Matemaattis-luonnontieteellinen tiedekunta


Recent Submissions

  • Arola, Teppo (Helsingin yliopisto, 2015)
    Increase of greenhouse gas concentrations in the atmosphere, the limits of conventional energy reservoirs and the instability risks related to energy transport have forced nations to promote the utilisation of renewable energy reservoirs. Groundwater can be seen as an option for renewable energy utilisation and not only a source of individual or municipal drinking water. Finland has multiple groundwater reservoirs that are easily exploitable, but groundwater energy is not commonly used for renewable energy production. The purpose of this thesis study was to explore the groundwater energy potential in Finland, a region with low temperature groundwater. Cases at three different scales were investigated to provide a reliable assessment of the groundwater energy potential in Finland. Firstly, the national groundwater energy potential was mapped for aquifers classified for water supply purposes that are under urban or industrial land use. Secondly, the urbanisation effect on the peak heating and peak cooling power of groundwater was investigated for three Finnish cities, and finally, the long-term groundwater energy potential was modelled for 20 detached houses, 3 apartment buildings and a shopping centre. The thesis connects scientific information on hydro- and thermogeology with the energy efficiency of buildings to produce accurate information concerning groundwater energy utilisation. Hydrological and thermogeological data were used together with accurate data on the energy demands of buildings. The heating and cooling power of groundwater was estimated based on the groundwater flux, temperature and heat capacity and the efficiency of the heat transfer system. The power producible from groundwater was compared with the heating and cooling demands of buildings to calculate the concrete groundwater energy potential. Approximately 20% to 40% of annually constructed residential buildings could be heated utilising groundwater from classified aquifers that already are under urban land use in Finland. These aquifers contain approximately 40 to 45 MW of heating power. In total, 55 to 60 MW of heat load could be utilised with heat pumps. Urbanisation increases the heating energy potential of groundwater. This is due anthropogenic heat flux to the subsurface, which increases the groundwater temperatures in urbanised areas. The average groundwater temperature was 3 to 4 °C higher in city centres than in rural areas. Approximately 50% to 60% more peak heating power could be utilised from urbanised compared with rural areas. Groundwater maintained its long term heating and cooling potential during 50 years of modelled operation in an area where the natural groundwater temperature is 4.9 °C. Long-term energy utilisation created a cold groundwater plume downstream, in which the temperature decreased by 1 to 2.5 °C within a distance of 300 m from the site. Our results demonstrate that groundwater can be effectively utilised down to a temperature of 4 °C. Groundwater can form a significant local renewable energy resource in Finland. It is important to recognise and utilise all renewable energy reservoirs to achieve the internationally binding climatological targets of the country. Groundwater energy utilisation should be noted as one easily exploitable option to increase the use of renewable energy resources in a region where the natural groundwater temperature is low. The methods presented in this thesis can be applied when mapping and designing groundwater energy systems in nationwide- to property-scale projects. Accurate information on hydro- and thermogeology together with the energy demands of buildings is essential for successful system operation.
  • Fagerholm, Fabian (Helsingin yliopisto, 2015)
    Human factors have been identified as having the largest impact on performance and quality in software development. While production methods and tools, such as development processes, methodologies, integrated development environments, and version control systems, play an important role in modern software development, the largest sources of variance and opportunities for improvement can be found in individual and group factors. The success of software development projects is highly dependent on cognitive, conative, affective, and social factors among individuals and groups. When success is considered to include not only fulfilment of schedules and profitability, but also employee well-being and public impact, particular attention must be paid to software developers and their experience of the software development activity. This thesis uses a mixed-methods research design, with case studies conducted in contemporary software development environments, to develop a theory of software developer experience. The theory explains what software developers experience as part of the development activity, how an experience arises, how the experience leads to changes in software artefacts and the development environment through behaviour, and how the social nature of software development mediates both the experience and outcomes. The theory can be used both to improve software development work environments and to design further scientific studies on developer experience. In addition, the case studies provide novel insights into how software developers experience software development in contemporary environments. In Lean-Agile software development, developers are found to be engaged in a continual cycle of Performance Alignment Work, where they become aware of, interpret, and adapt to performance concerns on all levels of an organisation. High-performing teams can successfully carry out this cycle and also influence performance expectations in other parts of the organisation and beyond. The case studies show that values arise as a particular concern for developers. The combination of Lean and Agile software development allows for a great deal of flexibility and self-organisation among developers. As a result, developers themselves must interpret the value system inherent in these methodologies in order to inform everyday decision-making. Discrepancies in the understanding of the value system may lead to different interpretations of what actions are desirable in a particular situation. Improved understanding of values may improve decision-making and understanding of Lean-Agile software development methodologies among software developers. Organisations may wish to clarify the value system for their particular organisational culture and promote values-based leadership for their software development projects. The distributed nature and use of virtual teams in Open Source environments present particular challenges when new members are to join a project. This thesis examines mentoring as a particular form of onboarding support for new developers. Mentoring is found to be a promising approach which helps developers adopt the practices and tacit conventions of an Open Source project community, and to become contributing members more rapidly. Mentoring could also have utility in similar settings that use virtual teams.
  • Punkka, Ari-Juhani (Helsingin yliopisto, 2015)
    Mesoscale convective systems (MCSs) are common in Finland and nearby regions. These conglomerates of cumulonimbus clouds have a diameter in excess of 100 km and lifetime of at least four hours. About 200 MCSs are detected every year out of which roughly 80 are classified as intense MCSs (maximum radar reflectivity exceeding 50 dBZ for two consecutive hours). MCSs occur most frequently during the afternoon hours in July and August, whereas in the wintertime, they are very few in number. Also the most extreme forms of MCSs such as derechos occur in Finland but only infrequently. The average duration of the MCSs is 10.8 hours in Finland and the most common direction of movement is toward the northeast. In the light of earlier MCS research a local peculiarity is the limited population of MCSs which has a motion component towards the west. The synoptic-scale weather pattern affects the MCS motion direction. An area of low pressure and upper-level trough are located west of Finland during many MCS situations which leads to the onset of southern air flow and the increase of low-tropospheric temperature and humidity. Based on the case studies in this thesis, the area of low pressure occasionally travels to the southwest of Finland enabling southeasterly air flow and further, the MCS motion component towards the west. During the thunderstorms days with sub-MCS deep moist convection, a northwesterly air flow and a ridge of high pressure west of Finland are frequently observed. As opposed to many earlier MCS studies, mid-level lapse rate does not distinguish between the MCS and sub-MCS environments in Finland. Instead, convective available potential energy (CAPE), low-tropospheric water vapour mixing ratio and deep-layer mean wind are able to distinguish between the aforementioned environments. Moreover, mean wind parameters are among the best discriminators between the days with significant and insignificant wind damage. Unlike in many earlier investigations, no evidence is found that cases with dry low- or mid-troposphere air would be more prone to the occurrence of significant convective winds than cases with moister environments. These results and the case studies propose that in the presence of low instability dry air dampens deep moist convection and convective downdrafts. However, in the presence of high instability the effect of dry air may be reverse, as the derecho case of 5 July 2002 (Unto) suggests.
  • Tomperi, Päivi (Helsingin yliopisto, 2015)
    Both nationally and internationally, teachers professional development is a current research topic. According to international teaching and learning survey TALIS, Finnish teachers interest to participate in long-lasting in-service teacher training programs, focusing on professional development, is decreasing. In order to implement inquiry-based practical work into classroom practice, new in-service training models are needed. This thesis examines the design and development process of a professional training course, which implemented the SOLO-taxonomy. The training course was meant for chemistry teachers working at the upper-secondary school and it focused on inquiry-based chemistry instruction. The research was done using design research. The main research questions were formed according to the three central areas of design research (Edelson, 2002): 1) Problem analysis: What kind of challenges does inquiry-based practical chemistry bring to chemistry teachers at the upper secondary school, 2) Design process: What kind of possibilities and challenges does the SOLO-taxonomy offer for the support of inquiry-based practical chemistry instruction and 3) Design solution: What are the characteristics of teachers professional development that promotes inquiry-based practice in chemistry at the upper secondary school? The eight-phase design research employed qualitative research methods, including observations, surveys and interviews. The data was analyzed using content analysis. From this data, two main research results were obtained. First, information was obtained on the implementation of inquiry-based chemistry into practice, and about teachers professional development using the SOLO-taxonomy. Second, information on the characteristics of research-based training model promoting inquiry-based practical chemistry instruction was obtained. The findings show that inquiry is challenging for teachers due to its constructivist view on learning, teachers inexperience to act in modern learning environments and not practicing implementing inquiry in the classroom during training. The findings also show that using the SOLO-taxonomy supported professional development in many ways. For example, it worked as a tool in designing and modifying written instructions, it motivated teachers to develop their practices, it increased teachers ownership to the produced written instructions, it supported teachers understanding of inquiry and it acted as a model to support higher-order thinking skills. The created research-based training model, meant to promote inquiry in practical chemistry instruction, was based on a theoretical and empirical problem analysis. The main features incorporated into the training model are (i) personalized learning which considers the teachers current knowledge (ii) expanding teacher s role from merely a dispenser of knowledge to the roles of a researcher and a learner, (iii) using a theoretical framework to support research-based instruction, higher-order thinking skills and interaction-based sharing of ideas, (iv) creating meaningful inquiry-based material, done using the SOLO-taxonomy, (v) peer-support (vi) reflection and incorporation of action research, (vii) practicing implementing inquiry-based practical work, which is of collaborative and cognitive nature increasing understanding of the nature of science. The research results show that teachers need training models of various durations. If the teacher s view of learning is congruous with the inquiry-based approach, they can begin to practice the implementation of inquiry already during a short training. However, if the teachers view on learning does not support constructive learning methods, the accommodation process requires more time. The research results of this doctoral dissertation can be applied (i) in the implementation of new national core curriculum, (ii) in planning and designing new learning material for inquiry-based practical chemistry (iii) in training that supports teachers life-long learning, and (iv) in international exportation of education. Keywords: Design research, professional development, SOLO-taxonomy, research-based training, inquiry-based practical chemistry
  • Franchin, Alessandro (Helsingin yliopisto, 2015)
    This thesis focuses on the experimental characterization of secondary atmospheric nanoparticles and ions during their formation. This work was developed in two distinct and complementary levels: a scientific level, aimed to advance the understanding of particle formation and a more technical level, dedicated to instrument development and characterization. Understanding and characterizing aerosol formation, is important, as formation of aerosol particles from precursor gases is one of the main sources of atmospheric aerosols. Elucidating how aerosol formation proceeds in detail is critical to better quantify aerosol contribution to the Earth's radiation budget. Experimentally characterizing the first steps of aerosol formation is the key to understanding this phenomenon. Developing and characterizing suitable instrumentation to measure clusters and ions in the sub 3 nm range, where aerosol formation starts, is necessary to clarify the processes that lead to aerosol formation. This thesis presents the results of a series of experimental studies of sub 3 nm aerosol particles and ions. It also shows the results of the technical characterization and instrument development that were made in the process. Specifically, we describe three scientific results achieved from chamber experiments. Firstly the relative contributions of sulfuric acid, ammonia and ions in nucleation processes was quantified experimentally, supporting that sulfuric acid alone cannot explain atmospheric observation of nucleation rates. Secondly, the chemical composition of cluster ions was directly measured for a ternary system, where sulfuric acid, ammonia and water were the condensable vapors. In these measurements we observed a decreasing acidity of the clusters with increasing concentration of gas phase ammonia, with the ratio of sulfuric acid/ammonia staying closer to that of ammonium bisulfate than to that of ammonium sulfate. Finally, in a series of chamber experiments the ion ion recombination coefficient was quantified at different conditions. The ion ion recombination coefficient is a basic physical quantity for modeling ion induced and ion mediated nucleation. We observed a steep increase in the ion ion recombination coefficient with decreasing temperatures and with decreasing relative humidity. This thesis also reviews technical results of: 1) laboratory verification, characterization and testing of different aerosol and ion instruments measuring in the sub 3 nm range; 2) the development of new inlets for such instruments to improve the detection of sub-3 nm particles and ions.
  • 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.
  • Peltola, Jari (Helsingin yliopisto, 2015)
    This thesis is based on four experimental spectroscopic studies where novel highly sensitive laser absorption spectroscopy spectrometers are developed and used for trace gas detection and precision spectroscopy. Most of the studies are carried out in the mid-infrared region between 3 and 4 µm, where a homebuilt continuous-wave singly resonating optical parametric oscillator is used as a light source. In addition, one study has been performed in the visible region using a commercial green laser at 532 nm. Two of the developed spectroscopic applications are based on cavity ring-down spectroscopy. In this thesis, the first off-axis re-entrant cavity ring-down spectrometer in the mid-infrared is demonstrated and utilized for highly sensitive detection of formaldehyde. The second study presents an optical frequency comb referenced mid-infrared continuous-wave singly resonating optical parametric oscillator, which is applied to high-precision cavity ring-down spectroscopy of nitrous oxide and methane. Furthermore, this study presents a new method for referencing a mid-infrared optical parametric oscillator to a near-infrared optical frequency comb. This new method allows large mode-hop-free frequency tuning ranges in the mid-infrared region. The other two experiments are based on cantilever-enhanced photoacoustic spectroscopy, presenting the first reported studies of cantilever-enhanced-based trace gas detection in the mid-infrared and visible region. These studies show the great potential of cantilever-enhanced photoacoustic detection for substantial enhancement of the sensitivity of trace gas detection. For instance, the best nitrogen dioxide detection limit ever reported using photoacoustic spectroscopy is presented in this thesis.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.