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  • Hytinantti, Timo Kalevi (Helsingin yliopisto, 2001)
  • Westerlund, Fredrik (Helsingin yliopisto, 2011)
    Relying on Merleau-Ponty's phenomenology of perception and on Mircea Eliade's works on the Sacred and the Profane, this study explores the river as a perceptual space and as the sacred Center in a cosmic vision of the world in twelve of Jean-Marie Gustave Le Clézio's fictional works, from The Interrogation (1963) to Revolutions (2003). In the first chapter, after introducing the field of study, I discuss the relation between the radical subjectivity and the evasiveness of perceiving subjects in Le Clézio's fiction. Next are some thoughts on the relation between Merleau-Ponty's and Le Clézio's ideas. The second chapter studies the river as an experience in the text, first as a topographical space, then as a sound world. The investigations move on to its water as a visual and a tactile phenomenon. Then follows the human use of the river, the (absence of) baths, and the river as a traveling space. The chapter closes with the study of the metaphorical use of the word, occurring mainly in urban space and for phenomena in the sky. The third chapter is organized around the river as the Center of the world in a religious cosmogony, where the river represents the origin of the world and of the human race. The core analysis shows how the middle of the river is a symbolic space of a new beginning. As a sacred space, the river abolishes time as the object of contemplation and as relative immobility from the point of view of a person drifting downstream. The functions of a new beginning and of abolition of time are combined in the symbolic immersions in the water. Finally, the dissertation explores other symbolical spaces, such as the unknown destination of the drift, and the river as the Center of a utopia. The chapter closes with the existential agony as a result of the elimination of the Center in the urban environment. In the final chapter, the river is compared to other watercourses : the creek, the brook and the rapids. The river is more of a spatial entity, whereas the actual water is more important in the smaller watercourses. The river is more common than the other watercourses as a topographical element in the landscape, whereas the minor watercourses invite the characters to a closer contact with their element, in immersions and in drinking their water. Finally, the work situates the rivers in a broader context of different fictional spaces in Le Clézio's text.
  • Isosävi, Johanna (Helsingin yliopisto, 2010)
    The use of forms of address in French films and their Finnish translations The use of forms of address constitutes an integral part of speakers’ communicative competence. In fact, they are not only used to assign to whom the speech is addressed, but also to construct the relationship between speakers. However, the choice of a suitable form is not necessarily evident in modern, pluralistic society. By the notion form of address, I refer to pronouns of address (tu vs. vous) and different nouns of address like names, titles (Monsieur, Madame, Mademoiselle), kinship terms, occupational terms, terms of endearment and insults. The purpose of the present thesis is, first, to study the semantic and pragmatic values of forms of address in dialogues of modern French films, and, second, their translation in Finnish subtitles. It is evident that film language is not spontaneous, but only a representation of authentic speech, and that subtitles are a written version of the original spoken language. Consequently, this thesis studies spoken fictive dialogues and their written translations. The methods applied in the study are the Interactional and Pragmatic Approach as well as Translatology. The role of forms of address in an interpersonal relationship is studied with dimensions of distance and power (Brown and Gilman 1960, Kerbrat-Orecchioni 1992), whereas the pragmatic dimension permits studying in particular the use of forms of address in speech acts (Kerbrat-Orecchioni 2001). The translation strategies are studied with the help of Venuti’s (1995) notions of foreignizing and domesticating strategies. The results of the thesis suggest that the pronoun use in the studied films is usually reciprocal. However, the relations of power have not disappeared, but are expressed in a more discrete manner with nouns of address (for instance vous + Docteur vs. vous + Anita). The use of the pronoun of address vous seems still to be common, but increased intimacy is expressed by accompanying familiar nouns of address like first names. The nominal forms of address accompany different speech acts, but not in a systematic manner. In a dialogue they appear usually in the first speech act, and more rarely in the response, but not in both. In addition, they have an important role in the mechanics of conversation. The translators here face multiple demands, and their translations seem mostly to be a compromise between foreignizing and domesticating strategies.
  • Klein, Ottilie ([according to German regulations a publication prior to the public examination is not permitted], 2015)
    The doctoral thesis investigates the cultural function of dramatic narratives of female murder. For this purpose, the study offers textual analyses of plays that feature female murder as a central event. Paying close attention to each play s plot, form, and dramaturgy, the study seeks to attach meaning to the dramatic function of women s homicidal action. The survey of women who kill in modern American drama that is at the heart of the study covers a seventy-year span (1910s - 1980s) that allows a mapping out of continuities and transitions in dramatizations of female murder. Given the politically charged nature of the figure of the female murderer, the study argues that there are two types of narratives of female murder in modern American drama (and beyond): one that uses women s homicidal action as a mechanism to create disorder at the level of plot to ultimately contain women s lethal threat by re-establishing order and thereby reinforcing dominant ideology, so-called narratives of containment; and one that exploits the ideologically disruptive potential of the female murderer to comment on social ills or to dismantle ideological contradictions, so-called lethal performances. The study concludes that the cultural function of narratives of female murder is intricately connected with the cultural and historical moment from which they emerge and the type of narrative they respond to.
  • Säde, Elina (Helsingin yliopisto, 2011)
    Leuconostoc spp. are lactic acid bacteria (LAB) implicated in food spoilage, especially on refrigerated, modified atmosphere packaged (MAP) meats. The overall aim of this thesis was to learn more about Leuconostoc spp. as food spoilage organisms with a focus on commercial products where LAB spoilage is considered a problem and the main factor limiting shelf-life. Therefore, we aimed to identify Leuconostoc spp. involved in food spoilage, as well as to characterise the spoilage reactions they caused and their contamination sources during poultry meat processing. In addition, we examined the distribution of strains of Leuconostoc gasicomitatum in different food commodities. Finally, we analysed the genome content of L. gasicomitatum LMG 18811 with a special focus on metabolic pathways related to food spoilage. The findings show that Leuconostoc gelidum and L.gasicomitatum were responsible for the discoloration and off-odours developed in beef steaks. Together with Leuconostoc mesenteroides, these Leuconostoc spp., also cause spoilage of vegetable sausages. In contrast, we showed that Leuconostoc spp. are not important for the shelf-life or quality of non-marinated broiler products although, in marinated broiler fillet products, Leuconostoc spp., L.gasicomitatum in particular, are considered spoilage organisms. Furthermore, the findings of the contamination survey we carried out in a poultry processing plant indicated that spoilage Leuconostoc spp. are derived from the processing environment rather than from the broilers, and that air movement distributes psychrotrophic spoilage LAB, including leuconostocs, and has an important role in meat contamination during poultry processing. Pulsed-field gel electrophoresis (PFGE) based genotyping of L. gasicomitatum strains demonstrated that certain genotypes are common in various meat products. In contrast, genotypes associated with meat were not recovered in vegetable-based sources. This suggests that these two food categories either become contaminated with, or favour the growth of different genotypes. Furthermore, the results indicated that the meat processing environment contributes to L. gasicomitatum contamination as certain genotypes were repeatedly identified from products of the same processing plant. Finally, the sequenced and annotated genome of L.gasicomitatum LMG 18811 allowed us to identify the metabolic pathways and reactions resulting in food spoilage.
  • Linnankivi, Tarja (Helsingin yliopisto, 2006)
    Within the last 15 years, several new leukoencephalopathies have been recognized. However, more than half of children with cerebral white matter abnormalities still have no specific diagnosis. Our aim was to classify unknown leukoencephalopathies and to identify new diseases among them. During the study, three subgroups of patients were delineated and examined further. First, we evaluated 38 patients with unknown leukoencephalopathy. Brain MRI findings were grouped into seven categories according to the predominant location of the abnormalities. The largest subgroups were myelination abnormalities (n=20) and periventricular white matter abnormalities (n=12). Six patients had uniform MRI findings with signal abnormalities in hemispheric white matter and in selective brain stem and spinal cord tracts. Magnetic resonance spectroscopy (MRS) showed elevated lactate and decreased N-acetylaspartate in the abnormal white matter. The patients presented with ataxia, tremor, distal spasticity, and signs of dorsal column dysfunction. This phenotype - leukoencephalopathy with brain stem and spinal cord involvement and elevated white matter lactate (LBSL) - was first published elsewhere in 2003. A new finding was development of a mild axonal neuropathy. The etiopathogenesis of this disease is unknown, but elevated white matter lactate in MRS suggests a mitochondrial disorder. Secondly, we studied 22 patients with 18q deletions. Clinical and MRI findings were correlated with molecularly defined size of the deletion. All patients with deletions between markers D18S469 and D18S1141 (n=18) had abnormal myelination in brain MRI, while four patients with interstitial deletions sparing that region, had normal myelination pattern. Haploinsufficiency of myelin basic protein is suggested to be responsible for this dysmyelination. Congenital aural atresia/stenosis was found in 50% of the cases and was associated with deletions between markers D18S812 (at 18q22.3) and D18S1141 (at q23). Last part of the study comprised 13 patients with leukoencephalopathy and extensive cerebral calcifications. They showed a spectrum of findings, including progressive cerebral cysts, retinal telangiectasias and angiomas, intrauterine growth retardation, skeletal and hematologic abnormalities, and severe intestinal bleeding, which overlap with features of the previously reported patients with "Coats plus" syndrome and "leukoencephalopathy with calcifications and cysts", suggesting that these disorders are related. All autopsied patients had similar neuropathologic findings showing calcifying obliterative microangiopathy. Our patients may represent an autosomally recessively inherited disorder because there were affected siblings and patients of both sexes. We have started genealogic and molecular genetic studies of this disorder.
  • Põder, Pentti (Helsingin yliopisto, 2006)
    Levosimendan is a drug developed for the treatment of heart failure. Its mechanism of action includes calcium sensitization of contractile proteins and the opening of ATP-sensitive potassium channels. The combination of positive inotropy with possible anti-ischaemic effects via potassium channel opening may offer benefits in comparison with currently available intravenous inotropes, which are contraindicated in patients with ongoing myocardial ischaemia. The active levosimendan metabolite OR-1896 significantly prolongs the duration of the haemodynamic effects of levosimendan. The aims of the present study were to investigate: 1) the clinical effects and safety of intravenous and oral levosimendan and 2) the pharmacodynamics and pharmacokinetics of intravenous and oral levosimendan and its metabolites in patients with ischaemic heart disease. Levosimendan was administered intravenously or orally in four studies to 557 patients with ischaemic heart disease with or without concomitant heart failure. One study included patients with acute myocardial infarction, while the other three studies included stable ischaemic patients. Non-invasive haemodynamic measurements were used in all studies, and blood samples for pharmacokinetics were drawn in three studies. Safety was followed by ECG recordings, adverse event inquiries and laboratory assessments. Intravenous levosimendan, administered as a 6-hour infusion did not cause clinically significant hypotension or ischaemia in comparison with placebo and reduced worsening heart failure and short- and long-term mortality. Increase in incidence of hypotension and ischaemia was seen only with the highest dose (0.4 µg/kg/min). Both intravenous and oral levosimendan possessed a moderate positive inotropic effect. Vasodilatory effect was more pronounced with intravenous levosimendan. A chronotropic effect was seen in all studies; however, it was not accompanied by any increase in arrhythmic events. The formation of levosimendan metabolites after oral dosing increased linearly with the daily dose of the parent drug, leading to increased inotropic and chronotropic response. Levosimendan was well tolerated in all studies. In conclusion, levosimendan was safe and effective in the treatment of patients with acute or chronic ischaemia. The risk-benefit ratio of intravenous levosimendan is favourable up to the dose of 0.2 µg/kg/min. The daily dose of oral levosimendan in patients with ischaemic heart failure should not exceed 4 mg due to an increase in chronotropic response.
  • Kaheinen, Petri (2009)
    Acute heart failure syndrome represents a prominent and growing health problem all around the world. Ideally, medical treatment for patients admitted to hospital because of this syndrome, in addition to alleviating the acute symptoms, should also prevent myocardial damage, modulate neurohumoral and inflammatory activation, and preserve or even improve renal function. Levosimendan is a cardiac enhancer having both inotropic and vasodilatory effects. It is approved for the short-term treatment of acutely decompensated chronic heart failure, but it has been shown to have beneficial clinical effects also in ischemic heart disease and septic shock as well as in perioperative cardiac support. In the present study, the mechanisms of action of levosimendan were studied in isolated guinea-pig heart preparations: Langendorff-perfused heart, papillary muscle and permeabilized cardiomyocytes as well as in purified phosphodiesterase isoenzyme preparations. Levosimendan was shown to be a potent inotropic agent in isolated Langendorff-perfused heart and right ventricle papillary muscle. In permeabilized cardiomyocytes, it was demonstrated to be a potent calcium sensitizer in contrast to its enantiomer, dextrosimendan. It was additionally shown to be a very selective phosphodiesterase (PDE) type-3 inhibitor, the selectivity factor for PDE3 over PDE4 being 10000 for levosimendan. Irrespective of this very selective PDE3 inhibitory property in purified enzyme preparations, the inotropic effect of levosimendan was demonstrated to be mediated mainly through calcium sensitization in the isolated heart as well as the papillary muscle preparations at clinically relevant concentrations. In the isolated Lagendorff-perfused heart, glibenclamide antagonized the levosimendan-induced increase in coronary flow (CF). Therefore, the main vasodilatory mechanism in coronary veins is believed to be the opening of the ATP-sensitive potassium (KATP) channels. In the paced hearts, CF did not increase in parallel with oxygen consumption (MVO2), thus indicating that levosimendan had a direct vasodilatory effect on coronary veins. The pharmacology of levosimendan was clearly different from that of milrinone, which induced an increase in CF in parallel with MVO2. In conclusion, levosimendan was demonstrated to increase cardiac contractility by binding to cardiac troponin C and sensitizing the myofilament contractile proteins to calcium, and further to induce coronary vasodilatation by opening KATP channels in vascular smooth muscle. In addition, the efficiency of the cardiac contraction was shown to be more advantageous when the heart was perfused with levosimendan in comparison to milrinone perfusion.
  • Sumerin, Victor (Helsingin yliopisto, 2011)
    Organocatalysis, the use of organic molecules as catalysts, is attracting increasing attention as one of the most modern and rapidly growing areas of organic chemistry, with countless research groups in both academia and the pharmaceutical industry around the world working on this subject. The literature review of this thesis mainly focuses on metal-free systems for hydrogen activation and organocatalytic reduction. Since these research topics are relatively new, the literature review also highlights the basic principles of the use of Lewis acid-Lewis base pairs, which do not react irreversibly with each other, as a trap for small molecules. The experimental section progresses from the first observation of the facile heterolytical cleavage of hydrogen gas by amines and B(C6F5)3 to highly active non-metal catalysts for both enantioselective and racemic hydrogenation of unsaturated nitrogen-containing compounds. Moreover, detailed studies of structure-reactivity relationships of these systems by X-ray, neutron diffraction, NMR methods and quantum chemical calculations were performed to gain further insight into the mechanism of hydrogen activation and hydrogenation by boron-nitrogen compounds.
  • Isei-Jaakkola, Toshiko (Helsingin yliopisto, 2004)
  • Nurmi, Susanna (Helsingin yliopisto, 2008)
    Integrins are heterodimeric transmembrane adhesion receptors composed of alpha- and beta-subunits and they are vital for the function of multicellular organisms. Integrin-mediated adhesion is a complex process involving both affinity regulation and coupling to the actin cytoskeleton. Integrins also function as bidirectional signaling devices, regulating cell adhesion and migration after inside-out signaling, but also signal into the cell to regulate growth, differentiation and apoptosis after ligand binding. The LFA-1 integrin is exclusively expressed in leukocytes and is of fundamental importance for the function of the immune system. The LFA-1 integrins have short intracellular tails, which are devoid of catalytic activity. These cytoplasmic domains are important for integrin regulation and both the alpha and beta chain become phosphorylated. The alpha chain is constitutively phosphorylated, but the beta chain becomes phosphorylated on serine and functionally important threonine residues only after cell activation. The cytoplasmic tails of LFA-1 bind to many cytoskeletal and signaling proteins regulating numerous cell functions. However, the molecular mechanisms behind these interactions have been poorly understood. Phosphorylation of the cytoplasmic tails of the LFA-1 integrin could provide a mechanism to regulate integrin-mediated cytoskeletal interactions and take part in T cell signaling. In this study, the effects of phosphorylation of LFA-1 integrin cytoplasmic tails on different cellular functions were examined. Site-specific phosphorylation of both the alpha- and beta-chains of the LFA-1 was shown to have a role in the regulation of the LFA-1 integrin.Alpha-chain Ser1140 is needed for integrin conformational changes after chemokine- or integrin ligand-induced activation or after activation induced by active Rap1, whereas beta-chain binds to 14-3-3 proteins through the phosphorylated Thr758 and mediates cytoskeletal reorganization. Thr758 phosphorylation also acts as a molecular switch to inhibit filamin binding and allows 14-3-3 protein binding to integrin cytoplasmic domain, and it was also shown to lead to T cell adhesion, Rac-1/Cdc42 activation and expression of the T cell activation marker CD69, indicating a signaling function for Thr758 phosphorylation in T cells. Thus, phosphorylation of the cytoplasmic tails of LFA-1 plays an important role in different functions of the LFA-1 integrin in T cells. It is of vital importance to study the mechanisms and components of integrin regulation since leukocyte adhesion is involved in many functions of the immune system and defects in the regulation of LFA-1 contributes to auto-immune diseases and fundamental defects in the immune system.
  • Hakulinen, Christian (Helsingin yliopisto, 2013)
    Previous studies have suggested that hostility and anger are associated with serotonergic function, that they are relatively stable personality characteristics, and that their development is affected by early family factors. Hostile and angry individuals have also been suggested to be at risk for social problems. However, there is a limited number of studies that have examined these issues from a life course perspective, which is the aim of the present thesis. The participants for the current study were from the ongoing, nationally representative, longitudinal, population-based Cardiovascular Risk in Young Finns Study (YFS), which began in 1980. The present thesis had two aims: 1) to investigate how serotonin receptor 1B, family factors, and early antecedents of hostility and anger are related to the life course development and stability of hostility and anger, and 2) how hostility over the life course is related to unemployment in adulthood. The results indicate that low parental socioeconomic status, a hostile child-rearing style and aggressive behavior in childhood predicted high levels of hostility and anger in adulthood, but the association between aggressive behavior and hostility was moderated by the serotonin receptor 1B. Both hostility and anger seemed to be moderately stable characteristics over the life course. Hostility and unemployment were found to have a bidirectional relationship, but hostility was a stronger predictor of unemployment than vice versa. The current study provides new information on unemployment as an outcome of hostility and emphasizes the role of early antecedents and family factors in the development of hostility and anger over the life course. Based on these findings, the prevention of hostility and anger should be targeted at the early stages of life. This could greatly lower the costs of high levels of hostility and anger to the individual as well as to society.
  • Paramonov, Mikhail (Helsingin yliopisto, 2015)
    The research conducted and presented herein concentrates primarily on the life cycle of a cloud condensation nucleus CCN. The primary motivation of the work is the importance of CCN in the global aerosol-cloud-climate system, and focus is placed on the production of CCN, their behaviour in the atmosphere and their properties with respect to CCN activation, as well as the removal pathways. The work presented in this thesis covers measurements performed at 16 locations around the world. The results further corroborated the notion that atmospheric new particle formation NPF is an important and widespread source of CCN in the atmosphere. The number of newly formed CCN from NPF depends on many factors, including, but not limited to, biogenic and anthropogenic emissions, frequency of NPF events, nucleation and growth rates and pre-existing CCN concentrations; method of calculation also affects the estimate of NPF contribution to CCN budgets. Highest relative increase in CCN as a result of NPF was observed at a clean remote location in Northern Finland, where in the summer the number concentration of particles above 50 nm in diameter N50 can increase by as much as 800%. Highest absolute increases in NCCN as a result of NPF (up to 3500 particles cm 3 for N50) were found at a dry savannah location of Botsalano in South Africa. In Hyytiälä Type I nucleation events were found to always, at the very least, double NCCN concentrations. It was found that in many environments around the world a rather similar fraction of aerosols activated into cloud droplets at any given level of supersaturation S, and a simple linear parameterisation is provided for an easy calculation of annual mean CCN concentration NCCN based only on total number concentration NCN and the desired S. At the majority of studied locations hygroscopicity was found to increase with size, with accumulation mode hygroscopicity parameter κ values being significantly larger than Aitken mode κ at some locations. Depending on the focus and desired accuracy, the use of κ values as a function of particle dry size rather than the assumption of a size-independent κ should preferably be considered. The photochemistry, aging processes, atmospheric NPF and other atmospheric processes occurring on a diurnal scale were found to affect the CCN activation and hygroscopic properties of Aitken mode aerosol only. The hygroscopicity of the accumulation mode aerosol is more affected by processes occurring on a time scale of a few days to months, e.g. long range transport and seasonal variation in vegetation activity. Below-cloud scavenging by snow was found to be an inefficient mechanism of CCN removal from the atmosphere compared to, e.g., in-cloud scavenging. Additionally, nucleation and Aitken mode particles are scavenged by snow more efficiently that CCN-sized aerosol. No apparent difference in the scavenging efficiency of snow was observed between a rural and an urban site in Southern Finland. Ambient relative humidity was found to correlate positively with the scavenging efficiency of snow, and a new parameterisation for calculating snow scavenging coefficients based on both particle dry size and relative humidity is presented. A reconsideration of the purpose, the focus and the motivation for the cloud condensation nuclei counter CCNC measurements at the SMEAR II is needed if they are to be continued with reasonable, interesting and exciting output.
  • Patja, Kristiina (Helsingin yliopisto, 2001)
  • Happonen, Lotta (Helsingin yliopisto, 2012)
    Viruses are the most abundant replicating entities on Earth, and they infect cells from all three domains of life - where there are cells, there are viruses. Extremophilic organisms and viruses thrive in hostile environments including hot, acidic springs, oceanic hydrothermal vents, and salt lakes. Due to their adaptation to extreme environments, these organisms and their viruses have been exploited for enzymes useful for industrial and biotechnological applications. Such enzymes include starch processing, cellulose degrading, proteolytic and DNA-processing enzymes. The latter ones are used in molecular biology applications such as polymerase chain reactions and DNA-sequencing. The aim of this study was to characterize novel, extremophilic viruses living in hot springs. I solved the three dimensional structure of two such viruses using electron cryo-microscopy and three dimensional image reconstruction, and explored the presence of extremophilic enzymes based on their genome sequence. One of the viruses characterized in this study is P23-77 that infects the thermophilic bacterium Thermus thermophilus living in alkaline hot springs. P23-77 has been proposed to belong to the Tectiviridae family of viruses characterized by an internal lipid bilayer surrounded by an icosahedral protein capsid. The structure of the icosahedral P23-77 was initially solved to 1.4 nm resolution, and subsequently to 1.0 nm resolution. The reconstruction, together with thin-layer chromatography, confirmed the presence of an internal lipid bilayer composed of neutral lipids. Analysis of the P23-77 protein profile revealed it to have 10 structural proteins, two of which were major ones based on their abundance in SDS-PAGE gels. These proteins were suggested to form the capsomers with hexameric bases of the P23-77 T = 28d capsid lattice. Surprisingly, P23-77 closely resembles the haloarchaeal virus SH1, both of which are suggested to have single β-barrel major capsid proteins, and together forming a novel viral lineage. The other virus characterized in this study is the Sulfolobus turreted icosahedral virus 2 (STIV2) infecting the crenarchaeon Sulfolobus islandicus that lives in acidic hot springs. The genome of STIV2 was sequenced, and some of its structural proteins were determined by mass-peptide fingerprinting. The structure of STIV2 was solved to 2.0 nm resolution. The genome sequence and the structure of STIV2 revealed it to resemble most closely STIV, infecting S. solfataricus. Like P23-77, both STIV and STIV2 have an outer protein capsid surrounding the internal lipid bilayer and the double-stranded (ds) DNA genome. The most striking difference between STIV and STIV2 resides in the host-cell recognition and attachments structures, which in STIV2 lacks the petal-like appendages present in STIV. Based on difference imaging, homology modeling and comparison to STIV, a model for the organization of the STIV2 virion was proposed. Furthermore, based on sequence data and homology modeling I identified the postulated genome packaging NTPase B204 of STIV2. I expressed and purified B204, and studied the nucleotide hydrolysis catalyzed by it. I furthermore solved four structures of B204 more precisely, in complex with a sulphate ion, adenosine monosphosphate, the product adenosine diphosphate, and the substrate analogue adenylylmethylenediphosphonate. B204 is the first genome packaging NTPase of a membrane-containing virus for which the structure has been solved. Based on the structure of B204, comparison to other known DNA-translocating enzymes, and other genome packaging NTPases of dsDNA and dsRNA viruses, I propose a model for the genome packaging of STIV2.
  • Torppa, Johanna (Helsingin yliopisto, 2007)
    Knowledge of the physical properties of asteroids is crucial in many branches of solar-system research. Knowledge of the spin states and shapes is needed, e.g., for accurate orbit determination and to study the history and evolution of the asteroids. In my thesis, I present new methods for using photometric lightcurves of asteroids in the determination of their spin states and shapes. The convex inversion method makes use of a general polyhedron shape model and provides us at best with an unambiguous spin solution and a convex shape solution that reproduces the main features of the original shape. Deriving information about the non-convex shape features is, in principle, also possible, but usually requires a priori information about the object. Alternatively, a distribution of non-convex solutions, describing the scale of the non-convexities, is also possible to be obtained. Due to insufficient number of absolute observations and inaccurately defined asteroid phase curves, the $c/b$-ratio, i.e., the flatness of the shape model is often somewhat ill-defined. However, especially in the case of elongated objects, the flatness seems to be quite well constrained, even in the case when only relative lightcurves are available. The results prove that it is, contrary to the earlier misbelief, possible to derive shape information from the lightcurve data if a sufficiently wide range of observing geometries is covered by the observations. Along with the more accurate shape models, also the rotational states, i.e., spin vectors and rotation periods, are defined with improved accuracy. The shape solutions obtained so far reveal a population of irregular objects whose most descriptive shape characteristics, however, can be expressed with only a few parameters. Preliminary statistical analyses for the shapes suggests that there are correlations between shape and other physical properties, such as the size, rotation period and taxonomic type of the asteroids. More shape data of, especially, the smallest and largest asteroids, as well as the fast and slow rotators is called for in order to be able to study the statistics more thoroughly.
  • Lavinto, Mikko (Helsingin yliopisto, 2015)
    The science of cosmology relies heavily on interpreting observations in the context of a theoretical model. If the model does not capture all of the relevant physical effects, the interpretation of observations is on shaky grounds. The concordance model in cosmology is based on the homogeneous and isotropic Friedmann-Robertson-Walker metric with small perturbations. One long standing question is whether the small-scale details of the matter distribution can modify the predictions of the concordance model, or whether the concordance model can describe the universe to a high precision. In this thesis, I discuss some potential ways in which inhomogeneities may change the interpretation of observations from the predictions of the concordance model. One possibility is that the small-scale structure affects the average expansion rate of the universe via a process called backreaction. In such a case the concordance model fails to describe the time-evolution of the universe accurately, leading to the mis-interpretation of observations. Another possibility is that the paths that light rays travel on are curved in such a way that they do not cross all regions with equal probability. If some regions are favoured and others disfavoured, the average description of the concordance model gives incorrect results. My collaborators and I investigated the effects of voids on the CMB using second order perturbation theory and the exact Lemaître-Tolman-Bondi solution. A void has been detected in the direction of the CMB Cold Spot, but we found that contrary to the claims made in the literature, it was not large and deep enough to explain the Cold Spot. The results from perturbation theory and exact calculation agreed to a high precision, which was not surprising, as the void is fairly shallow. We have studied a toy model of the universe, called the Swiss Cheese model, to see if the model can produce observational signals that deviate significantly from the predictions of the concordance model. We studied the backreaction in such models, and concluded that in physically motivated Swiss Cheese models, its impact on the expansion rate must be small. We also considered an unphysical model that was constructed to have the holes expand independently from the background. Even though the inhomogeneities change the expansion rate completely, the backreaction contribution to the total average expansion rate today was only at 1% level. We also studied weak lensing in a more realistic Swiss Cheese model to see how the structures change the brightness and shape of sources. We found that the simplest assumption, no change in the average flux, seemed to be violated with a probability of 98.6%. Our results agree on the magnitude of the effect, in that it should be very small, but the exact value is significantly different. There are many reasons why this may be the case, and one of the reasons is that the structures alter the area of the constant-redshift surface around the observer. However, to find conclusive proof of this, the calculation should be re-done with a higher resolution.
  • Nousiainen, Timo (Helsingin yliopisto, 2002)
  • Penttilä, Antti (Helsingin yliopisto, 2011)
    Light scattering, or scattering and absorption of electromagnetic waves, is an important tool in all remote-sensing observations. In astronomy, the light scattered or absorbed by a distant object can be the only source of information. In Solar-system studies, the light-scattering methods are employed when interpreting observations of atmosphereless bodies such as asteroids, atmospheres of planets, and cometary or interplanetary dust. Our Earth is constantly monitored from artificial satellites at different wavelengths. With remote sensing of Earth the light-scattering methods are not the only source of information: there is always the possibility to make in situ measurements. The satellite-based remote sensing is, however, superior in the sense of speed and coverage if only the scattered signal can be reliably interpreted. The optical properties of many industrial products play a key role in their quality. Especially for products such as paint and paper, the ability to obscure the background and to reflect light is of utmost importance. High-grade papers are evaluated based on their brightness, opacity, color, and gloss. In product development, there is a need for computer-based simulation methods that could predict the optical properties and, therefore, could be used in optimizing the quality while reducing the material costs. With paper, for instance, pilot experiments with an actual paper machine can be very time- and resource-consuming. The light-scattering methods presented in this thesis solve rigorously the interaction of light and material with wavelength-scale structures. These methods are computationally demanding, thus the speed and accuracy of the methods play a key role. Different implementations of the discrete-dipole approximation are compared in the thesis and the results provide practical guidelines in choosing a suitable code. In addition, a novel method is presented for the numerical computations of orientation-averaged light-scattering properties of a particle, and the method is compared against existing techniques. Simulation of light scattering for various targets and the possible problems arising from the finite size of the model target are discussed in the thesis. Scattering by single particles and small clusters is considered, as well as scattering in particulate media, and scattering in continuous media with porosity or surface roughness. Various techniques for modeling the scattering media are presented and the results are applied to optimizing the structure of paper. However, the same methods can be applied in light-scattering studies of Solar-system regoliths or cometary dust, or in any remote-sensing problem involving light scattering in random media with wavelength-scale structures.