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  • Mäntyniemi, Päivi (Helsingin yliopisto, 2008)
    This work focuses on the role of macroseismology in the assessment of seismicity and probabilistic seismic hazard in Northern Europe. The main type of data under consideration is a set of macroseismic observations available for a given earthquake. The macroseismic questionnaires used to collect earthquake observations from local residents since the late 1800s constitute a special part of the seismological heritage in the region. Information of the earthquakes felt on the coasts of the Gulf of Bothnia between 31 March and 2 April 1883 and on 28 July 1888 was retrieved from the contemporary Finnish and Swedish newspapers, while the earthquake of 4 November 1898 GMT is an example of an early systematic macroseismic survey in the region. A data set of more than 1200 macroseismic questionnaires is available for the earthquake in Central Finland on 16 November 1931. Basic macroseismic investigations including preparation of new intensity data point (IDP) maps were conducted for these earthquakes. Previously disregarded usable observations were found in the press. The improved collection of IDPs of the 1888 earthquake shows that this event was a rare occurrence in the area. In contrast to earlier notions it was felt on both sides of the Gulf of Bothnia. The data on the earthquake of 4 November 1898 GMT were augmented with historical background information discovered in various archives and libraries. This earthquake was of some concern to the authorities, because extra fire inspections were conducted in three towns at least, i.e. Tornio, Haparanda and Piteå, located in the centre of the area of perceptibility. This event posed the indirect hazard of fire, although its magnitude around 4.6 was minor on the global scale. The distribution of slightly damaging intensities was larger than previously outlined. This may have resulted from the amplification of the ground shaking in the soft soil of the coast and river valleys where most of the population was found. The large data set of the 1931 earthquake provided an opportunity to apply statistical methods and assess methodologies that can be used when dealing with macroseismic intensity. It was evaluated using correspondence analysis. Different approaches such as gridding were tested to estimate the macroseismic field from the intensity values distributed irregularly in space. In general, the characteristics of intensity warrant careful consideration. A more pervasive perception of intensity as an ordinal quantity affected by uncertainties is advocated. A parametric earthquake catalogue comprising entries from both the macroseismic and instrumental era was used for probabilistic seismic hazard assessment. The parametric-historic methodology was applied to estimate seismic hazard at a given site in Finland and to prepare a seismic hazard map for Northern Europe. The interpretation of these results is an important issue, because the recurrence times of damaging earthquakes may well exceed thousands of years in an intraplate setting such as Northern Europe. This application may therefore be seen as an example of short-term hazard assessment.
  • Lukkari, Sari (Helsingin yliopisto, 2007)
    This study brings new insights into the magmatic evolution of natural F-enriched peraluminous granitic systems. The Artjärvi, Sääskjärvi and Kymi granite stocks within the 1.64 Ga Wiborg rapakivi granite batholith have been investigated by petrographic, geochemical, experimental and melt inclusion methods. These stocks represent late-stage leucocratic and weakly peraluminous intrusive phases typical of rapakivi granites worldwide. The Artjärvi and Sääskjärvi stocks are multiphase intrusions in which the most evolved phase is topaz granite. The Kymi stock contains topaz throughout and has a well-developed zoned structure, from the rim to the center: stockscheider pegmatite equigranular topaz granite porphyritic topaz granite. Geochemically the topaz granites are enriched in F, Li, Be, Ga, Rb, Sn and Nb and depleted in Mg, Fe, Ti, Ba, Sr, Zr and Eu. The anomalous geochemistry and mineralogy of the topaz granites are essentially magmatic in origin; postmagmatic reactions have only slightly modified the compositions. The Kymi equigranular topaz granite shows the most evolved character, and the topaz granites at Artjärvi and Sääskjärvi resemble the less evolved porphyritic topaz granite of the Kymi stock. Stockscheiders are found at the roof contacts of the Artjärvi and Kymi stocks. The stockscheider at Artjärvi is composed of biotite-rich schlieren and pegmatite layers parallel to the contact. The schlieren layering is considered to have formed by velocity-gradient sorting mechanism parallel to the flow, which led to the accumulation of mafic minerals along the upper contact of the topaz granite. Cooling and contraction of the topaz granite formed fractures parallel to the roof contact and residual pegmatite magmas were injected along the fractures and formed the pegmatite layers. The zoned structure of the Kymi stock is the result of intrusion of highly evolved residual melt from deeper parts of the magma chamber along the fractured contact between the porphyritic granite crystal mush and country rock. The equigranular topaz granite and marginal pegmatite (stockscheider) crystallized from this evolved melt. Phase relations of the Kymi equigranular topaz granite have been investigated utilizing crystallization experiments at 100 to 500 MPa as a function of water activity and F content. Fluorite and topaz can crystallize as liquidus phases in F-rich peraluminous systems, but the F content of the melt should exceed 2.5 - 3.0 wt % to facilitate crystallization of topaz. In peraluminous F-bearing melts containing more than 1 wt % F, topaz and muscovite are expected to be the first F-bearing phases to crystallize at high pressure, whereas fluorite and topaz should crystallize first at low pressure. Overall, the saturation of fluorite and topaz follows the reaction: CaAl2Si2O8 (plagioclase) + 2[AlF3]melt = CaF2 (fluorite) + 2Al2SiO4F2 (topaz). The obtained partition coefficient for F between biotite and glass D(F)Bt/glass is 1.89 to 0.80 (average 1.29) and can be used as an empirical fluormeter to determine the F content of coexisting melts. In order to study the magmatic evolution of the Kymi stock, crystallized melt inclusions in quartz and topaz grains in the porphyritic and the equigranular topaz granites and the marginal pegmatite were rehomogenized and analyzed. The homogenization conditions for the melt inclusions from the granites were 700 °C, 300 MPa, and 24 h, and for melt inclusions from the pegmatite, 700 °C, 100 MPa, and 24/96 h. The majority of the melt inclusions is chemically similar to the bulk rocks (excluding H2O content), but a few melt inclusions in the equigranular granite show clearly higher F and low K2O contents (on average 11.6 wt % F, 0.65 wt % K2O). The melt inclusion compositions indicate coexistence of two melt fractions, a prevailing peraluminous and a very volatile-rich, possibly peralkaline. Combined petrological, experimental and melt inclusion studies of the Kymi equigranular topaz granite indicate that plagioclase was the liquidus phase at nearly water-saturated (fluid-saturated) conditions and that the F content of the melt was at least 2 wt %. The early crystallization of biotite and the presence of muscovite in crystallization experiments at 200 MPa contrasts with the late-stage crystallization of biotite and the absence of muscovite in the equigranular granite, indicating that crystallization pressure may have been lower than 200 MPa for the granite.
  • Taubert, Stefan (Helsingin yliopisto, 2011)
    The magnetically induced currents in organic monoring and multiring molecules, in Möbius shaped molecules and in inorganic all-metal molecules have been investigated by means of the Gauge-including magnetically induced currents (GIMIC) method. With the GIMIC method, the ring-current strengths and the ring-current density distributions can be calculated. For open-shell molecules, also the spin current can be obtained. The ring-current pathways and ring-current strengths can be used to understand the magnetic resonance properties of the molecules, to indirectly identify the effect of non-bonded interactions on NMR chemical shifts, to design new molecules with tailored properties and to discuss molecular aromaticity. In the thesis, the magnetic criterion for aromaticity has been adopted. According to this, a molecule which has a net diatropic ring current might be aromatic. Similarly, a molecule which has a net paratropic current might be antiaromatic. If the net current is zero, the molecule is nonaromatic. The electronic structure of the investigated molecules has been resolved by quantum chemical methods. The magnetically induced currents have been calculated with the GIMIC method at the density-functional theory (DFT) level, as well as at the self-consistent field Hartree-Fock (SCF-HF), at the Møller-Plesset perturbation theory of the second order (MP2) and at the coupled-cluster singles and doubles (CCSD) levels of theory. For closed-shell molecules, accurate ring-current strengths can be obtained with a reasonable computational cost at the DFT level and with rather small basis sets. For open-shell molecules, it is shown that correlated methods such as MP2 and CCSD might be needed to obtain reliable charge and spin currents. The basis set convergence has to be checked for open-shell molecules by performing calculations with large enough basis sets. The results discussed in the thesis have been published in eight papers. In addition, some previously unpublished results on the ring currents in the endohedral fullerene Sc3C2@C80 and in coronene are presented. It is shown that dynamical effects should be taken into account when modelling magnetic resonance parameters of endohedral metallofullerenes such as Sc3C2@C80. The ring-current strengths in a series of nano-sized hydrocarbon rings are related to static polarizabilities and to H-1 nuclear magnetic resonance (NMR) shieldings. In a case study on the possible aromaticity of a Möbius-shaped [16]annulene we found that, according to the magnetic criterion, the molecule is nonaromatic. The applicability of the GIMIC method to assign the aromatic character of molecules was confirmed in a study on the ring currents in simple monocylic aromatic, homoaromatic, antiaromatic, and nonaromatic hydrocarbons. Case studies on nanorings, hexaphyrins and [n]cycloparaphenylenes show that explicit calculations are needed to unravel the ring-current delocalization pathways in complex multiring molecules. The open-shell implementation of GIMIC was applied in studies on the charge currents and the spin currents in single-ring and bi-ring molecules with open shells. The aromaticity predictions that are made based on the GIMIC results are compared to other aromaticity criteria such as H-1 NMR shieldings and shifts, electric polarizabilities, bond-length alternation, as well as to predictions provided by the traditional Hückel (4n+2) rule and its more recent extensions that account for Möbius twisted molecules and for molecules with open shells.
  • Partanen, Ari (Helsingin yliopisto, 2013)
    Ablative hyperthermia (more than 55 °C) has been used as a stand-alone treatment for accessible solid tumors not amenable to surgery, whereas mild hyperthermia (40-45 °C) has been shown effective as an adjuvant for both radiotherapy and chemotherapy. An optimal mild hyperthermia treatment is noninvasive and spatially accurate, with precise and homogeneous heating limited to the target region. High-intensity focused ultrasound (HIFU) can noninvasively heat solid tumors deep within the human body. Magnetic resonance imaging (MRI) is ideal for HIFU treatment planning and monitoring in real time due to its superior soft-tissue contrast, high spatial imaging resolution, and the ability to measure temperature changes. The combination of MRI and HIFU therapy is known as magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU). Low temperature-sensitive liposomes (LTSLs) release their drug cargo in response to heat (more than 40 °C) and may improve drug delivery to solid tumors when combined with mild hyperthermia. MR-HIFU provides a way to image and control content release from imageable low-temperature sensitive liposomes (iLTSLs). This ability may enable spatiotemporal control over drug delivery - a concept known as drug dose painting. The objectives of this dissertation work were to develop and implement a clinically relevant volumetric mild hyperthermia heating algorithm, to implement and characterize different sonication approaches (multiple foci vs. single focus), and to evaluate the ability to monitor and control heating in real time using MR-HIFU. In addition, the ability of MR-HIFU to induce the release of a clinical-grade cancer drug encapsulated in LTSLs was investigated, and the potential of MR-HIFU mediated mild hyperthermia for clinical translation as an image-guided drug delivery method was explored. Finally, drug and contrast agent release of iLTSLs as well as the ability of MR-HIFU to induce and monitor the content release were examined, and a computational model that simulates MR-HIFU tissue heating and drug delivery was validated. The combination of a multifoci sonication approach and the mild hyperthermia heating algorithm resulted in precise and homogeneous heating limited to the targeted region both in vitro and in vivo. Heating was more spatially confined compared to the use of single focus sonication method. The improvement in spatial control suggests that multifoci heating is a useful tool in MR-HIFU mediated mild hyperthermia applications for clinical oncology. Using the mild hyperthermia heating algorithm, LTSL + MR-HIFU resulted in significantly higher tumor drug concentrations compared to free drug and LTSL alone. This technique has potential for clinical translation as an image-guided drug delivery method. MR-HIFU also enabled real-time monitoring and control of iLTSL content release. Finally, computational models may allow quantitative in silico comparison of different MR-HIFU heating algorithms as well as facilitate therapy planning for this drug delivery technique.
  • Pomoell, Jens (Helsingin yliopisto, 2012)
    Solar eruptions are a consequence of the complex dynamics occurring in the tenuous, hot magnetized plasma that characterizes the solar corona. From a socio-economic viewpoint, solar eruptions can be argued to be the most important manifestation of the magnetic activity of the Sun due to their role as the main drivers of space weather, i.e., conditions in space that can have an adverse impact on space- as well as ground-based technologies such as telecommunication, electric power systems and satellite navigation. The launch of new space-based solar observatories during the past two decades has resulted in a dramatic improvement of the instrumentation monitoring the inner heliosphere. In spite of the advances in the observational capabilities, the physics of the solar eruptions as well as the nature of the various transient large-scale coronal phenomena observationally associated with the eruptions remain elusive. Constructing models capable of simulating the coronal and heliospheric dynamics is a viable path for gaining a more complete understanding of these phenomena. This thesis is concerned with developing a simulation tool based on the magnetohydrodynamic (MHD) description of plasmas and employing it for studying the characteristics of large-scale waves and shocks launched into the solar corona by the lift-off of a solar eruption such as a coronal mass ejection (CME). A particular focus is on discussing the role of large-amplitude waves in producing transient phenomena such as EIT waves and solar energetic particle (SEP) events that are known to appear in conjunction with CMEs. A suite of MHD models of the solar corona are constructed that allow the study of the coronal dynamics in varying environments at several stages of the eruption. For this purpose, novel robust numerical methods for solving the equations of magnetohydrodynamics in orthogonal curvilinear geometries in multiple dimensions are derived, forming the basis of the numerical simulation tool developed for the thesis. The results show that a dynamically intricate global shock front degenerating to a fast-mode MHD wave towards the surface of the Sun is an essential and natural part of the eruption complex that plays a key role in the generation of eruption-related transient phenomena. For instance, the close resemblance between the on-disk signatures produced by the fast-mode wave and EIT waves suggest a wave interpretation of the latter. The simulations also reveal that a highly non-trivial evolution of the shock properties on coronal field lines occurs even for simple coronal conditions, highlighting the need for more sophisticated models of particle acceleration than generally used so far. The results of the thesis are of particular importance for the continuing efforts to construct reliable physics-based models of the inner heliosphere for use in space weather applications.
  • 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.
  • Rantaharju, Jarno (Helsingin yliopisto, 2012)
    The Standard Model of particle physics and the modern understanding of physics at small length scales rests on the foundation of non-Abelian gauge theories. Mapping their behavior at large energies is important in understanding the Standard Model and in extending it to include a wider range of physical phenomena. There is a region in the parameter space of these models where the interaction strength runs to a constant at high energies. These conformal models are useful for explaining the masses of Standard Model particles trough the extended technicolor mechanism. In this thesis I present studies of the conformal window using lattice simulations. This turns out to be a significant challenge in the study non-perturbative quantum physics. We have studied the phase structure of the SU(2) gauge theory coupled to fermions that transform in the fundamental or the adjoint representation of the symmetry group. We have found evidence of large discretization errors and studied them by constructing a Symanzik improved model. The running of the renormalized coupling is greatly affected by improvements in the model. Using the Symanzik improved model we have studied the running of the coupling in the SU(2) gauge theory with fundamental fermions. The models behave as expected with 4 and 10 flavors of fermions. We were unable to distinguish between chirally broken and conformal behavior in the model with 6 fermions. In order to push further into large energy scales we have studied actions with NHYP and HEX smearing. This helps reduce the discretization effects and reduce the corrections in the Symanzik improvement. Using the improved HEX smeared action we have been able to run simulations at larger energy scales than before.
  • Priklopil, Tadeas (Helsingin yliopisto, 2012)
    Speciation theory is undergoing a renaissance period, largely due to the new methods developed in molecular biology as well as advances in the mathematical theory of evolution. In this thesis, I explore mathematical techniques applicable to the evolution of traits relevant to speciation processes. Some of the theory is further developed and is part of a general framework in the research of evolution. In nature, sister species may coexist in close geographical proximity. However, the question as to whether a speciation event has been a local event driven by the interactions (perhaps complex ones) of individuals that affect their survival and reproduction, has not yet been satisfactorily answered. This is the key issue I address in my thesis. The emphasis is given to the role of non-random mating in an environment where individuals experience diversifying ecological selection. Firstly, I investigate the role of assortative mating, and find that assortative mating works against the speciation process in the initial stages of diversification. However, once the population has diversified, ecological and sexual selection drives the population to a state of reproductive isolation. Secondly, I explore a scheme where individuals choose mates according to the level of adaptation of the mate. I find, that when the level of adaptation to the environment depends on the structure of the population in a frequency-dependent manner, the dynamics of the population may be highly complex and even chaotic. Furthermore, this setting does not facilitate reproductive isolation when mating happens across the habitats. However, if mate choice takes into account the survival and reproduction of the progeny, reproductive isolation can be maintained. Finally, some advances are made in the theory of adaptive dynamics, which along with the theory of population genetics, has been a focal tool in this thesis. My contribution to adaptive dynamics is to resolve an open question on the coexistence of similar strategies near so-called singular points. Singular points play a central role in the theory of adaptive dynamics and their existence is essential to a continuous diversification process.
  • Pakkanen, Mikko (Helsingin yliopisto, 2010)
    Frictions are factors that hinder trading of securities in financial markets. Typical frictions include limited market depth, transaction costs, lack of infinite divisibility of securities, and taxes. Conventional models used in mathematical finance often gloss over these issues, which affect almost all financial markets, by arguing that the impact of frictions is negligible and, consequently, the frictionless models are valid approximations. This dissertation consists of three research papers, which are related to the study of the validity of such approximations in two distinct modeling problems. Models of price dynamics that are based on diffusion processes, i.e., continuous strong Markov processes, are widely used in the frictionless scenario. The first paper establishes that diffusion models can indeed be understood as approximations of price dynamics in markets with frictions. This is achieved by introducing an agent-based model of a financial market where finitely many agents trade a financial security, the price of which evolves according to price impacts generated by trades. It is shown that, if the number of agents is large, then under certain assumptions the price process of security, which is a pure-jump process, can be approximated by a one-dimensional diffusion process. In a slightly extended model, in which agents may exhibit herd behavior, the approximating diffusion model turns out to be a stochastic volatility model. Finally, it is shown that when agents' tendency to herd is strong, logarithmic returns in the approximating stochastic volatility model are heavy-tailed. The remaining papers are related to no-arbitrage criteria and superhedging in continuous-time option pricing models under small-transaction-cost asymptotics. Guasoni, Rásonyi, and Schachermayer have recently shown that, in such a setting, any financial security admits no arbitrage opportunities and there exist no feasible superhedging strategies for European call and put options written on it, as long as its price process is continuous and has the so-called conditional full support (CFS) property. Motivated by this result, CFS is established for certain stochastic integrals and a subclass of Brownian semistationary processes in the two papers. As a consequence, a wide range of possibly non-Markovian local and stochastic volatility models have the CFS property.
  • Tanskanen, Antti (Helsingin yliopisto, 2008)
    In cardiac myocytes (heart muscle cells), coupling of electric signal known as the action potential to contraction of the heart depends crucially on calcium-induced calcium release (CICR) in a microdomain known as the dyad. During CICR, the peak number of free calcium ions (Ca) present in the dyad is small, typically estimated to be within range 1-100. Since the free Ca ions mediate CICR, noise in Ca signaling due to the small number of free calcium ions influences Excitation-Contraction (EC) coupling gain. Noise in Ca signaling is only one noise type influencing cardiac myocytes, e.g., ion channels playing a central role in action potential propagation are stochastic machines, each of which gates more or less randomly, which produces gating noise present in membrane currents. How various noise sources influence macroscopic properties of a myocyte, how noise is attenuated and taken advantage of are largely open questions. In this thesis, the impact of noise on CICR, EC coupling and, more generally, macroscopic properties of a cardiac myocyte is investigated at multiple levels of detail using mathematical models. Complementarily to the investigation of the impact of noise on CICR, computationally-efficient yet spatially-detailed models of CICR are developed. The results of this thesis show that (1) gating noise due to the high-activity mode of L-type calcium channels playing a major role in CICR may induce early after-depolarizations associated with polymorphic tachycardia, which is a frequent precursor to sudden cardiac death in heart failure patients; (2) an increased level of voltage noise typically increases action potential duration and it skews distribution of action potential durations toward long durations in cardiac myocytes; and that (3) while a small number of Ca ions mediate CICR, Excitation-Contraction coupling is robust against this noise source, partly due to the shape of ryanodine receptor protein structures present in the cardiac dyad.
  • Miettinen, Pauli (Helsingin yliopisto, 2009)
    Matrix decompositions, where a given matrix is represented as a product of two other matrices, are regularly used in data mining. Most matrix decompositions have their roots in linear algebra, but the needs of data mining are not always those of linear algebra. In data mining one needs to have results that are interpretable -- and what is considered interpretable in data mining can be very different to what is considered interpretable in linear algebra. --- The purpose of this thesis is to study matrix decompositions that directly address the issue of interpretability. An example is a decomposition of binary matrices where the factor matrices are assumed to be binary and the matrix multiplication is Boolean. The restriction to binary factor matrices increases interpretability -- factor matrices are of the same type as the original matrix -- and allows the use of Boolean matrix multiplication, which is often more intuitive than normal matrix multiplication with binary matrices. Also several other decomposition methods are described, and the computational complexity of computing them is studied together with the hardness of approximating the related optimization problems. Based on these studies, algorithms for constructing the decompositions are proposed. Constructing the decompositions turns out to be computationally hard, and the proposed algorithms are mostly based on various heuristics. Nevertheless, the algorithms are shown to be capable of finding good results in empirical experiments conducted with both synthetic and real-world data.
  • Makkonen, Ulla (Helsingin yliopisto, 2014)
    The objective of this thesis was to study the variability of inorganic gases and the chemical composition of particulate matter in ambient air, and to study the comparability of results obtained using novel online techniques and older measurements. In recent decades, emissions of sulphur dioxide have decreased all over Europe and, consequently, ambient concentrations have decreased in Finland. A declining trend was also found in the concentrations of reduced nitrogen during the past years. It was found that, in addition to concentrations in air masses coming from central Europe, the transport pathways of air masses are important factors affecting concentrations in Finland. Decreasing concentrations place greater demands on measurement techniques. To ensure the comparability of the SO2 data obtained earlier, we compared older methods to newer measurement methods. We identified the inorganic main elements, trace elements and polycyclic hydrocarbons in PM1, PM2.5 and PM10 samples collected at the background station in Virolahti, Finland. About 70–80% of the toxic trace elements (lead, cadmium, arsenic and nickel) as well as polycyclic hydrocarbons were found in submicron particles. In practice, all the PAHs found in PM10 were actually present in the PM2.5 fraction. Analysing the PM2.5 or even the PM1 fraction instead of PM10 would prove more beneficial for PAHs and trace elements, because excluding the large particles reduces the effects of the matrix during analysis. During wildfire episodes, the concentrations of the smallest particles (PM1, PM2.5) in particular rose. On the fire days, the potassium concentration rose in all particle fractions, but ammonium and nitrate rose only in PM1. One of the objectives of this thesis was to determine whether the online ion chromatograph with a one-hour time resolution could replace the filter sampling method. We successfully measured the concentrations of gases (HCl, HNO3, HONO, NH3, SO2) and the major inorganic ions in particles (Cl-, NO3-, SO42-, NH4+, Na+, K+, Mg2+, Ca2+) with a MARGA 2S online ion chromatograph in two size ranges in both urban and background environments. We used these short-time resolution measurements to study diurnal cycles of nitrogen-containing gases. In Hyytiälä, we found clear diurnal cycles for all the nitrogen-containing gases, especially in summer, when there is enough sunlight for photochemical reactions and possibly additional emission sources from the boreal forest environment. In winter, however, we found no diurnal cycles in either Hyytiälä or Helsinki, but in spring, diurnal cycles for HONO, HNO3 andNH3 resumed. In Helsinki, the results of the particles were used to study sources using trajectory analysis showing that,although continental aerosols were mostly neutralized, marine aerosols from the Norwegian Sea were not.
  • Ruuskanen, Taina (Helsingin yliopisto, 2009)
    Volatile organic compounds (VOCs) affect atmospheric chemistry and thereafter also participate in the climate change in many ways. The long-lived greenhouse gases and tropospheric ozone are the most important radiative forcing components warming the climate, while aerosols are the most important cooling component. VOCs can have warming effects on the climate: they participate in tropospheric ozone formation and compete for oxidants with the greenhouse gases thus, for example, lengthening the atmospheric lifetime of methane. Some VOCs, on the other hand, cool the atmosphere by taking part in the formation of aerosol particles. Some VOCs, in addition, have direct health effects, such as carcinogenic benzene. VOCs are emitted into the atmosphere in various processes. Primary emissions of VOC include biogenic emissions from vegetation, biomass burning and human activities. VOCs are also produced in secondary emissions from the reactions of other organic compounds. Globally, forests are the largest source of VOC entering the atmosphere. This thesis focuses on the measurement results of emissions and concentrations of VOCs in one of the largest vegetation zones in the world, the boreal zone. An automated sampling system was designed and built for continuous VOC concentration and emission measurements with a proton transfer reaction - mass spectrometer (PTR-MS). The system measured one hour at a time in three-hourly cycles: 1) ambient volume mixing-ratios of VOCs in the Scots-pine-dominated boreal forest, 2) VOC fluxes above the canopy, and 3) VOC emissions from Scots pine shoots. In addition to the online PTR-MS measurements, we determined the composition and seasonality of the VOC emissions from a Siberian larch with adsorbent samples and GC-MS analysis. The VOC emissions from Siberian larch were reported for the fist time in the literature. The VOC emissions were 90% monoterpenes (mainly sabinene) and the rest sesquiterpenes (mainly a-farnesene). The normalized monoterpene emission potentials were highest in late summer, rising again in late autumn. The normalized sesquiterpene emission potentials were also highest in late summer, but decreased towards the autumn. The emissions of mono- and sesquiterpenes from the deciduous Siberian larch, as well as the emissions of monoterpenes measured from the evergreen Scots pine, were well described by the temperature-dependent algorithm. In the Scots-pine-dominated forest, canopy-scale emissions of monoterpenes and oxygenated VOCs (OVOCs) were of the same magnitude. Methanol and acetone were the most abundant OVOCs emitted from the forest and also in the ambient air. Annually, methanol and mixing ratios were of the order of 1 ppbv. The monoterpene and sum of isoprene 2-methyl-3-buten-2-ol (MBO) volume mixing-ratios were an order of magnitude lower. The majority of the monoterpene and methanol emissions from the Scots-pinedominated forest were explained by emissions from Scots pine shoots. The VOCs were divided into three classes based on the dynamics of the summer-time concentrations: 1) reactive compounds with local biological, anthropogenic or chemical sources (methanol, acetone, butanol and hexanal), 2) compounds whose emissions are only temperaturedependent (monoterpenes), 3) long-lived compounds (benzene, acetaldehyde). Biogenic VOC (methanol, acetone, isoprene MBO and monoterpene) volume mixing-ratios had clear diurnal patterns during summer. The ambient mixing ratios of other VOCs did not show this behaviour. During winter we did not observe systematical diurnal cycles for any of the VOCs. Different sources, removal processes and turbulent mixing explained the dynamics of the measured mixing-ratios qualitatively. However, quantitative understanding will require longterm emission measurements of the OVOCs and the use of comprehensive chemistry models. Keywords: Hydrocarbons, VOC, fluxes, volume mixing-ratio, boreal forest
  • Keskitalo, Reijo (Helsingin yliopisto, 2009)
    The first quarter of the 20th century witnessed a rebirth of cosmology, study of our Universe, as a field of scientific research with testable theoretical predictions. The amount of available cosmological data grew slowly from a few galaxy redshift measurements, rotation curves and local light element abundances into the first detection of the cos- mic microwave background (CMB) in 1965. By the turn of the century the amount of data exploded incorporating fields of new, exciting cosmological observables such as lensing, Lyman alpha forests, type Ia supernovae, baryon acoustic oscillations and Sunyaev-Zeldovich regions to name a few. -- CMB, the ubiquitous afterglow of the Big Bang, carries with it a wealth of cosmological information. Unfortunately, that information, delicate intensity variations, turned out hard to extract from the overall temperature. Since the first detection, it took nearly 30 years before first evidence of fluctuations on the microwave background were presented. At present, high precision cosmology is solidly based on precise measurements of the CMB anisotropy making it possible to pinpoint cosmological parameters to one-in-a-hundred level precision. The progress has made it possible to build and test models of the Universe that differ in the way the cosmos evolved some fraction of the first second since the Big Bang. -- This thesis is concerned with the high precision CMB observations. It presents three selected topics along a CMB experiment analysis pipeline. Map-making and residual noise estimation are studied using an approach called destriping. The studied approximate methods are invaluable for the large datasets of any modern CMB experiment and will undoubtedly become even more so when the next generation of experiments reach the operational stage. -- We begin with a brief overview of cosmological observations and describe the general relativistic perturbation theory. Next we discuss the map-making problem of a CMB experiment and the characterization of residual noise present in the maps. In the end, the use of modern cosmological data is presented in the study of an extended cosmological model, the correlated isocurvature fluctuations. Current available data is shown to indicate that future experiments are certainly needed to provide more information on these extra degrees of freedom. Any solid evidence of the isocurvature modes would have a considerable impact due to their power in model selection.
  • 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.
  • Partamies, Noora (Helsingin yliopisto, 2004)