficient of snow. The method was based on the decay of upwelling radiation moving horizontally away from a source of downwelling light. This was assumed to have a relation to the diffuse attenuation coefficient. In the model, the attenuation coefficient obtained from the upwelling irradiance was higher than that obtained using vertical profiles of downwelling irradiance. The model results were compared to field measurements made on dry snow in Finnish Lapland and they correlated reasonably well. Low-elevation (below 1000 m) blue-ice areas may experience substantial melt-freeze cycles due to absorbed solar radiation and the small heat conductivity in the ice. A two-dimensional (x-z) model has been developed to simulate the formation and water circulation in the subsurface ponds. The model results show that for a physically reasonable parameter set the formation of liquid water within the ice can be reproduced. The results however are sensitive to the chosen parameter values, and their exact values are not well known. Vertical convection and a weak overturning circulation is generated stratifying the fluid and transporting warmer water downward, thereby causing additional melting at the base of the pond. In a 50-year integration, a global warming scenario mimicked by a decadal scale increase of 3 degrees per 100 years in air temperature, leads to a general increase in subsurface water volume. The ice did not disintegrate due to the air temperature increase after the 50 year integration.
  • Wallin, Anders (Helsingin yliopisto, 2011)
    Molecular machinery on the micro-scale, believed to be the fundamental building blocks of life, involve forces of 1-100 pN and movements of nanometers to micrometers. Micromechanical single-molecule experiments seek to understand the physics of nucleic acids, molecular motors, and other biological systems through direct measurement of forces and displacements. Optical tweezers are a popular choice among several complementary techniques for sensitive force-spectroscopy in the field of single molecule biology. The main objective of this thesis was to design and construct an optical tweezers instrument capable of investigating the physics of molecular motors and mechanisms of protein/nucleic-acid interactions on the single-molecule level. A double-trap optical tweezers instrument incorporating acousto-optic trap-steering, two independent detection channels, and a real-time digital controller was built. A numerical simulation and a theoretical study was performed to assess the signal-to-noise ratio in a constant-force molecular motor stepping experiment. Real-time feedback control of optical tweezers was explored in three studies. Position-clamping was implemented and compared to theoretical models using both proportional and predictive control. A force-clamp was implemented and tested with a DNA-tether in presence of the enzyme lambda exonuclease. The results of the study indicate that the presented models describing signal-to-noise ratio in constant-force experiments and feedback control experiments in optical tweezers agree well with experimental data. The effective trap stiffness can be increased by an order of magnitude using the presented position-clamping method. The force-clamp can be used for constant-force experiments, and the results from a proof-of-principle experiment, in which the enzyme lambda exonuclease converts double-stranded DNA to single-stranded DNA, agree with previous research. The main objective of the thesis was thus achieved. The developed instrument and presented results on feedback control serve as a stepping stone for future contributions to the growing field of single molecule biology.
  • Suomela, Jukka (Helsingin yliopisto, 2009)
    This thesis studies optimisation problems related to modern large-scale distributed systems, such as wireless sensor networks and wireless ad-hoc networks. The concrete tasks that we use as motivating examples are the following: (i) maximising the lifetime of a battery-powered wireless sensor network, (ii) maximising the capacity of a wireless communication network, and (iii) minimising the number of sensors in a surveillance application. A sensor node consumes energy both when it is transmitting or forwarding data, and when it is performing measurements. Hence task (i), lifetime maximisation, can be approached from two different perspectives. First, we can seek for optimal data flows that make the most out of the energy resources available in the network; such optimisation problems are examples of so-called max-min linear programs. Second, we can conserve energy by putting redundant sensors into sleep mode; we arrive at the sleep scheduling problem, in which the objective is to find an optimal schedule that determines when each sensor node is asleep and when it is awake. In a wireless network simultaneous radio transmissions may interfere with each other. Task (ii), capacity maximisation, therefore gives rise to another scheduling problem, the activity scheduling problem, in which the objective is to find a minimum-length conflict-free schedule that satisfies the data transmission requirements of all wireless communication links. Task (iii), minimising the number of sensors, is related to the classical graph problem of finding a minimum dominating set. However, if we are not only interested in detecting an intruder but also locating the intruder, it is not sufficient to solve the dominating set problem; formulations such as minimum-size identifying codes and locating dominating codes are more appropriate. This thesis presents approximation algorithms for each of these optimisation problems, i.e., for max-min linear programs, sleep scheduling, activity scheduling, identifying codes, and locating dominating codes. Two complementary approaches are taken. The main focus is on local algorithms, which are constant-time distributed algorithms. The contributions include local approximation algorithms for max-min linear programs, sleep scheduling, and activity scheduling. In the case of max-min linear programs, tight upper and lower bounds are proved for the best possible approximation ratio that can be achieved by any local algorithm. The second approach is the study of centralised polynomial-time algorithms in local graphs these are geometric graphs whose structure exhibits spatial locality. Among other contributions, it is shown that while identifying codes and locating dominating codes are hard to approximate in general graphs, they admit a polynomial-time approximation scheme in local graphs.
  • Lindström, Jan (Helsingin yliopisto, 2003)
  • Kaasalainen, Touko (Helsingin yliopisto, 2015)
    The number of computed tomography (CT) examinations has increased in recent years due to developments in scanner technology and the increased diagnostic capabilities of CT. Nowadays, CT has become a major contributor to accumulated radiation doses from radiological examinations, accounting for approximately 60% of the overall medical radiation dose in Western countries. Ionizing radiation is generally considered harmful to health, and current knowledge suggests that the risk for stochastic effects increases linearly with radiation dose. Minimizing patient doses in CT requires effective optimization practices, including both technical and clinical approaches. CT optimization aims to reduce patients exposure to radiation without compromising image quality for diagnosis. The aim of this dissertation was to explore the feasibility of using anthropomorphic phantoms and metal-oxide-semiconductor field-effect transistors (MOSFETs) in CT optimization and patient dose measurements, and to study CT optimization in versatile clinical situations. Specifically, this thesis focused on studying the effects of patient centering on the CT scanner isocenter by determining changes in patient dose and image quality. Additionally, as a part of this thesis, we constructed and optimized ultralow-dose CT protocols for craniosynostosis imaging, and explored different optimization methods for reducing radiation exposure to eye lenses. Moreover, fetal radiation doses were assessed in the most typical CT examinations of a pregnant woman which also place the fetus at the highest risk for ionizing radiation-induced health detriments. Anthropomorphic phantoms and MOSFET dosimeters proved feasible in CT optimization even with the use of ultralow-dose levels. Patient vertical off-centering posed a common and serious problem in chest CT, as a majority of the scanned patients were positioned below the isocenter of the CT scanner, which significantly affected both radiation dose and image quality. This exposes the radiosensitive anterior surface tissues, including the breasts and thyroid gland, to greater risk. Special attention should focus on pediatric patients in particular, as they were typically miscentered lower than adults were. The use of constructed ultralow-dose CT protocols with model-based iterative reconstruction can enable craniosynostosis CT imaging with sufficient image quality for diagnosis with an effective dose of less than 20 μSv for the patient. This dose level was approximately 85% lower than the level used in routine CT protocols in the hospital for craniosynostosis, and was comparable to the radiation exposure of a plain-skull radiography examination. The most efficient method for reducing the dose to the eye lens proved to be gantry tilting, which leaves the eye lenses outside the primary radiation beam, thereby reducing the absorbed dose up to 75%. However, measurements with two different anthropomorphic head phantoms showed that patient geometry significantly affects dose-reduction capabilities. If lenses can only partially be cropped outside the primary beam, organ-based tube current modulation or bismuth shields may also be used for reducing the dose to the lenses. Based on the measured absorbed doses in this thesis, the radiation dose to the fetus poses no obstacle to an optimized CT examination with a medically necessary indication. The volumetric CT dose index (CTDIvol) provides a rough estimate of the fetal dose when the uterus is in the primary radiation beam, although the extent of the scan range has a substantial effect on the fetal dose. The results support the conception that when the fetus or uterus is not in the scan range, the fetal dose is affected mainly by the distance from the scan range.
  • Pikkarainen, Anna-Liisa (Helsingin yliopisto, 2008)
    The Baltic Sea was studied with respect to selected organic contaminants and their ecotoxicology. The research consisted of analyses of total hydrocarbons, polycyclic aromatic hydrocarbons, bile metabolites, hepatic ethoxyresorufin-O-deethylase (EROD) activity, polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs). The contaminants were measured from various matrices, such as seawater, sediment and biota. The methods of analysis were evaluated and refined to comparability of the results. Polyaromatic hydrocarbons, originating from petroleum, are known to be among the most harmful substances to the marine environment. In Baltic subsurface water, seasonal dependence of the total hydrocarbon concentrations (THCs) was seen. Although concentrations of parent polycyclic aromatic hydrocarbons (PAHs) in sediment surface varied between 64 and 5161 ug kg-1 (dw), concentrations above 860 ug kg-1 (dw) were found in all the studied sub-basins of the Baltic Sea. Concentrations commonly considered to substantially increase the risk of liver disease and reproductive impairment in fish, as well as potential effects on growth (above 1000 ug kg-1 dw), were found in all the studied sub-basins of the Baltic Sea except Kattegat. Thus, considerable pollution in sediments was indicated. In bivalves, the sums of 12 PAHs varied on a wet weight basis between 44 and 298 ug kg-1 (ww). The predominant PAHs were high molecular weight and the PAH profiles of M. balthica differed from those found in sediment from the same area. The PAHs were both pyrolytic and petrogenic in origin, and a contribution from diesel engines was found, which indicates pollution of the Baltic Sea, most likely caused by the steadily increasing shipping in the area. The HPLC methods developed for hepatic EROD activity and bile metabolite measurements proved to be fast and suitable for the study of biological effects. A mixed function oxygenase enzyme system in Baltic Sea perch collected from the Gulf of Finland was induced slightly: EROD activity in perch varied from 0.30 14 pmol min-1 mg-1 protein. This range can be considered to be comparable to background values. Recent PAH exposure was also indicated by enhanced levels (213 and 1149 ug kg-1) of the bile metabolite 1-hydroxypyrene. No correlation was indicated between hepatic EROD activity and concentration of 1-hydroxypyrene in bile. PCBs and OCPs were observed in Baltic Sea sediment, bivalves and herring. Sums of seven CBs in surface sediment (0 5 cm) ranged from 0.04 to 6.2 ug kg-1 (dw) and sums of three DDTs from 0.13 to 5.0 ug kg-1 (dw). The highest levels of contaminants were found in the most eastern area of the Gulf of Finland where the highest total carbon and nitrogen content was found and where the lowest percentage proportion of p,p -DDT was found. The highest concentrations of CBs and the lowest concentration of DDTs were found in M. balthica from the Gulf of Finland. The highest levels of DDTs were found in M. balthica from the Hanö Bight, which is the outer part of the Bornholm Basin close to the Swedish mainland. In bivalves, the sums of seven CBs were 72 108 ug kg-1 (lw) and the sums of three DDTs were 66 139 ug kg-1 (lw). Results from temporal trend monitoring showed, that during the period 1985 2002, the concentrations of seven CBs in two-year-old female Baltic herring were clearly decreased, from 9 16 to 2 6 ug kg-1 (ww) in the northern Baltic Sea. At the same time, concentrations of three DDTs declined from 8 15 to 1 5 ug kg-1 (ww). The total concentration of the fat-soluble CBs and DDTs in Baltic herring muscle was shown to be age-dependent; the average concentrations in ten-year-old Baltic herring were three to five-fold higher than in two-year-old herring. In Baltic herring and bivalves, as well as in surface sediments, CB 138 and CB153 were predominant among CBs, whereas among DDTs p,p'-DDD predominated in sediment and p,p'-DDE in bivalves and Baltic herring muscle. Baltic Sea sediments are potential sources of contaminants that may become available for bioaccumulation. Based on ecotoxicological assessment criteria, cause for concern regarding CBs in sediments was indicated for the Gulf of Finland and the northern Baltic Proper, and for the northern Baltic Sea regarding CBs in Baltic herring more than two years old. Statistical classification of selected organic contaminants indicated high-level contamination for p,p'-DDT, p,p'-DDD, p,p'-DDE, total DDTs, HCB, CB118 and CB153 in muscle of Baltic herring in age groups two to ten years; in contrast, concentrations of a-HCH and g-HCH were found to be moderate. The concentrations of DDTs and CBs in bivalves is sufficient to cause biological effects, and demonstrates that long-term biological effects are still possible in the case of DDTs in the Hanö Bight.
  • Nuopponen, Markus (Helsingin yliopisto, 2008)
    Controlled radical polymerization techniques, such as RAFT polymerization, are modern alternatives for preparing pre-designed polymers. In RAFT polymerization, chain length, molar mass distribution, microstructure (tacticity and sequencing), composition and functionality can be controlled. This allows the synthesis of a variety of novel polymer architectures, such as block and graft copolymers, stars, hybride materials and bioconjugates. The self-organization of synthetic preformed polymers into controllable nanostuctures is one of the most promising topics in the material science. However, the field of block copolymer self-assembly is still relatively young and current polymeric materials are structurally rather simple compared to biological materials. Thus, novel generations of polymer-based materials offer huge opportunities in material science. In this work, amphiphilic di- and triblock copolymers were synthesized by RAFT polymerization, and their organization into specific structures at nanoscale was studied. In all the block copolymer, one of the blocks was thermoresponsive poly(N-isopropylacrylamide). Thus, polymers and studied materials were temperature sensitive. In addition, control over tacticity in N-isopropylacrylamide polymerization was studied. The self-organization in aqueous solutions was strongly affected by the tacticity and the block sequence. Amphiphilic polymers formed various micellar structures in aqueous solutions. These micellar microcontainers have applications in controlled drug delivery. Amphiphiles have also applications as dispersants in coatings and cosmetics. In bulk, all the stable block copolymer morphologies were observed for triblock copolymers. Hydrogels of triblock copolymers can be used as thermoresponsive membrane materials. Polymers synthesized through the RAFT polymerization can be directly used in the synthesis of polymer grafted nanoparticles. Gold nanoparticles have attracted great interest due to the fact that gold is the most stable and inert noble metal possessing unique surface properties and good conductivity. It was shown that the association and optical properties of the gold nanoparticles grafted with smart polymers can be widely varied by pH and temperature. This type of gold nanoparticles have applications in diagnostics, sensors and cell imaging.
  • Mølgaard, Bjarke (Helsingin yliopisto, 2014)
    Epidemiological and toxicological studies have clearly shown that air pollution has adverse effects on human health. Exposure to air pollution mainly occurs in the urban and in the indoor environment. Fine particles form a diverse group of air pollutants, which is responsible for some of the health effects, and they originate from many outdoor and indoor sources. This thesis aims to support efforts for reduction of human exposure to fine particles by development and evaluation of an urban forecast model and by evaluation of an indoor aerosol model and of air cleaners. Measured particle number size distributions were utilised in all studies, and the urban studies additionally utilised meteorological data. The urban aerosol was investigated by using cluster analysis, and the urban particle number concentration forecast model was based on a regression model with an autoregressive structure on its error term. It was evaluated using particle number concentrations from five cities. The utility of a Multi-Compartment Size-resolved Indoor Aerosol Model (MC-SIAM) for estimating airflows in a building was evaluated by comparison with results from a tracer gas technique. The performance of five portable indoor air cleaners was evaluated by applying a simple aerosol model to data from chamber experiments. The urban concentration of particles smaller than 50 nm was found to depend on local sources, while for larger sizes distant sources may dominate the concentration. The forecast model was found to perform best for locations with a strong influence of local sources. The estimates obtained with the MC-SIAM of airflows between the indoors and outdoors were good for periods during which good agreement between the modelled and measured particle number size distributions was obtained. The indoor airflow estimates deviated somewhat due to a commonly used simplification. Portable air cleaners utilising fans and filters performed as expected, but an ion generator was ineffective for most particle sizes. The forecast model can give useful forecasts in its present form under certain conditions but further development is desired to make it more versatile. The MC-SIAM is a valuable tool for the study of indoor aerosols except in case of fluctuating airflows. Portable air cleaners are useful for improving indoor air quality, but not all models perform well.
  • Lahtinen, Petro (Helsingin yliopisto, 2005)
  • 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.
  • Pehrman, Reijo (Helsingin yliopisto, 2012)
    This doctoral thesis is focused on the radiation induced oxidative dissolution of spent nuclear fuel. UO2 is typically used as a model substance for spent nuclear fuel on the dissolution simulation experiments, but transuranium elements and fission products are expected to influence the redox chemistry involved. The dissolution behaviour of NpO2 and PuO2 in H2O2 solution without complexing agent was compared to UO2. Based on the measured rates, the dissolution of the actinides is not expected to be congruent, with Np and Pu release rates lower than the U release rate. The oxidative dissolution of PuO2 was found to be enhanced by the presence of Fe2+ in solution. This enhancement was attributed to hydroxyl radicals produced in the Fenton reaction between Fe2+ and radiolytically produced H2O2. The presence of solid UO2 pellet was found to prolong the lifetime of Fe2+ in solution, leading to further enhancement on the Pu dissolution. Fission product doping of UO2 was found to not have significant effect on the catalytic decomposition of H2O2. Fission product doping was however observed to hinder the reaction of UO2 with oxidants MnO4- and IrCl62-, and the effect of doping to decrease with increasing reduction potential of the oxidants. Uranyl peroxide solid phase formation on UO2 surface was observed to depend strongly on the peroxide concentration on the solution. In high peroxide concentrations oriented UO4∙nH2O crystals formed plate-like formations covering the whole surface, and with decreasing H2O2 concentration the crystals became unoriented and covered the UO2 surface only partially. In situ study showed the phase formation in high H2O2 concentration to take place in hours, and no intermediate phases were detected. Method development was performed on two areas: H2O2 measurement in small solution volumes down to nanomolar concentrations by chemiluminescence was tested and optimal parameters studied, and reference Raman spectra for studtite, schoepite, becquerelite and soddyite was measured.
  • Salminen, Johanna (Helsingin yliopisto, 2009)
    The importance of supercontinents in our understanding of the geological evolution of the planet Earth has been recently emphasized. The role of paleomagnetism in reconstructing lithospheric blocks in their ancient paleopositions is vital. Paleomagnetism is the only quantitative tool for providing ancient latitudes and azimuthal orientations of continents. It also yields information of content of the geomagnetic field in the past. In order to obtain a continuous record on the positions of continents, dated intrusive rocks are required in temporal progression. This is not always possible due to pulse-like occurrences of dykes. In this work we demonstrate that studies of meteorite impact-related rocks may fill some gaps in the paleomagnetic record. This dissertation is based on paleomagnetic and rock magnetic data obtained from samples of the Jänisjärvi impact structure (Russian Karelia, most recent 40Ar-39Ar age of 682 Ma), the Salla diabase dyke (North Finland, U-Pb 1122 Ma), the Valaam monzodioritic sill (Russian Karelia, U-Pb 1458 Ma), and the Vredefort impact structure (South Africa, 2023 Ma). The paleomagnetic study of Jänisjärvi samples was made in order to obtain a pole for Baltica, which lacks paleomagnetic data from 750 to ca. 600 Ma. The position of Baltica at ca. 700 Ma is relevant in order to verify whether the supercontinent Rodinia was already fragmented. The paleomagnetic study of the Salla dyke was conducted to examine the position of Baltica at the onset of supercontinent Rodinia's formation. The virtual geomagnetic pole (VGP) from Salla dyke provides hints that the Mesoproterozoic Baltica - Laurentia unity in the Hudsonland (Columbia, Nuna) supercontinent assembly may have lasted until 1.12 Ga. Moreover, the new VGP of Salla dyke provides new constraint on the timing of the rotation of Baltica relative to Laurentia (e.g. Gower et al., 1990). A paleomagnetic study of the Valaam sill was carried out in order to shed light into the question of existence of Baltica-Laurentia unity in the supercontinent Hudsonland. Combined with results from dyke complex of the Lake Ladoga region (Schehrbakova et al., 2008) a new robust paleomagnetic pole for Baltica is obtained. This pole places Baltica on a latitude of 10°. This low latitude location is supported also by Mesoproterozoic 1.5 1.3 Ga red-bed sedimentation (for example the Satakunta sandstone). The Vredefort impactite samples provide a well dated (2.02 Ga) pole for the Kaapvaal Craton. Rock magnetic data reveal unusually high Koenigsberger ratios (Q values) in all studied lithologies of the Vredefort dome. The high Q values are now first time also seen in samples from the Johannesburg Dome (ca. 120 km away) where there is no impact evidence. Thus, a direct causative link of high Q values to the Vredefort impact event can be ruled out.
  • Leikoski, Tuomo (Helsingin yliopisto, 2014)
    Formation of carbon carbon bonds constitutes the basis of synthetic organic chemistry. The growing demand of safer and environmentally friendlier processes, combined with continuing need for more efficient and selective reactions, has given challenges to industrial and fundamental academic research. The objective of this thesis was to develop novel ways to perform important carbon carbon bond-forming reactions on solid support. Of special focus were palladium- and copper-catalysed reactions of unsaturated amines. Polymer-bound propargylamine and allylamine were arylated successfully by the palladium-catalysed Sonogashira and Heck reaction, respectively. Additionally, allenes were produced in the Crabbé homologation of polymer-bound propargylamine, where copper acetylide is acting as an intermediate. All of these reactions would give rise to biologically interesting molecules: 1,3-arylaminopropanes after hydrogenation of the Sonogashira and Heck products and nitrogen-containing allenes by the Crabbé reaction. By varying the aryl iodide in solution, a series of arylated propargylamines and allylamines were synthesised and isolated as their acetamides. From the polymer-bound propargylamine, various allene amides were obtained after N-acylation followed by the Crabbé reaction. It was also briefly explored if the arylation of propargylamine on solid-phase could be possible without expensive palladium via the Castro-Stephens reaction, using a polymer-bound copper acetylide and the aryl iodide in solution. However, attempts to perform the first Castro Stephens reaction on solid-phase failed. Free amines are problematic in the Sonogashira and Heck reactions, due to coordination with the palladium catalyst and nucleophilicity toward the allene in the Crabbé reaction. These incompatibilities were solved by using the resin linkers simultaneously as protecting groups for the amines: as carbamates in the Sonogashira and Heck reaction, and as N-acyltriazenes in the Crabbé reaction. For the Heck reaction, finding the right reaction conditions turned out to be particularly difficult, the additional challenges being the narrow temperature window and the need to avoid polyarylation. Nevertheless, a regioselective γ-arylation could be performed giving similar yields as in the Sonogashira studies. In summary, alternative methods to perform important carbon carbon bond-forming reactions on solid support were developed.