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  • Grönholm, Tiia (Helsingin yliopisto, 2012)
    Dry and wet deposition are removal mechanisms of atmospheric aerosol particles. Historically, there are very scarce scientic publications reporting experimentally determined dry deposition values for the ultra-fine size range. The physics of deposition is studied both using micrometeorological field measurements conducted at SMEAR II site in Hyytiälä, Southern Finland and by modeling approaches. Dry deposition velocity depends mainly on particle size and magnitude of the atmospheric surface layer turbulence. We present experimentally determined dry deposition velocity (vd) as a function of particle size for the ultra- fine aerosol size range (10 - 150 nm) using relaxed eddy accumulation and eddy-covariance (EC) methods accompanied by particle number size distribution measurements. The highest vd was found for 10 nm particles and in all size classes vd increased with increasing friction velocity. By combining two-layer (above and sub-canopy) EC measurements and a new multi-layer canopy deposition model, we addressed how dry deposition is distributed within the forest canopy and between the canopy and the underlying ground. According to the measurements, about 20 - 30 % of particles penetrated the canopy and deposited on the forest floor. The model results showed that turbophoresis, when accounted for at the leaf scale in vertically resolved models, could increase vd for 0.1 - 2 nm particles and explain why the observations over forests generally do not support the pronounced minimum of deposition velocity for particles of that size. The developed multi-layer model was further used to study the effect of canopy structure (leaf-area shape and density) on vd. Scavenging coefficients for rain and snow deposition were calculated based on measurements of particle size distribution and precipitation. Parameterizations for both rain and snow wet deposition were derived for example to be applied in air quality and global models. Also a model including both in-cloud and below cloud wet deposition was developed and compared to the field measurements. Both snow and rain scavenging efficiency increased with increasing precipitation intensity. We also found, that the effectiveness of snow scavenging depends on the crystal or snow flake structure and the air relative humidity. Wet deposition was found to be an order of magnitude more effective "air cleaner" compared to dry deposition.
  • Pohjoispää, Monika (Helsingin yliopisto, 2014)
    Lignans are naturally occurring compounds, polyphenolic secondary plant and mammalian metabolites. Due to their ubiquitous presence and biological activity, lignans have attracted the interest of scientists from different areas, like nutrition scientists, pharmaceutical researchers and synthetic chemists. The research is very active, and the number of lignan related publications has proliferated. Lignans vary widely in the structure, and the present work focuses mainly on the (hydroxy)lignano-­9,9’­‐lactones, their rearranged products, and 9,9’-­epoxylignanes. The literature review introduces the stereochemistry and assignment of the absolute configuration of these lignans. In addition, stable isotope labelling of lignans is reviewed. The experimental part is focused on deuteration of lignans and rearrangement and stereochemistry studies. The deuteration reaction utilising acidic H/D exchange within the lignan skeleton was investigated. The relative reactivity of various aromatic sites, the stability of deuterium labels and the isotopic purity of the labelled compounds were examined. Experimental observations and results were compared to computational studies. Several stable, isotopically pure polydeuterated lignano-­9,9’-lactones and 9,9’-­epoxylignanes were synthesised. Alongside the deuteration experiments unexpected reactivity in eletrophilic aromatic deuteration of methylenedioxy substituted compounds was observed and further studied. In addition to deuteration, the stereochemistry of certain rearranged lignanolactones was a central subject of this study. Our findings allowed to clarify some mechanistical aspects of the rearrangement reactions of 7’-­hydroxylignano-­9,9’-­lactones and revise certain disputable structural data in the literature. Furthermore, the X-­ray structures of 7’-hydroxylignano-­9,9’-­lactones and rearranged 9’-hydroxylignano-­9,7’-­lactones were obtained for the first time.
  • Salminen, Susanna (Helsingin yliopisto, 2009)
    In this work, separation methods have been developed for the analysis of anthropogenic transuranium elements plutonium, americium, curium and neptunium from environmental samples contaminated by global nuclear weapons testing and the Chernobyl accident. The analytical methods utilized in this study are based on extraction chromatography. Highly varying atmospheric plutonium isotope concentrations and activity ratios were found at both Kurchatov (Kazakhstan), near the former Semipalatinsk test site, and Sodankylä (Finland). The origin of plutonium is almost impossible to identify at Kurchatov, since hundreds of nuclear tests were performed at the Semipalatinsk test site. In Sodankylä, plutonium in the surface air originated from nuclear weapons testing, conducted mostly by USSR and USA before the sampling year 1963. The variation in americium, curium and neptunium concentrations was great as well in peat samples collected in southern and central Finland in 1986 immediately after the Chernobyl accident. The main source of transuranium contamination in peats was from global nuclear test fallout, although there are wide regional differences in the fraction of Chernobyl-originated activity (of the total activity) for americium, curium and neptunium.
  • Jernström, Jussi (Helsingin yliopisto, 2006)
    Radioactive particles from three locations were investigated for elemental composition, oxidation states of matrix elements, and origin. Instrumental techniques applied to the task were scanning electron microscopy, X-ray and gamma-ray spectrometry, secondary ion mass spectrometry, and synchrotron radiation based microanalytical techniques comprising X-ray fluorescence spectrometry, X-ray fluorescence tomography, and X-ray absorption near-edge structure spectroscopy. Uranium-containing low activity particles collected from Irish Sea sediments were characterized in terms of composition and distribution of matrix elements and the oxidation states of uranium. Indications of the origin were obtained from the intensity ratios and the presence of thorium, uranium, and plutonium. Uranium in the particles was found to exist mostly as U(IV). Studies on plutonium particles from Runit Island (Marshall Islands) soil indicated that the samples were weapon fuel fragments originating from two separate detonations: a safety test and a low-yield test. The plutonium in the particles was found to be of similar age. The distribution and oxidation states of uranium and plutonium in the matrix of weapon fuel particles from Thule (Greenland) sediments were investigated. The variations in intensity ratios observed with different techniques indicated more than one origin. Uranium in particle matrixes was mostly U(IV), but plutonium existed in some particles mainly as Pu(IV), and in others mainly as oxidized Pu(VI). The results demonstrated that the various techniques were effectively applied in the characterization of environmental radioactive particles. An on-line method was developed for separating americium from environmental samples. The procedure utilizes extraction chromatography to separate americium from light lanthanides, and cation exchange to concentrate americium before the final separation in an ion chromatography column. The separated radiochemically pure americium fraction is measured by alpha spectrometry. The method was tested with certified sediment and soil samples and found to be applicable for the analysis of environmental samples containing a wide range of Am-241 activity. Proceeding from the on-line method developed for americium, a method was also developed for separating plutonium and americium. Plutonium is reduced to Pu(III), and separated together with Am(III) throughout the procedure. Pu(III) and Am(III) are eluted from the ion chromatography column as anionic dipicolinate and oxalate complexes, respectively, and measured by alpha spectrometry.
  • Alexey, Adamov (Helsingin yliopisto, 2012)
    This study is focused on the development and evaluation of ion mobility instrumentation with various atmospheric pressure ionization techniques and includes the following work. First, a high-resolution drift tube ion mobility spectrometer (IMS), coupled with a commercial triple quadrupole mass spectrometer (MS), was developed. This drift tube IMS is compatible with the front-end of commercial Sciex mass spectrometers (e.g., Sciex API-300, 365, and 3000) and also allows easy (only minor modifications are needed) installation between the original atmospheric pressure ion source and the triple quadrupole mass spectrometer. Performance haracteristics (e.g.,resolving power, detection limit, transmission efficiency of ions) of this IMS-MS instrument were evaluated. Development of the IMS-MS instrument also led to a study where a proposal was made that tetraalkylammonium ions can be used as chemical standards for ESI-IMS. Second, the same drift tube design was also used to build a standalone ion mobility spectrometer equipped with a Faraday plate detector. For this highresolution (resolving power about 100 shown) IMS device, a multi-ion source platform was built, which allows the use of a range of atmospheric pressure ionization methods, such as: corona discharge chemical ionization (CD-APCI), atmospheric pressure photoionization (APPI), and radioactive atmospheric pressure chemical ionization (R-APCI). The multi-ion source platform provides easy switching between ionization methods and both positive and negative ionization modes can be used. Third, a simple desorpion/ionization on silicon (DIOS) ion source set-up for use with the developed IMS and IMS-MS instruments was built and its operation demonstrated. Fourth, a prototype of a commercial aspiration-type ion mobility spectrometer was mounted in front of a commercial triple quadrupole mass spectrometer. The set-up, which is simple, easy to install, and requires no major modifications to the MS, provides the possibility of gathering fundamental information about aspiration mobility spectrometry.
  • Tarvainen, Virpi (Helsingfors universitet, 2008)
    The volatile organic compounds (VOCs) emitted by vegetation, especially forests, can affect local and regional atmospheric photochemistry through their reactions with atmospheric oxidants. Their reaction products may also participate in the formation and growth of new particles which affect the radiation balance of the atmosphere, and thus climate, by scattering and absorbing shortwave and longwave radiation and by modifying the radiative properties, amount and lifetime of clouds. Globally, anthropogenic VOC emissions are far surpassed by the biogenic ones, making biogenic emission inventories an integral element in the development of efficient air quality and climate strategies. This thesis is focused on the VOC emissions from the boreal forest, the largest terrestrial biome with characteristic vegetation patterns and strong seasonality. The isoprene, monoterpene and sesquiterpene emissions of the most prevalent boreal tree species in Finland, Scots pine, have been measured and their seasonal variation and dependence on temperature and light have been studied. The measured emission data and other available observations of the emissions of the principal boreal trees have been used in a biogenic emission model developed for the forests in Finland. The model utilizes satellite landcover information, Finnish forest classification and hourly meteorological data to calculate isoprene, monoterpene, sesquiterpene and other VOC emissions over the growing season. The main compounds emitted by the boreal forest throughout the growing season in Finland are alpha- and beta-pinene and delta-carene, with a strong contribution of sabinene by the deciduous trees in summer and autumn. The emissions follow the course of the temperature and are highest in the south boreal zone with a steady decline towards the north. The isoprene emissions from the boreal forest are fairly low - the main isoprene emitters are the low emitting Norway spruce and the high emitting willow and aspen, whose foliage, however, only represents a very small percentage of the boreal leaf biomass. This work also includes the first estimate of sesquiterpene emissions from the boreal forest. The sesquiterpene emissions initiate after midsummer and are of the same order of magnitude as the isoprene emissions. At the annual level, the total biogenic emissions from the forests in Finland are approximately twice the anthropogenic VOC emissions.
  • Vastamäki, Pertti (Helsingin yliopisto, 2014)
    This research work was focused on the development of instrumentation, operations, and approximate theory of a new continuous two-dimensional thermal field-flow fractionation (2D-ThFFF) technique for the separation and collection of macromolecules and particles. The separation occur in a thin disk-shaped channel, where a carrier liquid flows radially from the center towards the perimeter of the channel, and a steady stream of the sample solution is introduced continuously at a second inlet close to the center of the channel. Under influence of the thermal field, the sample components are separated in radial direction according to the analytical ThFFF principle. Simultaneously, the lower channel wall is rotating with respect to the stationary upper wall, while a shear-driven flow profile deflects the separated sample components into continuous trajectories that strike off at different angles over the 2D surface. Finally, the sample components are collected at the outer rim of the channel, and the sample concentrations in each fraction are determined with the analytical ThFFF. The samples were polystyrene polymer standards and the carrier solvents cyclohexane and cyclohexane-ethylbenzene mixture in continuous 2D-ThFFF and tetrahydrofuran in analytical ThFFF. The thermal field had a positive effect on the sample deflection, although broadening of the sample zone was observed. Decreasing the channel thickness and the radial and angular flow rates of the carrier caused significant narrowing of the zone broadening. Systematic variation of the experimental parameters allowed determination of the conditions required for the continuous fractionation of polystyrene polymers according to their molar mass. As an example, almost baseline separation was achieved with two polystyrene samples of different molar masses. Meanwhile, an approximate theoretical model was developed for prediction of the trajectory of the sample component zone and its angular displacement under various operating conditions. The trends in the deflection angles without and with a thermal gradient were qualitatively in agreement with predictions of the model, but significant quantitative differences were found between the theoretical predictions and experimental results. The reasons for discrepancies between theory and experiment could be the following: relaxation of the sample already at the sample inlet, effect of solvent partition when binary solvent is used as the carrier, dispersion of the sample, limitations of the instrument, and geometrical imperfections. Despite its incompleteness, the theoretical model will provide guidelines for future interpretation and optimization of separations by continuous 2D-ThFFF method.
  • Lipponen, Katriina (Helsingin yliopisto, 2014)
    This doctoral thesis focuses on the development of miniaturized biosensing systems for the study of biomolecular interactions. Acoustic biosensor quartz crystal microbalance (QCM), partial filling affinity capillary electrophoresis (PF-ACE), and open-tubular capillary electrochromatography (OT-CEC) were developed to allow study of interactions between glycosaminoglycans and lipoproteins, which are responsible for the accumulation of low density lipoprotein (LDL) on the arterial wall. The first step was to develop suitable coating methods for the immobilization of selected glycosaminoglycans on chip and capillary surfaces and to develop a neutral capillary surface for PF-ACE studies. Evaluation of different coating procedures demonstrated the significance of the procedure for the successful outcome of biological interaction studies. With suitable platforms available for the instrumental techniques in question, studies of interactions between glycosaminoglycans and lipoprotein particles were carried out to evaluate the strength of the binding processes. Affinity constants, retention factors, and reduced mobilities were measured. Since the commonly used approaches typically allow only the strongest binding site of the system to be determined, the scope of the investigation was broadened by introducing adsorption energy distribution (AED) calculations in the processing of QCM and PF-ACE data. Finally, molecular dynamics (MD) simulations were used as a supportive tool to visualize and study interactions at the atomic level. In addition, microscale thermophoresis, a relatively new technique, was used to complement and support some of the experimental studies. The results obtained by QCM methods, PF-ACE, OT-CEC, and MD simulations were in good agreement. Even minor changes in the binding process could be visualized by exploiting AED calculations in the data processing step. The main advantages of all three experimental methods were low sample consumption, relatively fast analysis times, and the possibility to evaluate the heterogeneity of the interactions. The findings of the work demonstrate the great potential of the developed biosensing systems for biomolecular interaction and biomimicking studies. Of particular interest is the availability of information on heterogeneous reactions when AED calculations are applied in the interpretation of QCM and PF-ACE results.
  • Koivula, Teija (Helsingin yliopisto, 2011)
    Positron emission tomography (PET) is a molecular imaging technique that utilises radiopharmaceuticals (radiotracers) labelled with a positron-emitting radionuclide, such as fluorine-18 (18F). Development of a new radiotracer requires an appropriate radiosynthesis method: the most common of which with 18F is nucleophilic substitution with [18F]fluoride ion. The success of the labelling reaction is dependent on various factors such as the reactivity of [18F]fluoride, the structure of the target compound in addition to the chosen solvent. The overall radiosynthesis procedure must be optimised in terms of radiochemical yield and quality of the final product. Therefore, both quantitative and qualitative radioanalytical methods are essential in developing radiosynthesis methods. Furthermore, biological properties of the tracer candidate need to be evaluated by various pre-clinical studies in animal models. In this work, the feasibility of various nucleophilic 18F-fluorination strategies were studied and a labelling method for a novel radiotracer, N-3-[18F]fluoropropyl-2beta-carbomethoxy-3beta-4-fluorophenyl)nortropane ([18F]beta-CFT-FP), was optimised. The effect of solvent was studied by labelling a series of model compounds, 4-(R1-methyl)benzyl R2-benzoates. 18F-Fluorination reactions were carried out both in polar aprotic and protic solvents (tertiary alcohols). Assessment of the 18F-fluorinated products was studied by mass spectrometry (MS) in addition to conventional radiochromatographic methods, using radiosynthesis of 4-[18F]fluoro-N-[2-[1-(2-methoxyphenyl)-1-piperazinyl]ethyl-N-2-pyridinyl-benzamide (p-[18F]MPPF) as a model reaction. Labelling of [18F]beta-CFT-FP was studied using two 18F-fluoroalkylation reagents, [18F]fluoropropyl bromide and [18F]fluoropropyl tosylate, as well as by direct 18F-fluorination of sulfonate ester precursor. Subsequently, the suitability of [18F]beta-CFT-FP for imaging dopamine transporter (DAT) was evaluated by determining its biodistribution in rats. The results showed that protic solvents can be useful co-solvents in aliphatic 18F-fluorinations, especially in the labelling of sulfonate esters. Aromatic 18F-fluorination was not promoted in tert-alcohols. Sensitivity of the ion trap MS was sufficient for the qualitative analysis of the 18F-labelled products; p-[18F]MPPF was identified from the isolated product fraction with a mass-to-charge (m/z) ratio of 435 (i.e. protonated molecule [M+H]+). [18F]beta-CFT-FP was produced most efficiently via [18F]fluoropropyl tosylate, leading to sufficient radiochemical yield and specific radioactivity for PET studies. The ex vivo studies in rats showed fast kinetics as well as the specific uptake of [18F]beta-CFT-FP to the DAT rich brain regions. Thus, it was concluded that [18F]beta-CFT-FP has potential as a radiotracer for imaging DAT by PET.
  • Kivilompolo, Maarit (Helsingin yliopisto, 2009)
    In this study, novel methodologies for the determination of antioxidative compounds in herbs and beverages were developed. Antioxidants are compounds that can reduce, delay or inhibit oxidative events. They are a part of the human defense system and are obtained through the diet. Antioxidants are naturally present in several types of foods, e.g. in fruits, beverages, vegetables and herbs. Antioxidants can also be added to foods during manufacturing to suppress lipid oxidation and formation of free radicals under conditions of cooking or storage and to reduce the concentration of free radicals in vivo after food ingestion. There is growing interest in natural antioxidants, and effective compounds have already been identified from antioxidant classes such as carotenoids, essential oils, flavonoids and phenolic acids. The wide variety of sample matrices and analytes presents quite a challenge for the development of analytical techniques. Growing demands have been placed on sample pretreatment. In this study, three novel extraction techniques, namely supercritical fluid extraction (SFE), pressurised hot water extraction (PHWE) and dynamic sonication-assisted extraction (DSAE) were studied. SFE was used for the extraction of lycopene from tomato skins and PHWE was used in the extraction of phenolic compounds from sage. DSAE was applied to the extraction of phenolic acids from Lamiaceae herbs. In the development of extraction methodologies, the main parameters of the extraction were studied and the recoveries were compared to those achieved by conventional extraction techniques. In addition, the stability of lycopene was also followed under different storage conditions. For the separation of the antioxidative compounds in the extracts, liquid chromatographic methods (LC) were utilised. Two novel LC techniques, namely ultra performance liquid chromatography (UPLC) and comprehensive two-dimensional liquid chromatography (LCxLC) were studied and compared with conventional high performance liquid chromatography (HPLC) for the separation of antioxidants in beverages and Lamiaceae herbs. In LCxLC, the selection of LC mode, column dimensions and flow rates were studied and optimised to obtain efficient separation of the target compounds. In addition, the separation powers of HPLC, UPLC, HPLCxHPLC and HPLCxUPLC were compared. To exploit the benefits of an integrated system, in which sample preparation and final separation are performed in a closed unit, dynamic sonication-assisted extraction was coupled on-line to a liquid chromatograph via a solid-phase trap. The increased sensitivity was utilised in the extraction of phenolic acids from Lamiaceae herbs. The results were compared to those of achieved by the LCxLC system.
  • Honkonen, Ilja (Helsingin yliopisto, 2013)
    Currently the majority of space-based assets are located inside the Earth's magnetosphere where they must endure the effects of the near-Earth space environment, i.e. space weather, which is driven by the supersonic flow of plasma from the Sun. Space weather refers to the day-to-day changes in the temperature, magnetic field and other parameters of the near-Earth space, similarly to ordinary weather which refers to changes in the atmosphere above ground level. Space weather can also cause adverse effects on the ground, for example, by inducing large direct currents in power transmission systems. The performance of computers has been growing exponentially for many decades and as a result the importance of numerical modeling in science has also increased rapidly. Numerical modeling is especially important in space plasma physics because there are no in-situ observations of space plasmas outside of the heliosphere and it is not feasible to study all aspects of space plasmas in a terrestrial laboratory. With the increasing number of computational cores in supercomputers, the parallel performance of numerical models on distributed memory hardware is also becoming crucial. This thesis consists of an introduction, four peer reviewed articles and describes the process of developing numerical space environment/weather models and the use of such models to study the near-Earth space. A complete model development chain is presented starting from initial planning and design to distributed memory parallelization and optimization, and finally testing, verification and validation of numerical models. A grid library that provides good parallel scalability on distributed memory hardware and several novel features, the distributed cartesian cell-refinable grid (DCCRG), is designed and developed. DCCRG is presently used in two numerical space weather models being developed at the Finnish Meteorological Institute. The first global magnetospheric test particle simulation based on the Vlasov description of plasma is carried out using the Vlasiator model. The test shows that the Vlasov equation for plasma in six-dimensionsional phase space is solved correctly by Vlasiator, that results are obtained beyond those of the magnetohydrodynamic (MHD) description of plasma and that global magnetospheric simulations using a hybrid-Vlasov model are feasible on current hardware. For the first time four global magnetospheric models using the MHD description of plasma (BATS-R-US, GUMICS, OpenGGCM, LFM) are run with identical solar wind input and the results compared to observations in the ionosphere and outer magnetosphere. Based on the results of the global magnetospheric MHD model GUMICS a hypothesis is formulated for a new mechanism of plasmoid formation in the Earth's magnetotail.
  • Hellsten, Alex (Helsingin yliopisto, 2003)
  • Mäntylä, Terhi (Helsingin yliopisto, 2011)
    Physics teachers are in a key position to form the attitudes and conceptions of future generations toward science and technology, as well as to educate future generations of scientists. Therefore, good teacher education is one of the key areas of physics departments education program. This dissertation is a contribution to the research-based development of high quality physics teacher education, designed to meet three central challenges of good teaching. The first challenge relates to the organization of physics content knowledge. The second challenge, connected to the first one, is to understand the role of experiments and models in (re)constructing the content knowledge of physics for purposes of teaching. The third challenge is to provide for pre-service physics teachers opportunities and resources for reflecting on or assessing their knowledge and experience about physics and physics education. This dissertation demonstrates how these challenges can be met when the content knowledge of physics, the relevant epistemological aspects of physics and the pedagogical knowledge of teaching and learning physics are combined. The theoretical part of this dissertation is concerned with designing two didactical reconstructions for purposes of physics teacher education: the didactical reconstruction of processes (DRoP) and the didactical reconstruction of structures (DRoS). This part starts with taking into account the required professional competencies of physics teachers, the pedagogical aspects of teaching and learning, and the benefits of the graphical ways of representing knowledge. Then it continues with the conceptual and philosophical analysis of physics, especially with the analysis of experiments and models role in constructing knowledge. This analysis is condensed in the form of the epistemological reconstruction of knowledge justification. Finally, these two parts are combined in the designing and production of the DRoP and DRoS. The DRoP captures the knowledge formation of physical concepts and laws in concise and simplified form while still retaining authenticity from the processes of how concepts have been formed. The DRoS is used for representing the structural knowledge of physics, the connections between physical concepts, quantities and laws, to varying extents. Both DRoP and DRoS are represented in graphical form by means of flow charts consisting of nodes and directed links connecting the nodes. The empirical part discusses two case studies that show how the three challenges are met through the use of DRoP and DRoS and how the outcomes of teaching solutions based on them are evaluated. The research approach is qualitative; it aims at the in-depth evaluation and understanding about the usefulness of the didactical reconstructions. The data, which were collected from the advanced course for prospective physics teachers during 20012006, consisted of DRoP and DRoS flow charts made by students and student interviews. The first case study discusses how student teachers used DRoP flow charts to understand the process of forming knowledge about the law of electromagnetic induction. The second case study discusses how student teachers learned to understand the development of physical quantities as related to the temperature concept by using DRoS flow charts. In both studies, the attention is focused on the use of DRoP and DRoS to organize knowledge and on the role of experiments and models in this organization process. The results show that students understanding about physics knowledge production improved and their knowledge became more organized and coherent. It is shown that the flow charts and the didactical reconstructions behind them had an important role in gaining these positive learning results. On the basis of the results reported here, the designed learning tools have been adopted as a standard part of the teaching solutions used in the physics teacher education courses in the Department of Physics, University of Helsinki.
  • Keyriläinen, Jani (Helsingin yliopisto, 2004)