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  • Oksanen, Markku (Helsingin yliopisto, 2013)
    All the fundamental interactions except gravity have been successfully described in the framework of quantum field theory. Construction of a consistent quantum theory of gravity remains a challenge, because the general theory of relativity is not renormalizable. We consider gravitational theories that aim to improve the ultraviolet behavior of general relativity. The main tool of our analysis is the Hamiltonian formulation of theories that possess local (gauge) invariances. Hořava-Lifshitz gravity achieves power-counting renormalizability by assuming that space and time scale anisotropically at high energies. At long distances the theory flows to an effective theory that is relativistically invariant. We propose a generalization of this theory. Motivated by cosmology, the modified F(R) Hořava-Lifshitz gravity is constructed. It retains the renormalizability of the original Hořava-Lifshitz gravity. The Hamiltonian analysis shows that the theory contains two extra degrees of freedom compared to general relativity: one is associated with the lack of relativistic invariance at high energies and another with the presence of a second-order time derivative of the metric in the Lagrangian due to the nonlinearity of the function F(R). The theory is able to describe inflation and dark energy in a unified manner without extra components. For a certain choice of parameters the theory effectively flows to the relativistic F(R) gravity at long distances. Hamiltonian analysis of the recently proposed covariant renormalizable gravity is accomplished. The structure of constraints is discovered to be very complicated, especially for the new version of the theory with improved ultraviolet behavior. Moreover, this theory is found to contain a ghost, a degree of freedom with negative energy, which destabilizes the theory. The Hamiltonian analysis of relativistic higher-derivative gravity is revisited. Conformally invariant Weyl gravity is concluded to be the only theory of this type that could even in principle restrain the existing ghosts, since in all other potentially renormalizable cases the number of ghosts exceeds the number of local invariances. Lastly, we investigate the idea of deriving a gravitational theory by gauging the twisted Poincaré symmetry of noncommutative spacetime.
  • Sajavaara, Timo (Helsingin yliopisto, 2002)
  • Koponen, Jonna (Helsingin yliopisto, 2009)
    Several excited states of Ds and Bs mesons have been discovered in the last six years: BaBar, Cleo and Belle discovered the very narrow states D(s0)*(2317)+- and D(s1)(2460)+- in 2003, and CDF and DO Collaborations reported the observation of two narrow Bs resonances, B(s1)(5830)0 and B*(s2)(5840)0 in 2007. To keep up with experiment, meson excited states should be studied from the theoretical aspect as well. The theory that describes the interaction between quarks and gluons is quantum chromodynamics (QCD). In this thesis the properties of the meson states are studied using the discretized version of the theory - lattice QCD. This allows us to perform QCD calculations from first principles, and "measure" not just energies but also the radial distributions of the states on the lattice. This gives valuable theoretical information on the excited states, as we can extract the energy spectrum of a static-light meson up to D wave states (states with orbital angular momentum L=2). We are thus able to predict where some of the excited meson states should lie. We also pay special attention to the order of the states, to detect possible inverted spin multiplets in the meson spectrum, as predicted by H. Schnitzer in 1978. This inversion is connected to the confining potential of the strong interaction. The lattice simulations can also help us understand the strong interaction better, as the lattice data can be treated as "experimental" data and used in testing potential models. In this thesis an attempt is made to explain the energies and radial distributions in terms of a potential model based on a one-body Dirac equation. The aim is to get more information about the nature of the confining potential, as well as to test how well the one-gluon exchange potential explains the short range part of the interaction.
  • Svedström, Kirsi (Helsingin yliopisto, 2012)
    The interest in wood and its main constituent, cellulose, is growing continuously. This can be explained by the demands of sustainable development and the extending scope of applications enabled by novel materials like nanocrystalline cellulose. Outstanding mechanical properties are one of the main reasons for the usability of wood. However, details on the ultrastructure of wood cell wall are still lacking, and thus also the origin for the mechanical properties is partly unknown. The various properties of plant materials arise from their hierarchical structure. Thus information at several size scales is needed for revealing the structure-function relationships. In this study, the structure of plant cell wall and cellulose based materials was characterized from the micro- to nanometer scale: using x-ray microtomography, the three-dimensional cellular structure was revealed and using x-ray scattering methods, the nanostructure was investigated. In the cell wall, parallel cellulose chains form microfibrils, which are partially crystalline and embedded in an amorphous hemicellulose-lignin matrix. The orientation, width and length of the crystalline parts of microfibrils vary between the plant species and materials. In this thesis, the cellulose structure was characterized in various plant species, and the effects due to drying, chemical pulping and acid hydrolysis were determined. It was found that the properties of the amorphous matrix played a role in all the effects studied. The wide spectrum of the samples, including native cotton, flax, bamboo, various wood species, pulp, microcrystalline and nanofibrillated cellulose (MCC, NFC), enabled interesting comparisons. It was observed, that in tension wood, pulp, MCC, and NFC, the cellulose crystallite width was significantly larger than in native normal wood. The high cellulose content and lack of lignin were typical for all the samples with a larger crystallite width. It was also found that the lateral and longitudinal order of the cellulose chains in crystallites was higher in never-dried wood compared to the corresponding air-dried samples. This indicated that the moisture had impact on the structures formed by crystalline cellulose although the water molecules can not enter the crystallites. One of the objects of the thesis was the study of the cellulose structure of oak from the Swedish warship Vasa. The results gave information on the preservation of the historically important wood throughout the centuries at the bottom of the sea.
  • Airas, Annika (Helsingin yliopisto, 2016)
    Urban waterfront redevelopment is a global trend. Since the 1960s, and the advent of containerization, new commercial and residential developments began to replace the industrial operations that once characterized the waterfronts of port cities. Research to date has largely focused on the redevelopment of seaports in large coastal cities, primarily in a North American context, yet significant changes are also taking place in smaller locations around the globe. In this study, two empirical examples are given of smaller cities, one in Finland and one in Canada, both of which historically served the woodworking industry. As these industries declined and reorganized, the waterfronts they occupied have been redeveloped primarily into residential districts, particularly since the late 1980s. This study takes a new, multidisciplinary approach to waterfront research by advancing the concept of historical distinctiveness and revealing the ways that it is expressed within waterfront planning. While the term distinctiveness is often used in planning documents to refer to the waterfront s historical past, the term remains poorly defined. This study presents the novel concept of historical distinctiveness and introduces a research framework through which it can be understood. In particular, the study pays attention to the content of historical distinctiveness and examines how it is expressed in the contemporary built environment of the formerly industrial waterfronts: Lake Vesijärvi, in Lahti, Finland and in Queensborough, New Westminster, Canada. Historical distinctiveness as defined in this study consists of six interlocking and constantly evolving elements: international historical influences, historic uses of the waterfront and their reflection in local built environments, the waterfront s relation to the city, the multiple historic layers in the built form of the waterfront, comparative differences in architectural history, and varying values. The concept of historical distinctiveness enables local histories and development trajectories to be revealed while widening the understanding of contemporary waterfront cities. Both Lahti and Queensborough are changing quickly and dramatically, which makes it difficult to identify the remaining vestiges of their woodworking past. Furthermore, the appearance and design of new developments reflect a narrow appreciation of their industrial legacy. Planning processes that aim to promote the distinctiveness of historical waterfronts are instead, ironically, ignoring and at times actually erasing truly unique urban histories. This study demonstrates how new rebuilt environments are becoming more similar across sites, while also becoming more similar to non-waterfront areas in cities. Such developments may limit or destroy the use value of these areas while ignoring cultural histories and local identities, thereby limiting options for creating diverse cities. By taking historical distinctiveness into account, cities can increase historical awareness and create possibilities for the future, thereby creating truly distinctive waterfronts.
  • Juntunen, Marianne (Helsingin yliopisto, 2015)
    Chemistry plays an important role in making the future more sustainable and solving the related global issues. Curricula, national and international educational strategies, research literature and chemical industry are all focusing on sustainable development. We need more environmentally literate chemists, chemistry teachers and students future citizens, who are to solve the numerous environmental challenges that face the whole world. The main aim of this design research study was to find out what are the features of holistic and inquiry-based education for sustainable development in chemistry. At the same time, the aim was to foster students environmental literacy, argumentation skills and positive attitudes towards chemistry. Education for sustainable development in chemistry is related to socio-scientific issues, e.g., life-cycle thinking and green chemistry. Theoretical problem-analysis of the study was used to investigate the approaches that are of key importance to the study presented in this dissertation: sustainable development, green chemistry, the life-cycles of different products, environmental literacy, socio-scientific education, and the pedagogical methods of inquiry-based learning and argumentation. The empirical design phase sought an answer to the main research question: What are the main features of holistic and inquiry-based education for sustainable development in chemistry? The main focus of the research was in teaching life-cycle analysis, which is one of the key elements in the Finnish national curriculum. The design research project constituted of three phases, which were conducted during the years 2010 2014. The first empirical phase was conducted in four chemistry teachers in-service training courses. During these courses, a total of 20 chemistry teachers created new inquiry-based methods for teaching life-cycle analysis in chemistry. This development process was based on theoretical problem analysis. The second empirical phase focused on creating a collaboratively-developed design solution based on the teachers concepts and the effects of this solution. The participants in this second phase were 105 9th grade students, whose environmental literacy, argumentation skills and attitudes towards chemistry learning were evaluated. The third phase was theoretical. It consisted of comparing the gained empirical knowledge to theoretical literature in order to answer the main research question. The methods of data analysis included content analysis of texts, semi-structured interviews and quantitative surveys. The validity of the results of the conducted cyclic design research project is enhanced by theoretical literature analysis, methodological triangulation, researcher triangulation, the testing of the developed teaching concept in authentic environments and the systematic, visualised documentation of the design phases. The design phases resulted in three types of knowledge: 1) new chemistry teaching concepts for sustainability education that use life-cycle thinking and inquiry-based learning methods, and a collaboratively-developed design solution (Article I), 2) knowledge about how inquiry-based learning of life-cycle analysis affects students environmental literacy, argumentation skills and attitudes towards chemistry (Articles II and III) and 3) domain knowledge about holistic and inquiry-based education for sustainable development in chemistry (Article IV). Holistic and inquiry-based education for sustainable development in chemistry includes interdisciplinary and socio-scientific issues. Socio-constructivist and contextual chemistry education is bound to societal actors and co-operational, real-life activities. Learning occurs in social interaction, through argumentation and self-reflection, for example. The students themselves may choose the focus of inquiry, and it may relate to raw materials, consumer products, food substances or water, for example. As the knowledge of chemistry is combined with possibilities for societal action, the importance of chemistry becomes apparent to the students. They gain competence to act towards building a more sustainable future. The improved scientific and ecological argumentation skills reflect their environmental literacy and competence in societal thinking. The holistic and inquiry-based chemistry education presented in this dissertation supports versatile studying and citizenship skills in a new way. It motivates students to study chemistry and guides them to take sustainable development into account. Education for sustainable development is needed at all school levels. The approaches presented in this study may be applied on all levels of education. The results may be used to promote sustainable development in the planning of chemistry education and the education of chemistry teachers. Keywords: chemistry education, sustainable development, green chemistry, teaching concepts, design research
  • Alanen, Janne (Helsingin yliopisto, 2012)
    Gauge theories are used to describe interactions between the elementary particles of the standard model and beyond standard model theories. In the regime where interactions are strong perturbative methods cannot be used. Thus the non-perturbative part is generally studied by using lattice simulations and effective field theories. However a new method for exploring the non-perturbative part is the AdS/CFT duality that relates a specific string theory and a conformal field theory. In this thesis, the AdS/CFT duality is generalized to non-conformal gauge theories and its implications are studied. In particular, a holographic model for studying various large-N gauge theories is introduced.
  • Keränen, Ville (Helsingin yliopisto, 2011)
    Superfluidity is perhaps one of the most remarkable observed macroscopic quantum effect. Superfluidity appears when a macroscopic number of particles occupies a single quantum state. Using modern experimental techniques one dark solitons) and vortices. There is a large literature on theoretical work studying the properties of such solitons using semiclassical methods. This thesis describes an alternative method for the study of superfluid solitons. The method used here is a holographic duality between a class of quantum field theories and gravitational theories. The classical limit of the gravitational system maps into a strong coupling limit of the quantum field theory. We use a holographic model of superfluidity to study solitons in these systems. One particularly appealing feature of this technique is that it allows us to take into account finite temperature effects in a large range of temperatures.
  • Stenlund, Mikko (Helsingin yliopisto, 2006)
    We study a Hamiltonian describing a pendulum coupled with several anisochronous oscillators, giving a simple construction of unstable KAM tori and their stable and unstable manifolds for analytic perturbations. When the coupling takes place through an even trigonometric polynomial in the angle variables, we extend analytically the solutions of the equations of motion, order by order in the perturbation parameter, to a large neighbourhood of the real line representing time. Subsequently, we devise an asymptotic expansion for the splitting (matrix) associated with a homoclinic point. This expansion consists of contributions that are manifestly exponentially small in the limit of vanishing gravity, by a shift-of-countour argument. Hence, we infer a similar upper bound for the splitting itself. In particular, the derivation of the result does not call for a tree expansion with explicit cancellation mechanisms.
  • Hirvonen, Åsa (Helsingin yliopisto, 2009)
    This thesis studies homogeneous classes of complete metric spaces. Over the past few decades model theory has been extended to cover a variety of nonelementary frameworks. Shelah introduced the abstact elementary classes (AEC) in the 1980s as a common framework for the study of nonelementary classes. Another direction of extension has been the development of model theory for metric structures. This thesis takes a step in the direction of combining these two by introducing an AEC-like setting for studying metric structures. To find balance between generality and the possibility to develop stability theoretic tools, we work in a homogeneous context, thus extending the usual compact approach. The homogeneous context enables the application of stability theoretic tools developed in discrete homogeneous model theory. Using these we prove categoricity transfer theorems for homogeneous metric structures with respect to isometric isomorphisms. We also show how generalized isomorphisms can be added to the class, giving a model theoretic approach to, e.g., Banach space isomorphisms or operator approximations. The novelty is the built-in treatment of these generalized isomorphisms making, e.g., stability up to perturbation the natural stability notion. With respect to these generalized isomorphisms we develop a notion of independence. It behaves well already for structures which are omega-stable up to perturbation and coincides with the one from classical homogeneous model theory over saturated enough models. We also introduce a notion of isolation and prove dominance for it.
  • Hagros, Annika (Helsingin yliopisto, 2006)
    A new rock mass classification scheme, the Host Rock Classification system (HRC-system) has been developed for evaluating the suitability of volumes of rock mass for the disposal of high-level nuclear waste in Precambrian crystalline bedrock. To support the development of the system, the requirements of host rock to be used for disposal have been studied in detail and the significance of the various rock mass properties have been examined. The HRC-system considers both the long-term safety of the repository and the constructability in the rock mass. The system is specific to the KBS-3V disposal concept and can be used only at sites that have been evaluated to be suitable at the site scale. By using the HRC-system, it is possible to identify potentially suitable volumes within the site at several different scales (repository, tunnel and canister scales). The selection of the classification parameters to be included in the HRC-system is based on an extensive study on the rock mass properties and their various influences on the long-term safety, the constructability and the layout and location of the repository. The parameters proposed for the classification at the repository scale include fracture zones, strength/stress ratio, hydraulic conductivity and the Groundwater Chemistry Index. The parameters proposed for the classification at the tunnel scale include hydraulic conductivity, Q´ and fracture zones and the parameters proposed for the classification at the canister scale include hydraulic conductivity, Q´, fracture zones, fracture width (aperture + filling) and fracture trace length. The parameter values will be used to determine the suitability classes for the volumes of rock to be classified. The HRC-system includes four suitability classes at the repository and tunnel scales and three suitability classes at the canister scale and the classification process is linked to several important decisions regarding the location and acceptability of many components of the repository at all three scales. The HRC-system is, thereby, one possible design tool that aids in locating the different repository components into volumes of host rock that are more suitable than others and that are considered to fulfil the fundamental requirements set for the repository host rock. The generic HRC-system, which is the main result of this work, is also adjusted to the site-specific properties of the Olkiluoto site in Finland and the classification procedure is demonstrated by a test classification using data from Olkiluoto. Keywords: host rock, classification, HRC-system, nuclear waste disposal, long-term safety, constructability, KBS-3V, crystalline bedrock, Olkiluoto
  • Eskelä, Elina (Helsingin yliopisto, 2015)
    Cities are striving to attract and retain talented workers in order to increase their competitiveness in the new economy, which is highly dependent on innovation and knowledge. Residential satisfaction has been identified as a key determinant of whether a person stays or moves to another location. However, given the tendency to focus on the housing of immigrant groups with a lower socio-economic status, the factors that affect the residential satisfaction of skilled migrants remain understudied. This article-based dissertation in the field of urban geography examines the determinants of residential satisfaction among skilled migrants living in the Helsinki metropolitan area (HMA), Finland. The research setting is intended to maximise the cultural and socio-economic as well as locational diversity within the limits of recognised skilled migrant groups. The analysis focuses on how the interplay between individuals norms and the situational conditions is manifested when immigrants assess a single housing market, the HMA. The study is qualitative in nature and draws on 70 semi-structured interviews with skilled migrants and with experts on migration and housing in the city region. Despite the cultural, socioeconomic and locational heterogeneity of the interviewees, their experiences of housing in the HMA were notably similar: the uppermost assessment was that it is expensive, cramped and uniform. On the other hand, they appreciated the overall safety and functionality of the city region, as well as the natural environment: the predominant influence, for them, is the family life cycle rather than the urban amenities that are often assumed to be highly important for the creative class . The results also show that homeownership is not a simple indicator of the intention to stay in or leave the region, which contradicts earlier findings on ethnic-minority housing. The study underlines the importance of the social environment in creating residential satisfaction among skilled migrants. Whereas earlier studies revealed the essential nature of social networks and personal trajectories in the location decisions of skilled workers, the results of this study indicate that the supply of local, neighbourhood-based social ties is particularly limited in the case of the HMA, and that this has a negative impact on the residential satisfaction of skilled migrants. Furthermore, the structural element of housing seemed to have an effect on local social ties: among international students the extent of such ties varied according to the housing form. Although many skilled migrants are in a good socio-economic position, they are not immune to problems related to finding suitable housing. Housing availability, quality and affordability are therefore significant factors in enhancing residential satisfaction among such groups. Furthermore, as local social ties serve a mediating role with regard to the residential area as well as to society, the formation of such ties would promote the integration of migrants. These aspects of housing should be acknowledged in the strategies of cities wishing to accommodate and retain global talent. Keywords: skilled migrants, housing, residential satisfaction, social ties, Helsinki metropolitan area
  • Lehtipalo, Katrianne (Helsingin yliopisto, 2011)
    Aerosol particles deteriorate air quality, atmospheric visibility and our health. They affect the Earth s climate by absorbing and scattering sunlight, forming clouds, and also via several feed-back mechanisms. The net effect on the radiative balance is negative, i.e. cooling, which means that particles counteract the effect of greenhouse gases. However, particles are one of the poorly known pieces in the climate puzzle. Some of the airborne particles are natural, some anthropogenic; some enter the atmosphere in particle form, while others form by gas-to-particle conversion. Unless the sources and dynamical processes shaping the particle population are quantified, they cannot be incorporated into climate models. The molecular level understanding of new particle formation is still inadequate, mainly due to the lack of suitable measurement techniques to detect the smallest particles and their precursors. This thesis has contributed to our ability to measure newly formed particles. Three new condensation particle counter applications for measuring the concentration of nano-particles were developed. The suitability of the methods for detecting both charged and electrically neutral particles and molecular clusters as small as 1 nm in diameter was thoroughly tested both in laboratory and field conditions. It was shown that condensation particle counting has reached the size scale of individual molecules, and besides measuring the concentration they can be used for getting size information. In addition to atmospheric research, the particle counters could have various applications in other fields, especially in nanotechnology. Using the new instruments, the first continuous time series of neutral sub-3 nm particle concentrations were measured at two field sites, which represent two different kinds of environments: the boreal forest and the Atlantic coastline, both of which are known to be hot-spots for new particle formation. The contribution of ions to the total concentrations in this size range was estimated, and it could be concluded that the fraction of ions was usually minor, especially in boreal forest conditions. Since the ionization rate is connected to the amount of cosmic rays entering the atmosphere, the relative contribution of neutral to charged nucleation mechanisms extends beyond academic interest, and links the research directly to current climate debate.
  • Karesoja, Mikko (Helsingin yliopisto, 2015)
    In this study several inorganic-organic hybrids and multiresponsive hybrid polymers were prepared and characterised in detail. Especially the focus has been on stimuli responsive materials but also on nanocomposites based on modified montmorillonite clay. Furthermore thin SiO2-capillaries were modified for electrophoretic separations. In all cases different controlled radical polymerisation techniques have been used. The modification of montmorillonite clay was conducted by surface initiated atom transfer polymerisation. Clay was grafted with random copolymer of butyl acrylate and methyl methacrylate and the modified clay was further mixed with a matrix polymer with the same chemical composition to create nanocomposite films. The relation of the nanocomposite structure to its mechanical properties was in the main focus. The extent of exfoliation of the clay in the composite films clearly affected mechanical properties. Montmorillonite clay was also grafted with pH- and thermoresponsive poly(2-dimethylaminoethyl methacrylate). The thermoresponsive properties of the resulting hybrid materials were compared to similar homopolymer. The inner walls of thin silica capillaries were grafted with a cationic polymer, poly([2-(methacryloyl)oxyethyl]trimethylammonium chloride) (PMOTAC). These capillaries were further used in capillary electrophoresis to separate standard proteins, different β-blockers and low-density as well as high density lipoproteins. The separation of the analytes was not possible with bare SiO2-capillaries but with polymer coated capillaries good separation of the analytes was achieved. Hybrid materials based on mesoporous silica particles grafted with poly(N-vinylcaprolactam-b-polyethylene oxide) (PVCL-b-PEO) were synthesised. The challenging synthesis of these hybrids was performed as a combination of surface initiated atom transfer polymerisation and click reactions. Thermal behaviour and the colloidal stability of these hybrid particles were studied. The role of the PEO block in the colloidal stability of the particles was crucial. Finally, multiresponsive hybrid block copolymers based on N-vinylcaprolactam and 2-dimethylaminoethyl methacrylate was prepared. The thermal properties of these block copolymers can be tuned by varying the chain length of PVCL block. On the other hand the thermal behaviour of PDMAEMA block is highly dependent on the environmental conditions like pH and ionic strength.
  • Sillanpää, Ilkka (Helsingin yliopisto, 2008)
    In this dissertation we study the interaction between Saturn's moon Titan and the magnetospheric plasma and magnetic field. The method of research is a three-dimensional computer simulation model, that is used to simulate this interaction. The simulation model used is a hybrid model. Hybrid models enable individual tracking or tracing of ions and also take into account the particle motion in the propagation of the electromagnetic fields. The hybrid model has been developed at the Finnish Meteorological Institute. This thesis gives a general description of the effects that the solar wind has on Earth and other planets of our solar system. Planetary satellites can also have similar interactions with the solar wind but also with the plasma flows of planetary magnetospheres. Titan is clearly the largest among the satellites of Saturn and also the only known satellite with a dense atmosphere. It is the atmosphere that makes Titan's plasma interaction with the magnetosphere of Saturn so unique. Nevertheless, comparisons with the plasma interactions of other solar system bodies are valuable. Detecting charged plasma particles requires in situ measurements obtainable through scientific spacecraft. The Cassini mission has been one of the most remarkable international efforts in space science. Since 2004 the measurements and images obtained from instruments onboard the Cassini spacecraft have increased the scientific knowledge of Saturn as well as its satellites and magnetosphere in a way no one was probably able to predict. The current level of science on Titan is practically unthinkable without the Cassini mission. Many of the observations by Cassini instrument teams have influenced this research both the direct measurements of Titan as well as observations of its plasma environment. The theoretical principles of the hybrid modelling approach are presented in connection to the broader context of plasma simulations. The developed hybrid model is described in detail: e.g. the way the equations of the hybrid model are solved is shown explicitly. Several simulation techniques, such as the grid structure and various boundary conditions, are discussed in detail as well. The testing and monitoring of simulation runs is presented as an essential routine when running sophisticated and complex models. Several significant improvements of the model, that are in preparation, are also discussed. A main part of this dissertation are four scientific articles based on the results of the Titan model. The Titan model developed during the course of the Ph.D. research has been shown to be an important tool to understand Titan's plasma interaction. One reason for this is that the structures of the magnetic field around Titan are very much three-dimensional. The simulation results give a general picture of the magnetic fields in the vicinity of Titan. The magnetic fine structure of Titan's wake as seen in the simulations seems connected to Alfvén waves an important wave mode in space plasmas. The particle escape from Titan is also a major part of these studies. Our simulations show a bending or turning of Titan's ionotail that we have shown to be a direct result of the basic principles in plasma physics. Furthermore, the ion flux from the magnetosphere of Saturn into Titan's upper atmosphere has been studied. The modelled ion flux has asymmetries that would likely have a large impact in the heating in different parts of Titan's upper atmosphere.
  • Pellinen, Riikka (Helsingin yliopisto, 2001)
  • Lallo, Marko (Helsingin yliopisto, 2010)
    This research has been prompted by an interest in the atmospheric processes of hydrogen. The sources and sinks of hydrogen are important to know, particularly if hydrogen becomes more common as a replacement for fossil fuel in combustion. Hydrogen deposition velocities (vd) were estimated by applying chamber measurements, a radon tracer method and a two-dimensional model. These three approaches were compared with each other to discover the factors affecting the soil uptake rate. A static-closed chamber technique was introduced to determine the hydrogen deposition velocity values in an urban park in Helsinki, and at a rural site at Loppi. A three-day chamber campaign to carry out soil uptake estimation was held at a remote site at Pallas in 2007 and 2008. The atmospheric mixing ratio of molecular hydrogen has also been measured by a continuous method in Helsinki in 2007 - 2008 and at Pallas from 2006 onwards. The mean vd values measured in the chamber experiments in Helsinki and Loppi were between 0.0 and 0.7 mm s-1. The ranges of the results with the radon tracer method and the two-dimensional model were 0.13 - 0.93 mm s-1 and 0.12 - 0.61 mm s-1, respectively, in Helsinki. The vd values in the three-day campaign at Pallas were 0.06 - 0.52 mm s-1 (chamber) and 0.18 - 0.52 mm s-1 (radon tracer method and two-dimensional model). At Kumpula, the radon tracer method and the chamber measurements produced higher vd values than the two-dimensional model. The results of all three methods were close to each other between November and April, except for the chamber results from January to March, while the soil was frozen. The hydrogen deposition velocity values of all three methods were compared with one-week cumulative rain sums. Precipitation increases the soil moisture, which decreases the soil uptake rate. The measurements made in snow seasons showed that a thick snow layer also hindered gas diffusion, lowering the vd values. The H2 vd values were compared to the snow depth. A decaying exponential fit was obtained as a result. During a prolonged drought in summer 2006, soil moisture values were lower than in other summer months between 2005 and 2008. Such conditions were prevailing in summer 2006 when high chamber vd values were measured. The mixing ratio of molecular hydrogen has a seasonal variation. The lowest atmospheric mixing ratios were found in the late autumn when high deposition velocity values were still being measured. The carbon monoxide (CO) mixing ratio was also measured. Hydrogen and carbon monoxide are highly correlated in an urban environment, due to the emissions originating from traffic. After correction for the soil deposition of H2, the slope was 0.49±0.07 ppb (H2) / ppb (CO). Using the corrected hydrogen-to-carbon-monoxide ratio, the total hydrogen load emitted by Helsinki traffic in 2007 was 261 t (H2) a-1. Hydrogen, methane and carbon monoxide are connected with each other through the atmospheric methane oxidation process, in which formaldehyde is produced as an important intermediate. The photochemical degradation of formaldehyde produces hydrogen and carbon monoxide as end products. Examination of back-trajectories revealed long-range transportation of carbon monoxide and methane. The trajectories can be grouped by applying cluster and source analysis methods. Thus natural and anthropogenic emission sources can be separated by analyzing trajectory clusters.