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  • Keceli, Asli (Helsingin yliopisto, 2015)
    The Standard Model of particle physics (SM) is a gauge field theory that provides a very successful description of the electromagnetic, weak and strong interactions among the elementary particles. It is in very good agreement with the precision measurements and the list of all the fundamental particles predicted by the model was completed with the discovery of the last missing piece, the Higgs boson, at the LHC in 2012. However, it is believed to be valid up to a certain energy scale and widely considered as a low-scale approximation of a more fundamental theory due to some theoretical and phenomenological issues appearing in the model. Among many alternatives, supersymmetry is considered as the most prominent candidate for new physics beyond the SM. Supersymmetry relates two different classes of the particles known as fermions and bosons. The simplest straightforward supersymmetrization of the SM is named as minimal supersymmetric Standard Model (MSSM) where minimal set of new supersymmetric particles is introduced as superpartners of the Standard Model particles. It is the most studied low-scale supersymmetric model since it has very appealing features such as containing a dark matter candidate and providing a solution to the naturalness problem of the SM. After the Higgs discovery, the parameter space of the model has been investigated in great detail and it has been observed that the measured Higgs mass can be achieved only for the parameter regions which generate a severe fine-tuning. Such large fine-tuning can be alleviated by extending the minimal field content of the model via a singlet and/or a triplet. In this thesis, we discuss the triplet extension of the supersymmetric Standard Model where the MSSM field content is enlarged by introducing a triplet chiral superfield with zero hypercharge. The first part of the thesis contains an overview of the SM and the second part is dedicated to the general features of supersymmetry. After discussing aspects of the MSSM in the third part, we discuss the triplet extended supersymmetric Standard Model where we investigate the implications of the triplet on the Higgs phenomenology. We show that the measured mass of the Higgs boson can be achieved in this model without requiring heavy third generation squarks and/or large squark mixing parameters which reduce the amount of the required fine-tuning. Afterwards, we study the charged Higgs sector where a triplet scalar field with non-zero vacuum expectation value leads to h±iZW∓ coupling at tree level. We discuss how this coupling alters the charged Higgs decay and production channels at the LHC.
  • Lignell, Hanna (Helsingin yliopisto, 2014)
    In this thesis, fundamentally and atmospherically relevant species, their heterogeneous chemistry, and photolytic processing in multiple phases are explored both experimentally and computationally, providing important new insights and mechanistic understanding of these complicated systems. HArF is a covalently bonded neutral ground-state molecule of argon that is found to form at very low temperatures. This thesis explores the HArF low temperature formation mechanism and kinetics, and discusses the effect of the environment to the formation. In the next part, a computational study of an atmospherically relevant molecule N2O4 and its isomerization and ionization on model ice and silica surfaces is presented. N2O4 is known to produce HONO, which is a major source of atmospheric OH, an important atmospheric oxidant. The isomerization mechanism is found to be connected to the dangling surface hydrogen atoms at both surfaces, and we suggest that this mechanism could be expanded to other atmospherically relevant surfaces as well. Atmospheric aerosols play a critical role in controlling climate, driving chemical reactions in the atmosphere, acting as surfaces catalyzing heterogeneous reactions, and contributing to air pollution problems and indoor air quality issues. Low-volatility organic compounds that are produced in the oxidation of biogenic and anthropogenic Volatile Organic Compounds (VOC s) are known collectively as Secondary Organic Aerosol (SOA). In this thesis, a comprehensive investigation of aqueous photochemistry of cis-pinonic acid, a common product of ozonolysis of α-pinene (an SOA precursor) is presented. Various experimental techniques are used to study the kinetics, photolysis rates, quantum yields, and photolysis products, and computational methods are used to explore the photolysis mechanisms. Atmospheric implications and importance of aqueous photolysis vs. OH-mediated aging is discussed. The viscosity effects on SOA chemistry are then explored by a novel approach where an environmentally relevant probe molecule 2,4-dinitrophenol is embedded directly inside the SOA matrix, and its photochemistry is studied at different temperatures and compared to reaction efficiency in other reaction media (octanol and water). It is observed that decreasing temperature significantly slows down the photochemical process in the SOA matrix, and this behavior is ascribed to increasing viscosity of the SOA material.
  • Isoniemi, Esa (Helsingin yliopisto, 2003)
  • Elbra, Tiiu (Helsingin yliopisto, 2011)
    Physical properties provide valuable information about the nature and behavior of rocks and minerals. The changes in rock physical properties generate petrophysical contrasts between various lithologies, for example, between shocked and unshocked rocks in meteorite impact structures or between various lithologies in the crust. These contrasts may cause distinct geophysical anomalies, which are often diagnostic to their primary cause (impact, tectonism, etc). This information is vital to understand the fundamental Earth processes, such as impact cratering and associated crustal deformations. However, most of the present day knowledge of changes in rock physical properties is limited due to a lack of petrophysical data of subsurface samples, especially for meteorite impact structures, since they are often buried under post-impact lithologies or eroded. In order to explore the uppermost crust, deep drillings are required. This dissertation is based on the deep drill core data from three impact structures: (i) the Bosumtwi impact structure (diameter 10.5 km, 1.07 Ma age; Ghana), (ii) the Chesapeake Bay impact structure (85 km, 35 Ma; Virginia, U.S.A.), and (iii) the Chicxulub impact structure (180 km, 65 Ma; Mexico). These drill cores have yielded all basic lithologies associated with impact craters such as post-impact lithologies, impact rocks including suevites and breccias, as well as fractured and unfractured target rocks. The fourth study case of this dissertation deals with the data of the Paleoproterozoic Outokumpu area (Finland), as a non-impact crustal case, where a deep drilling through an economically important ophiolite complex was carried out. The focus in all four cases was to combine results of basic petrophysical studies of relevant rocks of these crustal structures in order to identify and characterize various lithologies by their physical properties and, in this way, to provide new input data for geophysical modellings. Furthermore, the rock magnetic and paleomagnetic properties of three impact structures, combined with basic petrophysics, were used to acquire insight into the impact generated changes in rocks and their magnetic minerals, in order to better understand the influence of impact. The obtained petrophysical data outline the various lithologies and divide rocks into four domains. Based on target lithology the physical properties of the unshocked target rocks are controlled by mineral composition or fabric, particularly porosity in sedimentary rocks, while sediments result from diverse sedimentation and diagenesis processes. The impact rocks, such as breccias and suevites, strongly reflect the impact formation mechanism and are distinguishable from the other lithologies by their density, porosity and magnetic properties. The numerous shock features resulting from melting, brecciation and fracturing of the target rocks, can be seen in the changes of physical properties. These features include an increase in porosity and subsequent decrease in density in impact derived units, either an increase or a decrease in magnetic properties (depending on a specific case), as well as large heterogeneity in physical properties. In few cases a slight gradual downward decrease in porosity, as a shock-induced fracturing, was observed. Coupled with rock magnetic studies, the impact generated changes in magnetic fraction the shock-induced magnetic grain size reduction, hydrothermal- or melting-related magnetic mineral alteration, shock demagnetization and shock- or temperature-related remagnetization can be seen. The Outokumpu drill core shows varying velocities throughout the drill core depending on the microcracking and sample conditions. This is similar to observations by Kern et al., (2009), who also reported the velocity dependence on anisotropy. The physical properties are also used to explain the distinct crustal reflectors as observed in seismic reflection studies in the Outokumpu area. According to the seismic velocity data, the interfaces between the diopside-tremolite skarn layer and either serpentinite, mica schist or black schist are causing the strong seismic reflectivities.
  • Kohout, Tomas (Helsingin yliopisto, 2009)
    Together with cosmic spherules, interplanetary dust particles and lunar samples returned by Apollo and Luna missions, meteorites are the only source of extraterrestrial material on Earth. The physical properties of meteorites, especially their magnetic susceptibility, bulk and grain density, porosity and paleomagnetic information, have wide applications in planetary research and can reveal information about origin and internal structure of asteroids. Thus, an expanded database of meteorite physical properties was compiled with new measurements done in meteorite collections across Europe using a mobile laboratory facility. However, the scale problem may bring discrepancies in the comparison of asteroid and meteorite properties. Due to inhomogenity, the physical properties of meteorites studied on a centimeter or millimeter scale may differ from those of asteroids determined on kilometer scales. Further difference may arise from shock effects, space and terrestrial weathering and from difference in material properties at various temperatures. Close attention was given to the reliability of the paleomagnetic and paleointensity information in meteorites and the methodology to test for magnetic overprints was prepared and verified.
  • Tala, Suvi (Helsingin yliopisto, 2015)
    A central part of the enculturation of new scientists in the natural sciences takes place in poorly understood apprentice master settings: potential expert researchers learn about success in science by doing science as members of research groups. What makes learning in such settings challenging is that a central part of the expertise they are attempting to achieve is tacit: the ideas guiding scientific knowledge-building are embodied in its practices and are nowadays rarely articulated. This interdisciplinary study develops a naturalistic view concerning scientific knowledge construction and justification and what is learned in those processes, in close cooperation with practitioners and by reflection on their actual practices. Such a viewpoint guides developing the expertise education of scientists. Another goal of the study is to encourage science education at every level to reflect as much as possible the epistemological aspects of doing science that practising scientists can also agree upon. The theoretical part of the dissertation focuses on those features of experimentation and modelling that the viewpoints of scientific practices suggest are essential but which are not addressed in the traditional views of science studies and, as a consequence, in science education. Theoretical ideas are tested and deepened in the empirical part, which concerns nanoscience. The developed contextualized method supports scientists in reflecting on their shared research practices and articulating those reflections in the questionnaire and interview. Contrary to traditional views, physical knowledge is understood to progress through the technoscientific design process, aiming at tightening the mutually developing conceptual and material control over the physical world. The products of the design process are both understanding about scientific phenomena and the means to study them, which means constructing and controlling a laboratory phenomenon, created in a laboratory in the same design process that produces the understanding about its functioning. These notions suggest the revision of what exactly is achieved by science and on what kind of basis, which indeed moves the epistemological views of science towards a viewpoint recognizable to its practitioners. Nowadays, technoscientific design is increasingly embodied in simulative modelling, mediating between the experimental reality and its theoretical framework. Such modelling is neither a part or continuation of theorizing as most literature considers modelling, nor it is only a bare means to analyse experimental data, but a partly independent and flexible method of generating our understanding of the world. Because the rapid development of modelling technology alters the evidential basis of science, a new kind of expertise is needed. The entry to the physical reality provided by generative modelling differs epistemologically and cognitively, from traditional methodological approaches. The expertise developed in such modelling provides scientists with new kinds of possibilities. For young scientists success and scientific and technological progress, this expertise is worth understanding.
  • Nousiainen, Maija (Helsingin yliopisto, 2012)
    In physics teacher education the use of graphical knowledge-representation tools like concept maps are often used because they are known to support the formation of organised knowledge. It is widely assumed that certain structural characteristics of concept maps can be connected to the usefulness of content. In order to study this relationship, the concept maps made by pre-service physics teachers are examined here. The design principles of the concept maps are based on quantitative experiments and modelling as the basic procedures in physics concept formation. The approach discussed here is informed by the recent cognitively oriented ideas of knowledge organisation around basic knowledge-organisation patterns and how they form the basis of more complex concept networks. The epistemic plausibility of justifications written in links is evaluated by using a four-level classification introduced here. The new method generalises and widens the existing approaches which use concept maps in representing the learners knowledge, and which also use concept maps for research purposes. Therefore, this thesis presents some novel theoretical constructs for analysis and discusses empirical results by using these new constructs at length, in order to show the advantages which the new theoretical aspects offer. Modelling of the data shows that such a concept-mapping technique supports students conceptual understanding. Also their usefulness in making plans for teaching is identified through modelling the flux of information which the relational structure of the map represents.
  • Noschis, Elias (Helsingin yliopisto, 2006)
    The TOTEM experiment at the LHC will measure the total proton-proton cross-section with a precision better than 1%, elastic proton scattering over a wide range in momentum transfer -t= p^2 theta^2 up to 10 GeV^2 and diffractive dissociation, including single, double and central diffraction topologies. The total cross-section will be measured with the luminosity independent method that requires the simultaneous measurements of the total inelastic rate and the elastic proton scattering down to four-momentum transfers of a few 10^-3 GeV^2, corresponding to leading protons scattered in angles of microradians from the interaction point. This will be achieved using silicon microstrip detectors, which offer attractive properties such as good spatial resolution (<20 um), fast response (O(10ns)) to particles and radiation hardness up to 10^14 "n"/cm^2. This work reports about the development of an innovative structure at the detector edge reducing the conventional dead width of 0.5-1 mm to 50-60 um, compatible with the requirements of the experiment.
  • Tirri, Henry (Helsingin yliopisto, 1997)
  • Kulikov, Vadim (Helsingin yliopisto, 2011)
    The most prominent objective of the thesis is the development of the generalized descriptive set theory, as we call it. There, we study the space of all functions from a fixed uncountable cardinal to itself, or to a finite set of size two. These correspond to generalized notions of the universal Baire space (functions from natural numbers to themselves with the product topology) and the Cantor space (functions from natural numbers to the {0,1}-set) respectively. We generalize the notion of Borel sets in three different ways and study the corresponding Borel structures with the aims of generalizing classical theorems of descriptive set theory or providing counter examples. In particular we are interested in equivalence relations on these spaces and their Borel reducibility to each other. The last chapter shows, using game-theoretic techniques, that the order of Borel equivalence relations under Borel reduciblity has very high complexity. The techniques in the above described set theoretical side of the thesis include forcing, general topological notions such as meager sets and combinatorial games of infinite length. By coding uncountable models to functions, we are able to apply the understanding of the generalized descriptive set theory to the model theory of uncountable models. The links between the theorems of model theory (including Shelah's classification theory) and the theorems in pure set theory are provided using game theoretic techniques from Ehrenfeucht-Fraïssé games in model theory to cub-games in set theory. The bottom line of the research declairs that the descriptive (set theoretic) complexity of an isomorphism relation of a first-order definable model class goes in synch with the stability theoretical complexity of the corresponding first-order theory. The first chapter of the thesis has slightly different focus and is purely concerned with a certain modification of the well known Ehrenfeucht-Fraïssé games. There we (me and my supervisor Tapani Hyttinen) answer some natural questions about that game mainly concerning determinacy and its relation to the standard EF-game
  • Tyynelä, Jani (Helsingin yliopisto, 2011)
    In remote-sensing studies, particles that are comparable to the wavelength exhibit characteristic features in electromagnetic scattering, especially in the degree of linear polarization. These features vary with the physical properties of the particles, such as shape, size, refractive index, and orientation. In the thesis, the direct problem of computing the unknown scattered quantities using the known properties of the particles and the incident radiation is solved at both optical and radar spectral regions in a unique way. The internal electromagnetic fields of wavelength-scale particles are analyzed by using both novel and established methods to show how the internal fields are related to the scattered fields in the far zone. This is achieved by using the tools and methods that were developed specifically to reveal the internal field structure of particles and to study the mechanisms that relate the structure to the scattering characteristics of those particles. It is shown that, for spherical particles, the internal field is a combination of a forward propagating wave with the apparent wavelength determined by the refractive index of the particle, and a standing wave pattern with the apparent wavelength the same as for the incident wave. Due to the surface curvature and dielectric nature of the particle, the incident wave front undergoes a phase shift, and the resulting internal wave is focused mostly at the forward part of the particle similar to an optical lens. This focusing is also seen for irregular particles. It is concluded that, for both spherical and nonspherical particles, the interference at the far field between the partial waves that originate from these concentrated areas in the particle interior, is responsible for the specific polarization features that are common for wavelength-scale particles, such as negative values and local extrema in the degree of linear polarization, asymmetry of the phase function, and enhancement of intensity near the backscattering direction. The papers presented in this thesis solve the direct problem for particles with both simple and irregular shapes to demonstrate that these interference mechanisms are common for all dielectric wavelength-scale particles. Furthermore, it is shown that these mechanisms can be applied to both regolith particles in the optical wavelengths and hydrometeors at microwave frequencies. An advantage from this kind of study is that it does not matter whether the observation is active (e.g., polarimetric radar) or passive (e.g., optical telescope). In both cases, the internal field is computed for two mutually perpendicular incident polarizations, so that the polarization characteristics can then be analyzed according to the relation between these fields and the scattered far field.
  • Niskanen, Jukka (Helsingin yliopisto, 2013)
    Binding of a flexible polymer chain to a solid surface or air-water interface affects its conformational freedom. A polymer covalently grafted to a surface can adopt three dimensional conformations, limited however by interactions with the surface and the neighboring chains. A dense grafting of polymers forces the polymers to adopt more elongated conformations than what they would take in solutions or amorphous solid state. On the other hand, strong interactions between the polymer and the surface cause the polymer to adsorb to the surface. The air-water interface is a two dimensional space. Also in this space, polymers are more elongated than in solutions. Certain polymers that are insoluble in water can form monolayers at the air-water interface. Water soluble polymers can be anchored to the surface with hydrophobic moieties, so that the polymers do not dissolve into the bulk of the solution during the deformation of the interface. In this work, controlled radical polymerization techniques have been utilized in the syntheses of polymer grafted gold, silver and clay nanoparticles. Gold nanoparticles were grafted with the well-known thermoresponsive poly(N-isopropyl acrylamide), PNIPAM, and poly(N-isopropyl acrylamide-co-N-propyl acrylamides), P(NIPAM-NPAMs). The particles were either dispersible or non-dispersible in water. Monolayers of the polymers and polymer grafted gold nanoparticles formed on an air-water interface were characterized using a Langmuir trough. Silver nanoparticles grafted with soft acrylate copolymers, poly(butyl acrylate-co-methyl methacrylate) were produced to be used in antimicrobial coatings. A block copolymer with an oligomeric acrylic acid block located at the surface of the silver nanoparticles proved to be an optimal choice. The short hydrophilic block promoted the dissolution of silver ions from the coating and also produced the most homogenous particles. Thermoresponsive properties of poly(dimethylaminoethyl methacrylate), PDMAEMA, are strongly affected by the grafting of the polymer to montmorillonite clay nanoparticles. PDMAEMA is a weak polyelectrolyte and thus the charge of the polymer chains can easily be tuned by altering the pH of the solutions. Increasing the charge of the polymer by lowering the pH of the dispersions, or increasing the relative amount of clay in the hybrid material, had significant effects on the thermo responsive properties of PDMAEMA. Both factors change the polymer-polymer and polymer-clay interactions. Increasing the isotacticity of the thermoresponsive polymers PDMAEMA and PNIPAM affects the phase transition at the lower critical solution temperature. In fact, PNIPAM loses its water solubility when the isotacticity is high enough. The effect of increased isotacticity on the phase transition of PDMAEMA was investigated by micro calorimetry and by measuring the zeta potentials of the polymers. The interfacial properties were looked upon by conducting surface tension and interfacial surface rheological measurements on aqueous solutions of both atactic and isotactic-rich PDMAEMA. The behavior of stereoblock polymers of isotactic-atactic PNIPAM was studied at the air-water interface using interfacial surface rheology. The block sequence and thus the different architectures of the polymeric micelles had a great influence on the interfacial properties.
  • Castro, Pascal (Helsingin yliopisto, 2005)
  • Elo, Pertti (Helsingin yliopisto, 2009)
    The commodity plastics that are used in our everyday lives are based on polyolefin resins and they find wide variety of applications in several areas. Most of the production is carried out in catalyzed low pressure processes. As a consequence polymerization of ethene and α-olefins has been one of the focus areas for catalyst research both in industry and academia. Enormous amount of effort have been dedicated to fine tune the processes and to obtain better control of the polymerization and to produce tailored polymer structures The literature review of the thesis concentrates on the use of Group IV metal complexes as catalysts for polymerization of ethene and branched α-olefins. More precisely the review is focused on the use of complexes bearing [O,O] and [O,N] type ligands which have gained considerable interest. Effects of the ligand framework as well as mechanical and fluxional behaviour of the complexes are discussed. The experimental part consists mainly of development of new Group IV metal complexes bearing [O,O] and [O,N] ligands and their use as catalysts precursors in ethene polymerization. Part of the experimental work deals with usage of high-throughput techniques in tailoring properties of new polymer materials which are synthesized using Group IV complexes as catalysts. It is known that the by changing the steric and electronic properties of the ligand framework it is possible to fine tune the catalyst and to gain control over the polymerization reaction. This is why in this thesis the complex structures were designed so that the ligand frameworks could be fairly easily modified. All together 14 complexes were synthesised and used as catalysts in ethene polymerizations. It was found that the ligand framework did have an impact within the studied catalyst families. The activities of the catalysts were affected by the changes in complex structure and also effects on the produced polymers were observed: molecular weights and molecular weight distributions were depended on the used catalyst structure. Some catalysts also produced bi- or multi-modal polymers. During last decade high-throughput techniques developed in pharmaceutical industries have been adopted into polyolefin research in order to speed-up and optimize the catalyst candidates. These methods can now be regarded as established method suitable for both academia and industry alike. These high-throughput techniques were used in tailoring poly(4-methyl-1-pentene) polymers which were synthesized using Group IV metal complexes as catalysts. This work done in this thesis represents the first successful example where the high-throughput synthesis techniques are combined with high-throughput mechanical testing techniques to speed-up the discovery process for new polymer materials.