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  • Torkkeli, Mika (Helsingin yliopisto, 2000)
  • Meriniemi, Tuukka (Helsingin yliopisto, 2014)
    The observations strongly support that the early Universe underwent an epoch of accelerated expansion called inflation. Inflation can explain many observed features of the Universe. For example it gives rise to the primordial seed required for the structure formation. Here we assume that inflation was caused by a slowly rolling scalar field called the inflaton. After the end of inflation the energy of the inflaton condensate converts into other degrees of freedom during the reheating process. A non-perturbative early stage of reheating is called preheating. In addition to the inflaton field there exists at least one other scalar field - the Standard Model Higgs field. In this thesis we study the generation of the Higgs condensate during inflation and its decay after inflation during preheating. By using the stochastic approach one can find the probable value of the Higgs field during inflation in a random Hubble patch of the Universe. One then finds that after inflation the Higgs field decays into the weak gauge bosons in a few hundreds of Hubble times. We discuss the possible observational consequences of the Higgs condensate dynamics in the early Universe. The decay of the inflaton field after the end of inflation during the preheating stage can produce a significant gravitational wave background. Here the focus is especially on the background produced by fermionic preheating. When the inflaton decays into fermions during preheating, the generated fermions develop a non-zero anisotropic stress, which serves as the source of gravitational waves. In addition the non-perturbative fermionic decay of a subdominant scalar field produces a gravitational wave background. The spectrum of the produced gravitational waves is typically peaked at very high frequencies and is unlikely to be detected by the planned gravitational wave observatories.
  • Antola, Matti (Helsingin yliopisto, 2012)
    This thesis begins by presenting the general features of technicolor models from a model building perspective. Next, a bosonic technicolor model, based on the Next-to-Minimal Walking Technicolor theory, is reviewed. In this type of model, fermion masses arise from scalar exchange with the techniquark condensate. The model passes flavor changing neutral current limits, direct search limits, and oblique constraints, in the parameter region where the fundamental scalar is heavy compared to the composite one. However, its mass is unnaturally small compared to the Planck scale. Supersymmetry can be used to naturalize fundamental scalars. After discussing general features of supersymmetric models, a supersymmetric bosonic technicolor model, based on the Minimal Walking Technicolor model, is introduced. This model has a special property: in the absence of coupling with the MSSM, the supersymmetric technicolor sector has an approximate N=4 supersymmetry. We find that this flavor extension drastically changes the condensate and low-energy spectrum compared to the naive Minimal Walking Technicolor effective theory. The model passes flavor changing neutral current limits, and oblique constraints, but in most of the otherwise viable parameter points, the Higgs particle is heavy. Finally, the N=4 extended MSSM model is presented.
  • Suhonen, Heikki (Helsingin yliopisto, 2008)
    Differentiation of various types of soft tissues is of high importance in medical imaging, because changes in soft tissue structure are often associated with pathologies, such as cancer. However, the densities of different soft tissues may be very similar, making it difficult to distinguish them in absorption images. This is especially true when the consideration of patient dose limits the available signal-to-noise ratio. Refraction is more sensitive than absorption to changes in the density, and small angle x-ray scattering on the other hand contains information about the macromolecular structure of the tissues. Both of these can be used as potential sources of contrast when soft tissues are imaged, but little is known about the visibility of the signals in realistic imaging situations. In this work the visibility of small-angle scattering and refraction in the context of medical imaging has been studied using computational methods. The work focuses on the study of analyzer based imaging, where the information about the sample is recorded in the rocking curve of the analyzer crystal. Computational phantoms based on simple geometrical shapes with differing material properties are used. The objects have realistic dimensions and attenuation properties that could be encountered in real imaging situations. The scattering properties mimic various features of measured small-angle scattering curves. Ray-tracing methods are used to calculate the refraction and attenuation of the beam, and a scattering halo is accumulated, including the effect of multiple scattering. The changes in the shape of the rocking curve are analyzed with different methods, including diffraction enhanced imaging (DEI), extended DEI (E-DEI) and multiple image radiography (MIR). A wide angle DEI, called W-DEI, is introduced and its performance is compared with that of the established methods. The results indicate that the differences in scattered intensities from healthy and malignant breast tissues are distinguishable to some extent with reasonable dose. Especially the fraction of total scattering has large enough differences that it can serve as a useful source of contrast. The peaks related to the macromolecular structure come to angles that are rather large, and have intensities that are only a small fraction of the total scattered intensity. It is found that such peaks seem to have only limited usefulness in medical imaging. It is also found that W-DEI performs rather well when most of the intensity remains in the direct beam, indicating that dark field imaging methods may produce the best results when scattering is weak. Altogether, it is found that the analysis of scattered intensity is a viable option even in medical imaging where the patient dose is the limiting factor.
  • Räisänen, Minna (Helsingin yliopisto, 2007)
    Schiff bases and their transition metal complexes are of significant current interest even though they have been prepared for decades. They have been used in various applications such as catalysis, corrosion protection, and molecular sensors. In this study, N-aryl Schiff base ketimine ligands as well as numerous new, differently substituted salen and salophen-type ligands and their cobalt(II), copper(II), iron(II), manganese(II), and nickel(II) complexes were synthesised. New solid state structures of the above compounds and the dioxygen coordination properties of cobalt(II) complexes and catalytic properties of three synthesised binuclear complexes were examined. The prepared complexes were applied in the formation of self-assembled layers on a polycrystalline gold surface and liquid-graphite interface. The effect of metal ion and ligand structure on the as-formed patterns was studied. When studying gold surfaces, a unique thiol-assisted dissolution of elemental gold was observed and a new thin gold foil preparation method was introduced. In the summary, synthesis, structures, and properties of Schiff base ligands and their transition metal complexes are described in detail and the applications of these reviewed. Assemblies of other complexes on a liquid-graphite interface and on a gold surface are also presented, and the surface characterisation methods and surfaces employed are described.
  • Johansson, Milla (Helsingin yliopisto, 2014)
    Changes in sea level behaviour on the Finnish coast of the Baltic Sea were studied, based on observations from the early 20th century to the present. The relationship of sea level changes to changes in atmospheric factors geostrophic wind and air pressure was also studied. Wind and air pressure are the main factors affecting the short-term behaviour of sea level in the Baltic Sea. Monthly mean sea levels on the Finnish coast correlate with the monthly mean zonal geostrophic wind over the Baltic Sea. The correlation explains 82 88% of the inter-annual sea level variability, and 76 81% of the intra-annual month-to-month variability. The supposed mechanism behind this involves changes in the total water volume of the Baltic Sea due to water transport through the Danish Straits, as well as the internal redistribution of water volume in the Baltic Sea basin; both processes are controlled by atmospheric factors. The seasonal sea level behaviour on the Finnish coast has changed during recent decades. In 1970 1989 sea levels were higher than previously in November December, while in 1990 2009 sea levels were higher than previously in January March. The observed annual sea level maxima have increased by 15 30 cm from the 1930s to the present. The probabilities of other higher sea levels, those exceeded a few weeks/year or less, have also increased. The increase is most evident in wintertime (January March). Part of the observed changes is related to changes in monthly mean atmospheric conditions. Mean sea levels on the Finnish coast had a declining net (apparent) trend of 1.0 7.2 mm/yr during the 20th century, mainly due to postglacial land uplift, which was partly balanced by the external large-scale sea level rise, and by an increase in the zonal wind. The large-scale sea level rise due to ocean density and circulation changes, as well as to the melting of land-based ice sheets, glaciers and ice caps, had a global average rate of 1.7 mm/yr, but the local contribution is at present uncertain. The zonal wind contributed an increasing trend of 0.5 1.2 mm/yr in sea levels on the Finnish coast. Since the 1980s, the mean sea level trends have accelerated, i.e. the decline has slowed. In the 1980s 1990s, this was due to changes in regional wind conditions. Since the 1990s, the trends still show an acceleration that is not related to regional wind conditions. A synthesis of published global sea level scenarios, and geostrophic wind scenarios from nine global circulation models, were utilized to estimate future sea level changes. On average, the changes in wind conditions will result in 6 7 cm higher sea levels on the Finnish coast by the end of this century compared to those in the present climate. The large-scale sea level rise would alone contribute 24 126 cm of sea level rise on the Finnish coast over the period 2000 2100. These changes were combined with a 41 99 cm decline due to land uplift. The accelerated sea level rise is expected to be stronger than land uplift in the Gulf of Finland, where rising relative sea levels will result. In the Gulf of Bothnia, the stronger land uplift will still balance the sea level rise, according to the average scenario. The uncertainties are large, and high-end scenarios project rising sea levels everywhere on the Finnish coast.
  • Kortelainen, Matti (Helsingin yliopisto, 2012)
    In the standard model of particle physics (SM) the masses of the elementary particles are generated by the Higgs mechanism predicting the existence of the Higgs boson. Recently the CMS and ATLAS experiments at the CERN LHC reported evidence of a new particle compatible with the SM Higgs boson. The Higgs sector of the SM suffers, however, from the so-called hierarchy problem, for which one possible solution is supersymmetry. Supersymmetric models that extend the SM to contain at least two Higgs doublets, like the minimal supersymmetric standard model (MSSM), predict the existence of a charged Higgs boson. Therefore the search for the charged Higgs boson has an important role for further studies of the Higgs sector of the fundamental theory of the elementary particles. This thesis describes a search for a light (m(H+) < m(t)) charged Higgs boson, which can be produced in the decay of the top quark, in the CMS experiment. The study considers the fully hadronic final state of top quark pair decay ttbar -> H+W-bbar, where the charged Higgs boson decays as H+ -> tau nu, tau -> hadrons+nu, with the branching fraction B(H+ -> tau nu)=~1, and the associated W boson decays to hadrons. This process is one of the most important ones for the discovery of the light charged Higgs boson. The analysis is also sensitive to the top quark pair decay ttbar -> H+H-bbar. A feature of the fully hadronic final state is that it allows the reconstruction of the transverse mass of the tau-neutrino system. The challenge is, however, the identification of the hadronic tau decays amongst the copious production of hadronic jets in QCD multijet events at the LHC. Results from the first 2.3/fb of the proton-proton collisions at the centre-of-mass energy of 7 TeV recorded by the CMS detector during the 2011 data gathering are presented. The analysed events were triggered requiring a hadronically decaying tau and missing transverse energy. At offline, the events had to have in addition at least three jets, of which at least one was identified as originating from a bottom quark. The main backgrounds were measured from data. The existence of a possible signal was statistically investigated with a frequentist method employing the distribution of the transverse mass of the tau-neutrino system. The results were combined with the other final states analysed in CMS. No significant evidence of signal was observed, and an upper limit of 2-3 % was established on the branching fraction B(t -> H+b) at the 95 % confidence level for charged Higgs boson masses between 80 and 160 GeV/c^2, with the assumption that B(H+ -> tau nu)=1. The upper limit was interpreted in the MSSM m(h)max scenario, excluding a significant region of the (tan(beta), m(H+) parameter space.
  • Kalliopuska, Juha (Helsingin yliopisto, 2007)
    By detecting leading protons produced in the Central Exclusive Diffractive process, p+p → p+X+p, one can measure the missing mass, and scan for possible new particle states such as the Higgs boson. This process augments - in a model independent way - the standard methods for new particle searches at the Large Hadron Collider (LHC) and will allow detailed analyses of the produced central system, such as the spin-parity properties of the Higgs boson. The exclusive central diffractive process makes possible precision studies of gluons at the LHC and complements the physics scenarios foreseen at the next e+e− linear collider. This thesis first presents the conclusions of the first systematic analysis of the expected precision measurement of the leading proton momentum and the accuracy of the reconstructed missing mass. In this initial analysis, the scattered protons are tracked along the LHC beam line and the uncertainties expected in beam transport and detection of the scattered leading protons are accounted for. The main focus of the thesis is in developing the necessary radiation hard precision detector technology for coping with the extremely demanding experimental environment of the LHC. This will be achieved by using a 3D silicon detector design, which in addition to the radiation hardness of up to 5×10^15 neutrons/cm2, offers properties such as a high signal-to- noise ratio, fast signal response to radiation and sensitivity close to the very edge of the detector. This work reports on the development of a novel semi-3D detector design that simplifies the 3D fabrication process, but conserves the necessary properties of the 3D detector design required in the LHC and in other imaging applications.
  • Devoto, Francesco (Helsingin yliopisto, 2013)
    This thesis reports the result of a search for the Standard Model Higgs boson in events containing four reconstructed jets associated with quarks. For masses below 135 GeV/c2, the Higgs boson decays to bottom-antibottom quark pairs are dominant and result primarily in two hadronic jets. An additional two jets can be produced in the hadronic decay of a W or Z boson produced in association with the Higgs boson, or from the incoming quarks that produced the Higgs boson through the vector boson fusion process. The search is performed using a sample of s = sqrt(1.96) TeV proton-antiproton collisions corresponding to an integrated luminosity of 9.45 fb−1 recorded by the CDF II detector. The data are in agreement with the background model and 95% credibility level upper limits on Higgs boson production are set as a function of the Higgs boson mass. The median expected (observed) limit for a 125 GeV/c2 Higgs boson is 11.0 (9.0) times the predicted standard model rate.
  • Varjonen, Samu (Helsingin yliopisto, 2012)
    In the current Internet the Internet Protocol address is burdened with two roles. It serves as the identifier and the locator for the host. As the host moves its identity changes with its locator. The research community thinks that the Future Internet will include identifier-locator split in some form. Identifier-locator split is seen as the solution to multiple problems. However, identifier-locator split introduces multiple new problems to the Internet. In this dissertation we concentrate on: the feasibility of using identifier-locator split with legacy applications, securing the resolution steps, using the persistent identity for access control, improving mobility in environments using multiple address families and so improving the disruption tolerance for connectivity. The proposed methods achieve theoretical and practical improvements over the earlier state of the art. To raise the overall awareness, our results have been published in interdisciplinary forums.
  • Hyttinen, Outi (Helsingin yliopisto, 2012)
    In this study, different types of sediments deposited in the Baltic Sea Basin in Southern Finland and the Gulf of Finland before and after the Baltic Ice Lake (BIL) drainage were examined. The aim was to gain a better understanding of changes in sedimentation in offshore, shallow water and onshore beach environments, to provide an independent age control for the drainage event, and to test the applicability of dendrochronological cross-correlation methods to varve clay data. The study consisted of acoustic sounding data from offshore, one offshore marine sediment core, six outcrops related to the BIL/Yoldia Sea transition sediments, and a digitized version of original varve measurements by Sauramo. In the Baltic basin area, the drainage of the BIL occurred close to end of the Younger Dryas cold event. This sudden 25 28 m fall in water level had originally been chosen as the zero datum for the Finnish varve clay chronology, but the "key horizon" concept was not developed further and its chronostratigraphical connection and importance remain unclear. Since the early 20th century annually laminated, or varved, sediments have been used succesfully in constructing Late Pleistocene - Holocene ice retreat chronologies and in dating ice marginal formations. This also applies to Finland. Correlating varve chronologies across the Salpausselkä zone is difficult, due to slow ice retreat rates and ice front oscillations during the Younger Dryas period. Therefore, the older part of the chronology, which pre-dates the drainage event, is only loosely connected to Holocene varve series. In offshore environment (water depth > 40 m), the falling water level triggered debris flows, which eroded and redeposited older, varved sediments creating a distinct deformation unit. In the northern Baltic proper and Gulf of Finland, up to 4 m thick, discontinuous deposits of homogeneous clay bearing traces of rotational slump and deformation were deposited. In Jokela, where the original zero varve was first described by Sauramo (1923), a homogeneous clay unit containing deformed sandy pods and layers was observed. This unit corresponds to a zero varve which was formed as a consequence of a sudden water level drop in the BIL. In shallow water environment (water depth PIENEMPI 40 m), deposition of varved sediments ceased and, as a result of rapid regression, shore processes started to operate, during which progressive marine terraces were formed. The first signs of saline incursion into southern Finnish area were ca 100 varve years after the BIL drainage. On newly emerged land, exposed sediments were prone to wind erosion. The occurrence of massive cover sands, "Lammi loess", in the Second Salpausselkä area has traditionally been attributed to rapid dust-storm type of deposition. However, there are also indications of non-aeolian origin of these deposits. Morphologically well-defined coastal terraces are related to the oldest Yoldia Sea level (YI), which was developed after the BIL drainage. One of these terraces within the First Salpausselkä zone was dated by optically stimulated luminescence (OSL) method. This is the first direct YI-level date in Finland and it yielded ages of 11 200 11 400 ± 2 700 years. The finding highlights the potential of shore terraces in verifying Lateglacial early Holocene varve chronology in Finland. Another approach to strengthen the deglaciation chronology could be applying to clay varve data the statistical methods used in dendrochronology.This approach separates the local variation within sedimentary basin from the climatic signal, and enables varve correlations over longer distances. The main findings can be summarized as following: -The BIL drainage was a basin-wide sedimentological event, leading to the deposition of a distinct drainage varve facies expressed in the annually laminated glaciolacustrine sediment as a debris-flow unit and in the shallow water sediment as the change into non-annual deposition rhythm. -After the BIL drainage, freshwater conditions prevailed in the early Yoldia sea phase for at least ca 100 200 years. -The first OSL-dating of oldest Yoldia Sea terrace (YI) in Finland gave ages of 11 200 and 11 400 ± 2 700 years. This gives also a minimum age to the BIL drainage. -Although drainage facies makes a good stratigraphic marker horizon, the erosion and redeposition related to drainage event combined with a possible hiatus in sedimentation make drainage varve facies problematic as a chronostratigraphic clay varve key horizon.
  • Soosalu, Heidi (Helsingin yliopisto, 2004)
  • Heinonen, Suvi (Helsingin yliopisto, 2013)
    Depletion of the near surface mineral deposits has created a need to develop new, innovative deep exploration tools. Seismic reflection soundings have been successfully used for hydrocarbon exploration over a century, but method s applications in the hardrock environment have been limited until recently. Strongly 3-dimensional and discontinuous geological structures are typical for the crystalline bedrock and especially for mining camps. This causes challenges to the seismic data acquisition and processing as well as to the interpretation. In this thesis, seismic reflection profiling is applied to the exploration of massive sulfide deposits in the Pyhäsalmi, Vihanti and Outokumpu area. Study areas belong to the Raahe-Ladoga belt containing 90% of the known sulfide deposits of Finland. In each of the study sites a network of seismic reflection profiles was acquired during the HIRE (HIgh REsolution reflection seismics for ore exploration 2007-2010) project by the Geological Survey of Finland. The multiphase deformation history of the study areas is demonstrated by folding, faulting and shearing that cause the complex subsurface reflectivity patters observed in the seismic data. These data enable thorough discussion on the applicability of the reflection seismic profiling for massive sulfide exploration in a geological environment that is highly deformed and metamorphosed. Careful static corrections and velocity analysis are the most important steps in the processing of the seismic reflection data acquired in hardrock terrains. Steeply dipping structures are not uncommon in the study sites and proper stacking of these structures require use of unrealistically high NMO velocities. Steep and horizontal features are best interpreted from separate stacks using 3D-visualization and modeling software. Results of velocity analysis can also be utilized in the seismic interpretation. For example in Vihanti low NMO velocities correlated with the known wide fracture zone. Difference in the acoustic impedance of the rocks defines the strength of a reflection originating from the rock contact. Geophysical drill hole logging shows that in addition to the massive sulfides, the hosting rock sequences are also strongly reflective in Vihanti, Pyhäsalmi and Outokumpu. Reflecting hosting lithology enables the determination of favorable exploration environments. In Pyhäsalmi, the known massive sulfide deposit could not be reliably identified from the seismic section because of the crooked acquisition lines, noise caused by the functioning mine and lithologically heterogeneous and strongly 3-dimensional geological background of the deposit. Based on the drill hole logging data, most reflections originate from contacts between mafic volcanic and other rocks in the Pyhäsalmi area. Mineralizations typically occur at the transition from the felsic to mafic volcanism. Reflectivity in the Pyhäsalmi area indicates continuation of the ore-critical bimodal volcanic sequence underneath wide, but shallow, granite intrusions, which has not been explored previously. Moreover, amplitude enhancement of this interpreted contact was proved to be caused by the uneconomic zinc mineralization. Amplitude enhancement inside of the reflective units interpreted as ore hosting lithology was also used as an exploration criteria in the Outokumpu area. Because sulfide ores are small compared to the typical seismic wavelength, they cause diffractions instead of reflections. Diffraction analysis was used for seismic deep exploration in Outokumpu and Vihanti. Good seismic interpretation employs the structural geology of the study area. In Pyhäsalmi, only hinges of the subvertical folds were imaged while steep limbs could not be directly imaged by seismic profiling. Gentle open folding is typical for Vihanti region and was shown as undulating reflectivity in the seismic profiles. Reverse faults interpreted in all study regions are most prominent in the Vihanti area where strong reflectors are cut by faults. Knowledge of the fault locations is important for exploration because they might have acted as pathways for fluids carrying sulfide minerals during deformation. Seismic reflection data provides an insight to the deep continuation of the fault zones. Research presented in this thesis shows that seismic reflection profiling is a useful tool for deep ore exploration. The depth resolution of the method is excellent and interpretation of the crossing seismic profiles enables the 3D geological modeling of the subsurface structures and lithological contacts. Successful modeling requires the use of other available geophysical and geological data. A geological 3D-model combines the knowledge acquired by different methods making strategic planning of exploration possible, in particular by facilitating the decisions of expensive deep drill holes. Seismic reflection profiles create the framework on which the geological model is built on.
  • Hyvönen, Tellervo (Helsingin yliopisto, 2008)
    The aim of this thesis was to study the seismic tomography structure of the earth s crust together with earthquake distribution and mechanism beneath the central Fennoscandian Shield, mainly in southern and central Finland. The earthquake foci and some fault plane solutions are correlated with 3-D images of the velocity tomography. The results are discussed in relation to the stress field of the Shield and with other geophysical, e.g. geomagnetic, gravimetric, tectonic, and anisotropy studies of the Shield. The earthquake data of the Fennoscandian Shield has been extracted from the Nordic earthquake parameter data base which was founded at the time of inception of the earthquake catalogue for northern Europe. Eight earlier earthquake source mechanisms are included in a pilot study on creating a novel technique for calculating an earthquake fault plane solution. Altogether, eleven source mechanisms of shallow, weak earthquakes are related in the 3-D tomography model to trace stresses of the crust in southern and central Finland. The earthquakes in the eastern part of the Fennoscandian Shield represent low-active, intraplate seismicity. Earthquake mechanisms with NW-SE oriented horizontal compression confirm that the dominant stress field originates from the ridge-push force in the North Atlantic Ocean. Earthquakes accumulate in coastal areas, in intersections of tectonic lineaments, in main fault zones or are bordered by fault lines. The majority of Fennoscandian earthquakes concentrate on the south-western Shield in southern Norway and Sweden. Onwards, epicentres spread via the ridge of the Shield along the west-coast of the Gulf of Bothnia northwards along the Tornio River - Finnmark fault system to the Barents Sea, and branch out north-eastwards via the Kuusamo region to the White Sea Kola Peninsula faults. The local seismic tomographic method was applied to find the terrane distribution within the central parts of the Shield the Svecofennian Orogen. From 300 local explosions a total of 19765 crustal Pg- and Sg-wave arrival times were inverted to create independent 3-D Vp and Vs tomographic models, from which the Vp/Vs ratio was calculated. The 3-D structure of the crust is presented as a P-wave and for the first time as an S-wave velocity model, and also as a Vp/Vs-ratio model of the SVEKALAPKO area that covers 700x800 km2 in southern and central Finland. Also, some P-wave Moho-reflection data was interpolated to image the relief of the crust-mantle boundary (i.e. Moho). In the tomography model, the seismic velocities vary smoothly. The lateral variations are larger for Vp (dVp =0.7 km/s) than for Vs (dVs =0.4 km/s). The Vp/Vs ratio varies spatially more distinctly than P- and S-wave velocities, usually from 1.70 to 1.74 in the upper crust and from 1.72 to 1.78 in the lower crust. Schist belts and their continuations at depth are associated with lower velocities and lower Vp/Vs ratios than in the granitoid areas. The tomography modelling suggests that the Svecofennian Orogen was accreted from crustal blocks ranging in size from 100x100 km2 to 200x200 km2 in cross-sectional area. The intervening sedimentary belts have ca. 0.2 km/s lower P- and S-wave velocities and ca. 0.04 lower Vp/Vs ratios. Thus, the tomographic model supports the concept that the thick Svecofennian crust was accreted from several crustal terranes, some hidden, and that the crust was later modified by intra- and underplating. In conclusion, as a novel approach the earthquake focal mechanism and focal depth distribution is discussed in relation to the 3-D tomography model. The schist belts and the transformation zones between the high- and low-velocity anomaly blocks are characterized by deeper earthquakes than the granitoid areas where shallow events dominate. Although only a few focal mechanisms were solved for southern Finland, there is a trend towards strike-slip and oblique strike-slip movements inside schist areas. The normal dip-slip type earthquakes are typical in the seismically active Kuusamo district in the NE edge of the SVEKALAPKO area, where the Archean crust is ca. 15-20 km thinner than the Proterozoic Svecofennian crust. Two near vertical dip-slip mechanism earthquakes occurred in the NE-SW junction between the Central Finland Granitoid Complex and the Vyborg rapakivi batholith, where high Vp/Vs-ratio deep-set intrusion splits the southern Finland schist belt into two parts in the tomography model.
  • Rissanen, Matti (Helsingin yliopisto, 2012)
    This thesis is based on eight experimental investigations of gas-phase radical-molecule kinetics, including 14 different radicals in their reactions with 4 small molecules (O2, Cl2, NO and NO2), relevant to atmospheric and combustion chemistry. These studies were performed with the same experimental apparatus, a pulsed ultraviolet (UV) laser photolysis coupled to an atomic resonance gas lamp photoionization mass spectrometer. The main interests in these studies were the rate and mechanistic parameters of the reactions investigated. Reactions were studied under pseudo-first-order conditions, with initial radical concentrations much less than the molecular reactant concentrations of the experiments ([Radical]0 << [Reactant]), as a function of temperature (188 to 500 K) and pressure [0.4 to 44 Torr helium (He)]. The experimental conditions were found to considerably affect the kinetics observed. In the R + NO2 and R + Cl2 reactions, pressure-independent reaction rates were observed and rate coefficients as a function of temperature were determined. All the rate coefficients displayed negative temperature dependence; in the CH2Cl + Cl2 and CH3CCl2 + Cl2 reactions, the sign of the temperature dependence reversed after a minimum in the temperature-dependent rate coefficient. The products observed gave insight into the possible reaction mechanisms. In a few cases, the observed products confirmed the assumed mechanism, whereas in a few others, they pointed to another reaction pathway, contrary to the expected one. In the R + O2 and R + NO reactions, pressure- and temperature-dependent reaction rates were observed, and hence, pressure falloff parameterizations of the determined rate coefficients were performed. In the allyl radical reactions, C3H5 + O2 and C3H5 + NO, an equilibrium mechanism was also observed at higher temperatures and the equilibrium constants were obtained as a function of temperature. This enabled the determination of the thermochemistries for these reactions. Together with the previous results, the formation enthalpies of the C3H5 O2 and C3H5 NO adducts were calculated. In addition, the reactivities of the radicals toward NO2 and Cl2 were explored in the current and selected similar radical reactions, and previously observed reactivity correlations were extended. The reactivity differences among these reactions were found to be connected to the different charge densities in the radical centers, i.e., related to the different charge distributions in these radicals.
  • Färm, Elina (Helsingin yliopisto, 2011)
    Atomic layer deposition (ALD) is a method to deposit thin films from gaseous precursors to the substrate layer-by-layer so that the film thickness can be tailored with atomic layer accuracy. Film tailoring is even further emphasized with selective-area ALD which enables the film growth to be controlled also on the substrate surface. Selective-area ALD allows the decrease of a process steps in preparing thin film devices. This can be of a great technological importance when the ALD films become into wider use in different applications. Selective-area ALD can be achieved by passivation or activation of a surface. In this work ALD growth was prevented by octadecyltrimethoxysilane, octadecyltrichlorosilane and 1-dodecanethiol SAMs, and by PMMA (polymethyl methacrylate) and PVP (poly(vinyl pyrrolidone) polymer films. SAMs were prepared from vapor phase and by microcontact printing, and polymer films were spin coated. Microcontact printing created patterned SAMs at once. The SAMs prepared from vapor phase and the polymer mask layers were patterned by UV lithography or lift-off process so that after preparation of a continuous mask layer selected areas of them were removed. On these areas the ALD film was deposited selectively. SAMs and polymer films prevented the growth in several ALD processes such as iridium, ruthenium, platinum, TiO2 and polyimide so that the ALD films did grow only on areas without SAM or polymer mask layer. PMMA and PVP films also protected the surface against Al2O3 and ZrO2 growth. Activation of the surface for ALD of ruthenium was achieved by preparing a RuOX layer by microcontact printing. At low temperatures the RuCp2-O2 process nucleated only on this oxidative activation layer but not on bare silicon.
  • Pohjalainen, Pietu (Helsingin yliopisto, 2013)
    Looking at engineering productivity is a source for improving the state of software engineering. We present two approaches to improve productivity: bottom-up modeling and self-configuring software components. Productivity, as measured in the ability to produce correctly working software features using limited resources is improved by performing less wasteful activities and by concentrating on the required activities to build sustainable software development organizations. Bottom-up modeling is a way to combine improved productivity with agile software engineering. Instead of focusing on tools and up-front planning, the models used emerge, as the requirements to the product are unveiled during a project. The idea is to build the modeling formalisms strong enough to be employed in code generation and as runtime models. This brings the benefits of model-driven engineering to agile projects, where the benefits have been rare. Self-configuring components are a development of bottom-up modeling. The notion of a source model is extended to incorporate the software entities themselves. Using computational reflection and introspection, dependent components of the software can be automatically updated to reflect changes in the dependence. This improves maintainability, thus making software changes faster. The thesis contains a number of case studies explaining the ways of applying the presented techniques. In addition to constructing the case studies, an empirical validation with test subjects is presented to show the usefulness of the techniques.
  • Makkonen, Juha (Helsingin yliopisto, 2009)
    Topic detection and tracking (TDT) is an area of information retrieval research the focus of which revolves around news events. The problems TDT deals with relate to segmenting news text into cohesive stories, detecting something new, previously unreported, tracking the development of a previously reported event, and grouping together news that discuss the same event. The performance of the traditional information retrieval techniques based on full-text similarity has remained inadequate for online production systems. It has been difficult to make the distinction between same and similar events. In this work, we explore ways of representing and comparing news documents in order to detect new events and track their development. First, however, we put forward a conceptual analysis of the notions of topic and event. The purpose is to clarify the terminology and align it with the process of news-making and the tradition of story-telling. Second, we present a framework for document similarity that is based on semantic classes, i.e., groups of words with similar meaning. We adopt people, organizations, and locations as semantic classes in addition to general terms. As each semantic class can be assigned its own similarity measure, document similarity can make use of ontologies, e.g., geographical taxonomies. The documents are compared class-wise, and the outcome is a weighted combination of class-wise similarities. Third, we incorporate temporal information into document similarity. We formalize the natural language temporal expressions occurring in the text, and use them to anchor the rest of the terms onto the time-line. Upon comparing documents for event-based similarity, we look not only at matching terms, but also how near their anchors are on the time-line. Fourth, we experiment with an adaptive variant of the semantic class similarity system. The news reflect changes in the real world, and in order to keep up, the system has to change its behavior based on the contents of the news stream. We put forward two strategies for rebuilding the topic representations and report experiment results. We run experiments with three annotated TDT corpora. The use of semantic classes increased the effectiveness of topic tracking by 10-30\% depending on the experimental setup. The gain in spotting new events remained lower, around 3-4\%. The anchoring the text to a time-line based on the temporal expressions gave a further 10\% increase the effectiveness of topic tracking. The gains in detecting new events, again, remained smaller. The adaptive systems did not improve the tracking results.