Faculty of Science


Recent Submissions

  • Bäckroos, Sami (Helsingin yliopisto, 2021)
    High pressure inside e.g. blood vessels or other biological cavities is a major risk factor for many preventable diseases. Most of the measuring methods require physical contact or other kinds of projected forces. Both variants can be unpleasant for the patient and additionally physical contact might warrant for either continuous disinfecting or single-use probes, depending on the measurement method and the target body part. We have been experimenting with handheld non-contacting pressure measuring devices based on acoustic waves. These excite mechanical waves, whose velocity varies with pressure, on the surface of a biological cavity. The tried excitation methods are nearly unnoticeable for the patient, allowing for more pleasant and waste free measurements. Using the data from the latest clinical trial, a new analysis algorithm was devised to improve the accuracy of the pressure estimates. Instead of the time-of-flight (TOF) of the main mechanical wave (MMW), the new algorithm estimates the pressure using the MMW and a previously unseen feature, improving the R^2 from 0.60 to 0.72.
  • Kauppala, Juuso (Helsingin yliopisto, 2021)
    The rapidly increasing global energy demand has led to the necessity of finding sustainable alternatives for energy production. Fusion power is seen as a promising candidate for efficient and environmentally friendly energy production. One of the main challenges in the development of fusion power plants is finding suitable materials for the plasma-facing components in the fusion reactor. The plasma-facing components must endure extreme environments with high heat fluxes and exposure to highly energetic ions and neutral particles. So far the most promising materials for the plasma-facing components are tungsten (W) and tungsten-based alloys. A promising class of materials for the plasma-facing components is high-entropy alloys. Many high-entropy alloys have been shown to exhibit high resistance to radiation and other wanted properties for many industrial and high-energy applications. In materials research, both experimental and computational methods can be used to study the materials’ properties and characteristics. Computational methods can be either quantum mechanical calculations, that produce accurate results while being computationally extremely heavy, or more efficient atomistic simulations such as classical molecular dynamics simulations. In molecular dynamics simulations, interatomic potentials are used to describe the interactions between particles and are often analytical functions that can be fitted to the properties of the material. Instead of fixed functional forms, interatomic potentials based on machine learning methods have also been developed. One such framework is the Gaussian approximation potential, which uses Gaussian process regression to estimate the energies of the simulation system. In this thesis, the current state of fusion reactor development and the research of high-entropy alloys is presented and an overview of the interatomic potentials is given. Gaussian approximation potentials for WMoTa concentrated alloys are developed using different number of sparse training points. A detailed description of the training database is given and the potentials are validated. The developed potentials are shown to give physically reasonable results in terms of certain bulk and surface properties and could be used in atomistic simulations.
  • Pakkanen, Noora (Helsingin yliopisto, 2021)
    In Finland, the final disposal of spent nuclear fuel will start in the 2020s where spent nuclear fuel will be disposed 400-450 meters deep into the crystalline bedrock. Disposal will follow Swedish KBS-3 principle where spent nuclear fuel canisters will be protected by multiple barriers, which have been planned to prevent radionuclides´ migration to the surrounding biosphere. With multiple barriers, failure of one barrier will not endanger the isolation of spent nuclear fuel. Insoluble spent nuclear fuel will be stored in ironcopper canisters and placed in vertical tunnels within bedrock. Iron-copper canisters are surrounded with bentonite buffer to protect them from groundwater and from movements of the bedrock. MX-80 bentonite has been proposed to be used as a bentonite buffer in Finnish spent nuclear fuel repository. In a case of canister failure, bentonite buffer is expected to absorb and retain radionuclides originating from the spent nuclear fuel. If salinity of Olkiluoto island´s groundwater would decrease, chemical erosion of bentonite buffer could result in a generation of small particles called colloids. Under suitable conditions, these colloids could act as potential carriers for immobile radionuclides and transport them outside of facility area to the surrounding biosphere. Object of this thesis work was to study the effect of MX-80 bentonite colloids on radionuclide migration within two granitic drill core columns (VGN and KGG) by using two different radionuclides 134Cs and 85Sr. Batch type sorption and desorption experiments were conducted to gain information of sorption mechanisms of two radionuclides as well as of sorption competition between MX-80 bentonite colloids and crushed VGN rock. Colloids were characterized with scanning electron microscopy (SEM) and particle concentrations were determined with dynamic light scattering (DLS). Allard water mixed with MX-80 bentonite powder was used to imitate groundwater conditions of low salinity and colloids. Strontium´s breakthrough from VGN drill core column was found to be successful, whereas caesium did not breakthrough from VGN nor KGG columns. Caesium´s sorption showed more irreversible nature than strontium and was thus retained strongly within both columns. With both radionuclides, presence of colloids did not seem to enhance radionuclide´s migration notably. Breakthrough from columns was affected by both radionuclide properties and colloid filtration within tubes, stagnant pools and fractures. Experiments could be further complemented by conducting batch type sorption experiments with crushed KGG and by introducing new factors to column experiments. The experimental work was carried out at the Department of Chemistry, Radiochemistry in the University of Helsinki.
  • Säde, Solja (Helsingin yliopisto, 2021)
    Photocatalytic reactions utilize energy harnessed from light for the activation of a catalyst. In photoredox catalysis, an excited photocatalyst can take part in redox reactions with a substrate. The most common photocatalysts could be divided into three classes: metal catalysts, organic dyes, and heterogeneous semiconductors. These catalysts are often employed with a transition metal dual catalyst. The dual catalyst enables the cross-coupling of substrates, and the photocatalyst oxidizes or reduces the dual catalyst. Photocatalytic reactions can offer a milder alternative for the traditional C-N coupling reactions. In the literature review section, the photocatalytic N-arylation of pyrrolidines was examined. The review found that pyrrolidines were successfully N-arylated with all of the catalyst types, and multiple variations on the substituents on the aryl halide. In the majority of the research, electron withdrawing groups (EWG) as substituents enhanced product yields, but electron donating groups (EDG) decreased yields. In an organic dye catalysed reaction, the effects of the substituents were opposite. In addition, the photocatalytic reactions were compared with traditional C-N coupling reactions, such as the Buchwald-Hartwig reaction, Ullmann-type reactions nucleophilic aromatic substitution and the Chan-Lam reaction. These reactions often had harsh reaction conditions. The photocatalytic N-arylation of 3-substituted pyrrolidines was examined in the experimental part of this thesis. The objectives of this study were to investigate the use of photoredox methodologies for the C-N coupling of 3-substituted pyrrolidines to arenes and examine the scope and limitations of the reaction and the effects of substituents. In addition, the aim was to optimize the reaction conditions for multiple parameters and for each product separately, apply the reaction on a flow chemistry appliance, and execute scale-up reactions on both photoreactors. The study found 3-substituted pyrrolidines to be successfully coupled with aryl halides with great variation in the substituents of both starting materials. With optimization, the reactions with lower product yields were able to be improved significantly. The reaction was successfully upscaled, but the adaptation on the flow reactor requires further optimization. Photocatalytic C-N coupling reactions offer a promising alternative for traditional reactions.
  • Zhu, Yangming (Helsingin yliopisto, 2021)
    C-H bonds are abundantly present in organic compounds and therefore represent large class of targets for activation in modern synthetic chemistry. Starting from simple and usually inexpensive compounds, direct activation of C-H bonds provides atom efficient (low waste generation) access to highly functionalized products with high added value. One of the most desirable subclass of C-H bond functionalization is its transformation to C-B bond (borylation), as organoboron compounds are important and widely used building blocks in organic synthesis, in particularly pharmaceuticals, agricultural chemicals and organic materials. Traditionally, transition metal-based catalysts have been used for C-H borylation. Recently, interest has grown towards metal-free approaches. This thesis is focused on the development of metal-free Csp2-H borylation of arenes by coupling two main concepts: borenium cations and Frustrated Lewis Pairs (FLPs). Borenium cations are positively charged boron species possessing two σ-bound substituents, and the third coordination site occupied by a ligand (L) bound through coordinative dative interaction. Due to relative stability ensured by donor ligand and enhanced reactivity owing to unsaturated coordinate sphere and positive charge, chemistry of boreniums attracted considerable attention. FLPs comprise separated (intermolecular) or bound within one molecule (intramolecular) Lewis acidic and Lewis basic components, which are prevented from formation of classical Lewis adduct due to steric repulsion. Since FLPs posses unquenched reactivity they are capable to cleave heterotically σ and π chemical bonds, including C-H bonds. The method showed in the present work implies cooperative actions of 2-aminopyridinyl-borenium based FLPs, comprising borenium cation as LA component, and bulky aminopyridine ligand as LB component to borylate aromatic Csp2-H bonds. In this approach, LA serves as a reagent itself (source of boron), while LB (ligand), which abstract proton upon C-H bond cleavage, can be fully recovered from the reaction mixture. Thus, this approach offers high atom efficiency and low waste generation. We achieved borylation of electron-rich thiophenes, furans, and pyrroles under ambient conditions. Further we dedicated our efforts to improve efficiency and economical aspect of the proposed method.
  • Rawlings, Alexander (Helsingin yliopisto, 2021)
    This thesis presents the results from seventeen collisionless merger simulations of massive early-type galaxies in an effort to understand the coalescence of supermassive black holes (SMBHs) in the context of the Final Parsec Problem. A review of the properties of massive early-type galaxies and their SMBHs is presented alongside a discussion on SMBH binary coalescence to motivate the initial conditions used in the simulations. The effects of varying SMBH mass and stellar density profiles in the progenitor initial conditions on SMBH coalescence was investigated. Differing mass resolutions between the stellar particles and the SMBHs for each physical realisation were also tested. The simulations were performed on the supercomputers Puhti and Mahti at CSC, the Finnish IT Centre for Science. SMBH coalescence was found to only occur in mergers involving SMBH binaries of equal mass, with the most rapid coalescence observed in galaxies with a steep density profile. In particular, the eccentricity of the SMBH binary was observed to be crucial for coalescence: all simulations that coalesced displayed an orbital eccentricity in excess of e=0.7 for the majority of the time for which the binary was bound. Simulations of higher mass resolution were found to have an increased number of stellar particles able to positively interact with the SMBH binary to remove orbital energy and angular momentum, driving the binary to coalescence. The gravitational wave emission from an equal mass SMBH binary in the final stages before merging was calculated to be within the detection limits required for measurement by pulsar timing arrays. Mergers between galaxies of unequal mass SMBHs were unable to undergo coalescence irrespective of mass resolution or progenitor density profile, despite the binary in some of these simulations displaying a high orbital eccentricity. It was determined that the stellar particles interacting with the SMBH binary were unable to remove the required orbital energy and angular momentum to bring the SMBHs to within the separation required for efficient gravitational wave emission. A trend between increasing mass resolution and increasing number of stellar particles able to remove energy from the SMBH binary was observed across all the simulation suites. This observation is of paramount importance, as three-body interactions are essential in removing orbital energy and angular momentum from the SMBH binary, thus overcoming the Final Parsec Problem. As such, it is concluded that the Final Parsec Problem is a numerical artefact arising from insufficient mass resolution between the stellar particles and the SMBHs rather than a physical phenomenon.
  • Sallasmaa, Christa (Helsingin yliopisto, 2021)
    The topic of this thesis is participatory budgeting and its connection to the discussion between neoliberalism and participatory governance in the context of city development. Helsinki started its own model of participatory budgeting in 2018 and has pledged to continue the concept in the future. I examine whether Helsinki’s participatory budgeting has the potential to support the ideologies of neoliberalism or participatory governance. In practice, I am exploring the views from the city government and active members of Helsinki’s neighborhood associations. Neighborhood associations had a significant role in the original participatory budgeting of Porto Alegre. I used interview and qualitative survey to collect my data. Neoliberalism has influenced the inequality between regions and the so-called crisis of democracy. Direct involvement of citizens is seen as a solution to these problems. Neoliberalism and participation have a paradoxical relationship: they have received similar criticism. In participatory governance participation means deliberative decision-making based on exchange of knowledge, but in neoliberalism participation can be a rhetoric tool to cover up actual decision-making or a city branding technique. Porto Alegre’s original model of participatory budgeting is seen as a part of participatory governance, but many of the international models seem to be more compatible with neoliberal ideology. The city government has not reserved enough resources to the participatory budgeting. The execution was rushed and showed signs of rationalization. According to the interview and the qualitative survey, inequality between regions might be the downfall of Helsinki’s participatory model. The active members of neighborhood associations see the benefits of participation budgeting but only from the perspective of certain regions. Currently, Helsinki’s participatory budgeting works better as a branding technique than as a method of decision-making. It seems to be more compatible with neoliberalism than participatory governance.
  • Penttinen, Jussi (Helsingin yliopisto, 2021)
    HMC is a computational method build to efficiently sample from a high dimensional distribution. Sampling from a distribution is typically a statistical problem and hence a lot of works concerning Hamiltonian Monte Carlo are written in the mathematical language of probability theory, which perhaps is not ideally suited for HMC, since HMC is at its core differential geometry. The purpose of this text is to present the differential geometric tool's needed in HMC and then methodically build the algorithm itself. Since there is a great introductory book to smooth manifolds by Lee and not wanting to completely copy Lee's work from his book, some basic knowledge of differential geometry is left for the reader. Similarly, the author being more comfortable with notions of differential geometry, and to cut down the length of this text, most theorems connected to measure and probability theory are omitted from this work. The first chapter is an introductory chapter that goes through the bare minimum of measure theory needed to motivate Hamiltonian Monte Carlo. Bulk of this text is in the second and third chapter. The second chapter presents the concepts of differential geometry needed to understand the abstract build of Hamiltonian Monte Carlo. Those familiar with differential geometry can possibly skip the second chapter, even though it might be worth while to at least flip through it to fill in on the notations used in this text. The third chapter is the core of this text. There the algorithm is methodically built using the groundwork laid in previous chapters. The most important part and the theoretical heart of the algorithm is presented here in the sections discussing the lift of the target measure. The fourth chapter provides brief practical insight to implementing HMC and also discusses quickly how HMC is currently being improved.
  • Suominen, Henri (Helsingin yliopisto, 2021)
    Online hypothesis testing occurs in many branches of science. Most notably it is of use when there are too many hypotheses to test with traditional multiple hypothesis testing or when the hypotheses are created one-by-one. When testing multiple hypotheses one-by-one, the order in which the hypotheses are tested often has great influence to the power of the procedure. In this thesis we investigate the applicability of reinforcement learning tools to solve the exploration – exploitation problem that often arises in online hypothesis testing. We show that a common reinforcement learning tool, Thompson sampling, can be used to gain a modest amount of power using a method for online hypothesis testing called alpha-investing. Finally we examine the size of this effect using both synthetic data and a practical case involving simulated data studying urban pollution. We found that, by choosing the order of tested hypothesis with Thompson sampling, the power of alpha investing is improved. The level of improvement depends on the assumptions that the experimenter is willing to make and their validity. In a practical situation the presented procedure rejected up to 6.8 percentage points more hypotheses than testing the hypotheses in a random order.
  • Riihimäki, Katariina (Helsingin yliopisto, 2021)
    Mafis-ultramafinen Kevitsan intruusio, joka sijaitsee Keski-Lapin vihreäkivivyöhykkeessä Pohjois-Suomessa, sisältää pirotteisen Ni-Cu-PGE-esiintymän. Kairareikä KVX018 lävistää intruusion ja sen pohjakontaktin, ja kairareiästä on havaittu suhteellisen matalan resistiivisyyden vyöhyke intruusion syvimmissä osissa. KVX018 on syvin Kevitsan intruusioon kairattu tutkimusreikä ja havaittu vyöhyke on ainutlaatuinen tutkimusalueella. Aiemmat tutkimukset osoittavat intruusion pohjakontaktin erottuvan seismisissä heijastusluotauksissa ja sisältävän mahdollisesti mineralisaation. Tässä työssä tutkitaan Kevitsan intruusion pohjakontaktin erityispiirteitä KVX018 kairasydämestä, ja tulkitaan matalan resistiivisyyden alkuperää ja sen yhteyttä mineralogiaan. Geokemiallisten ja petrografisten piirteiden perusteella tutkitussa kairareiän osassa (1551-1878 m) havaitaan neljä toisistaan poikkeavaa yksikköä: jalkapuoli (sivukivet), kontaktivyöhyke, alemmat kumulaatit ja ylemmät kumulaatit. Alempien kumulaattien havaittiin olevan voimakkaasti kontaminoituneita hydrotermisiin liuoksiin peruskalliosta liuenneista alkuaineista. Kontaminaatio havaittiin 125 metriä pohjakontaktista ylöspäin kohonneina litiumin, lantaanin, rubidiumin ja kaliumin pitoisuuksina, sekä näiden alkuaineiden ehtymisenä kontaktin lähellä jalkapuolen kivissä. Kontaktivyöhyke on voimakkaasti silisifikoitunut ja albiittiutunut. Hydrotermisten liuosten aktiivisuus pohjakontaktin läheisyydessä havaitaan myös plagioklaasin muuttumisena epidootiksi. Kontaktivyöhykkeessä on kapea mineralisaatio, joka tulkittiin ”false ore”-tyypin malmiksi ja sen sulfidien nikkelipitoisuudeksi laskettiin 2,28 %. Kontaktivyöhykkeestä ylöspäin mineralisaation todettiin ensin olevan heikkolaatuista Ni-PGE malmia ja sen yläpuolella ”normal ore”-tyypin malmia. Ultramafisten intrusiivisten kivien havaittiin olevan muuttuneita amfiboli-muuttumisen tuloksena paikallisesti niin voimakkaasti, että alkuperäistä mineralogiaa ja tekstuureja ei pystytty määrittämään. Muuttumisen intensiteetti voimistuu intruusion pohjaosissa syvemmälle mentäessä. Suolamineraaleja todettiin silmämääräisesti joidenkin näytteiden pinnalla ja röntgendiffraktio-menetelmällä (XRD) yhdessä näytteessä. XRD tulokset osoittivat tutkitun näytteen sisältävän nitratiinia ja sylviittia, jotka ovat evaporiiteissa tyypillisesti esiintyviä suolamineraaleja, ja joiden esiintyminen saattaa viitata evaporiittisten sedimenttien osallistuneen malminmuodostukseen. Kivien resistiivisyyteen vaikuttavat mm. kiven sulfidipitoisuus, suolapitoisuus, huokoisuus ja muuttuminen. Resistiivisyyden ja varautuvuuden havaittiin korreloivan, joka viittaa resistiivisyyden korreloivan myös sulfidimineraalien esiintymisen kanssa. Kuitenkin 680 metrin syvyyden jälkeen resistiivisyys pienenee ilman vastaavaa muutosta muissa petrofysikaalisissa ominaisuuksissa. Tämän tutkimuksen perusteella matala resistiivisyys johtuu suola- ja sulfidimineraaleista, sekä intruusion kivien voimakkaasta muuttumisesta.
  • Mesimäki, Johannes (Helsingin yliopisto, 2021)
    Collisions and near accidents between pedestrians and cyclists can result in serious injuries and death but have received limited academic attention. Using an online survey, this thesis aimed to increase knowledge of such events, assess the sense of safety of pedestrians and cyclists in traffic as well as identify safety-related constraints to the uptake of walking and cycling with practice theory. Practice theory considers human behaviour to be guided via participation in established social practices constituted by interconnected elements of meaning, material and competence. As such, this thesis contributes to debates concerning barriers to walking and cycling from a safety perspective. The survey was directed to Finnish cities with over 100,000 population and asked frequent pedestrians and cyclists to report details of collisions and near accidents between pedestrians and cyclists that they had experienced in the previous three years. Additionally, the survey asked questions concerning respondents’ sense of safety in traffic when walking or cycling. Survey data was analysed with chi-square tests of independence and ordinal logistic regression. Constraints to the uptake of cycling and walking and ways to overcome them were identified with a practice theory analysis. This involved examining the implications of survey results for the elements constituting the practices, their interrelations and how the practices influenced each other. According to the results, near accidents are roughly 50 times more frequent than collisions. Only 16 respondents had experienced a collision, whereas roughly a third had experienced at least one near accident. Additionally, shared paths were associated with more collisions and near accidents compared to separated spaces, and respondents felt less safe and less willing to travel on them compared to separated paths. The most common type of collision and near accident involved both road users travelling in the same direction. Constraints to cycling and walking were found to surface from meanings of danger associated particularly with shared infrastructure, a material element of the practices. These issues are evidenced by a high near accident frequency, low sense of safety and low willingness to travel on shared spaces. In addition, these issues were exacerbated by a lack of competences concerning space sharing, resulting in poor rapport and respect between pedestrians and cyclists. Significant effects regarding sense of safety were detected between pedestrians and cyclists and across age and genders with ordinal logistic regression, suggesting variance in how different groups experience meanings of danger. Intervening in the material element of the practices by preferring the provision of spatially separated infrastructure was considered to have potential to help overcome these constraints due to their associated safety benefits and respondents’ more favourable position toward them. In addition, working to develop a shared code of conduct for travel on shared environments could further mitigate constraints. Overcoming these constraints could assist the promotion of active travel and help improve the sustainability of transport while improving traffic safety and increasing physical activity.
  • Koivisto, Teemu (Helsingin yliopisto, 2021)
    Programming courses often receive large quantities of program code submissions to exercises which, due to their large number, are graded and students provided feedback automatically. Teachers might never review these submissions therefore losing a valuable source of insight into student programming patterns. This thesis researches how these submissions could be reviewed efficiently using a software system, and a prototype, CodeClusters, was developed as an additional contribution of this thesis. CodeClusters' design goals are to allow the exploration of the submissions and specifically finding higher-level patterns that could be used to provide feedback to students. Its main features are full-text search and n-grams similarity detection model that can be used to cluster the submissions. Design science research is applied to evaluate CodeClusters' design and to guide the next iteration of the artifact and qualitative analysis, namely thematic synthesis, to evaluate the problem context as well as the ideas of using software for reviewing and providing clustered feedback. The used study method was interviews conducted with teachers who had experience teaching programming courses. Teachers were intrigued by the ability to review submitted student code and to provide more tailored feedback to students. The system, while still a prototype, is considered worthwhile to experiment on programming courses. A tool for analyzing and exploring submissions seems important to enable teachers to better understand how students have solved the exercises. Providing additional feedback can be beneficial to students, yet the feedback should be valuable and the students incentivized to read it.
  • Lauha, Patrik (Helsingin yliopisto, 2021)
    Automatic bird sound recognition has been studied by computer scientists since late 1990s. Various techniques have been exploited, but no general method, that could even nearly match the performance of a human expert, has been developed yet. In this thesis, the subject is approached by reviewing alternative methods for cross-correlation as a similarity measure between two signals in template-based bird sound recognition models. Template-specific binary classification models are fit with different methods and their performance is compared. The contemplated methods are template averaging and procession before applying cross-correlation, use of texture features as additional predictors, and feature extraction through transfer learning with convolutional neural networks. It is shown that the classification performance of template-specific models can be improved by template refinement and utilizing neural networks’ ability to automatically extract relevant features from bird sound spectrograms.
  • Sipilä, Suvi (Helsingin yliopisto, 2020)
    Clean and high-quality code affects the maintainability of software throughout the software lifecycle. Cleanliness and high-quality should be pursued from the software development phase. Nowadays, the software is developed rapidly, which is why the code must be easy to maintain. When the code is easy to maintain, it can basically be managed by any software developer. The thesis conducted a literature review of clean and high-quality code. The thesis aimed to find out what is clean and high-quality code in the class and function level. The purpose of the thesis was to explain why clean and high-quality code is necessary and how the clean and high-quality code can be improved with different tools such as metrics, refactoring, code review, and unit tests. The thesis also included a survey for software developers. The survey sought an answer to how clean and high-quality code practices are implemented in working life from the perspective of software developers. 103 software professionals responded to the survey. Based on the responses, 82,5 \% of respondents felt that they always or usually write clean and high-quality code. The main reasons why clean and high-quality code cannot be written were the challenges of the old codebase and schedule pressures. Writing code is a very people-oriented job, so we must understand the code and its purpose. The code must be simple and carefully written. When the code is clean and high-quality, it is easier to read and understand, and thus easier to maintain.
  • Porttinen, Peter (Helsingin yliopisto, 2020)
    Computing an edit distance between strings is one of the central problems in both string processing and bioinformatics. Optimal solutions to edit distance are quadratic to the lengths of the input strings. The goal of this thesis is to study a new approach to approximate edit distance. We use a chaining algorithm presented by Mäkinen and Sahlin in "Chaining with overlaps revisited" CPM 2020 implemented verbatim. Building on the chaining algorithm, our focus is on efficiently finding a good set of anchors for the chaining algorithm. We present three approaches to computing the anchors as maximal exact matches: Bi-Directional Burrows-Wheeler Transform, Minimizers, and lastly, a hybrid implementation of the two. Using the maximal exact matches as anchors, we can efficiently compute an optimal chaining alignment for the strings. The chaining alignment further allows us to determine all such intervals where mismatches occur by looking at which sequences are not in the chain. Using these smaller intervals lets us approximate edit distance with a high degree of accuracy and a significant speed improvement. The methods described present a way to approximate edit distance in time complexity bounded by the number of maximal exact matches.
  • Lindström, Olli-Pekka (Helsingin yliopisto, 2021)
    Until recently, database management systems focused on the relational model, in which data are organized into tables with columns and rows. Relational databases are known for the widely standardized Structured Query Language (SQL), transaction processing, and strict data schema. However, with the introduction of Big Data, relational databases became too heavy for some use cases. In response, NoSQL databases were developed. The four best-known categories of NoSQL databases are key-value, document, column family, and graph databases. NoSQL databases impose fewer data consistency control measures to make processing more efficient. NoSQL databases haven’t replaced SQL databases in the industry. Many legacy applications still use SQL databases, and newer applications also often require the more strict and secure data processing of SQL databases. This is where the idea of SQL and NoSQL integration comes in. There are two mainstream approaches to combine the benefits of SQL and NoSQL databases:multi-model databases and polyglot persistence. Multi-model databases are database management systems that store and process data in multiple different data models under the same engine. Polyglot persistence refers to the principle of building a system architecture that uses different kinds of database engines to store data. Systems implementing the polyglot persistence principle are called polystores. This thesis introduces SQL and NoSQL databases and their two main integration strategies: multi-model databases and polyglot persistence. Some representative multi-model databases and polystores are introduced. In conclusion, some challenges and future research directions for multi-model databases and polyglot persistence are introduced and discussed.
  • Ilonen, Annukka (Helsingin yliopisto, )
    In the 21st century, there is an intensified social-political mindset, where people are no longer separated from nature. As a result concepts and theories of ecological research become part of regional policy and spatial planning. At the same time, ecological knowledge, technology orientation and the economic potential created by them form an equilibrium between them. It may, depending on the context, turn to the barrier or benefit of the economy. Talking about the ecologicalization of politics which affecting all spatial planning levels in Finland. It has caused to conflicts in land use planning, when you try to take into account the importance of the nature of knowledge and to protect the directive species, such as flying squirrels. The aim of the study is to find out about the written material and the interviews with the peasants: what the flying squirrel conservation is all about and how it related to the ecologicalization of politics and what are the reasons for the species's conservation zoning conflicts and how can they be solved? As a case study, I will look at the Tramway project in Tampere, from the point of view of the flying squirrel’s conflict and ecologicalization of politics. At the same time, the aim is to develop the concept of ecologicalization of politics and to produce new information about the prevailing greenish social change. Flying squirrel (Pteromys volans) is protect by a politically determined decision in the European Union area and it’s the small-scale night-life mammal which occurs grown up in mixed forests. In the EU, species occur in Finland and small quantities in Estonia and possibly in Latvia. Given that the EU is responding to the problem of state protection, the common species in Finland is the directive specie which requires special protection. The Habitats Directive has been implemented in Finland's National Nature Conservation Act at the end of the 1990s and the directive prohibits the eradication and deterioration of breeding and resting places of the species. In addition, the guiding regulation of the protection of the flying squirrel is included in the Land Use and Building Act, Land Act and Forest Law. Despite the protection of the flying squirrel population is estimated declined from the period after the Second World War in Finland, but the species is classified as held for an eye only. The calculation of population classification has been criticized. The entry into force of the Land Use and Building Act in 2000 was an important legal reform for the protection of the flying squirrel. A key change in the law had made land use planning objectives addition of "conservation of biodiversity and other natural values". In addition, the sections on increasing interaction and impact assessment of zoning have made the planning process more transparent and added the importance of nature enthusiasts. Influencing people often involves complaining about patterns, which is unfortunate. It offers residents the opportunity to influence the surrounding environment and protect nature, such as flying squirrels. Grown up in mixed forests of the flying squirrel favored often set in the cities, because the mixed forests have reduced and fragmented due to forestry in outside the cities. Urban forests directed to a plurality of user requirements, because it can be flying squirrel homeforests, residents recreational use, commercial forest and zoning residences area. Flying squirrel in the comfort of urban forests is challenging because growing cities expand and condense. The protection of the flying squirrel has caused conflict’s situations in many cities. An example of this is Pirkanmaa long flying squirrel conflict history and its recent case in Tampere’s tram project. The tramway is a matter of valuing of the political decision-making, where the construction the tram means ignoring another environmental value, nature conservation. The flexible nature of ecologicalization of politics is manifested in a tramway project, when ecological knowledge of the flying squirrel turns against economic goals and co-operation between actors. For people who benefit from economic growth and for the city's growth, the flying squirrel is a financial slowdown which complicates regional cooperation in Tampere urban area. Although the protection of flying squirrel is not just a matter of protecting the city's local level, but also regional co-operation, as the dynamic species moves away from the municipal boundaries.
  • Kämäri, Hannu (Helsingfors universitet, 2017)
    Tässä pro gradu -tutkielmassa tavoitteena oli luoda referenssiarkkitehtuuri Big Data -teknologioita hyödyntäen sensoridatan vastaanottamiseksi ja käsittelemiseksi. Luotavan referenssiarkkitehtuurin oli tarkoitus laajentaa olemassa olevaa tietoarkkitehtuuria sensoriaineiston käsittelyn vaatimilla komponenteilla. Nykyinen tietoarkkitehtuuri koostuu operatiivisesta tietokannasta ja tietovarastosta, johon tiedot historioidaan raportoinin tarpeisiin. Toiminnallisena taustana muutokselle on ympäristöterveydenhuollon järjestelmäuudistus. Uuden järjestelmän yhdeksi tavoitteeksi on asetettu sensoridatan käytön lisääminen. Elintarviketurvallisuuden osalta ilmeisin vaihtoehto on Eviran asiantuntijoiden mukaan ravintoloiden kylmätilojen lämpötilan ja kosteuden mittaaminen. Sensoriaineistoa arvioitiin tulevan niin paljon, että sen käsittely ei tietoarkkitehtuurin nykyisillä ratkaisulla olisi mahdollista. Tapauksen pohjalta luotiin vaatimusluettelo ja sen tueksi kerätiin olennaiset kohdat nykyisen järjestelmätoimittajan arkkitehtuuriperiaatteista. Ratkaisua haluttiin etsiä Big Data -teknologioista ja erityisesti reaaliaikaiseen tiedonkäsittelyn mahdollistavista tietovirtojen käsittelyyn suunnatuista teknologioista. Työ on luonteeltaan konstruktiivinen. Siinä luotiin referenssiarkkitehtuuri, joka arvioitiin DCAR-mentelmällä. Arkkitehtuurin rakentamista taustoitettiin teknologiakartoituksella tietovirtojen käsittelyyn tarkoitetuista Big Data -teknologioista. Referenssiarkkitehtuuri kuvatiin JHS-179 -standardilla. Toteutettu kokonaisuus sisältää kuvaukset toiminta, tieto-, tietojärjestelmä ja teknologia-arkkitehtuureista.
  • Kapoor, Shubham (Helsingfors universitet, 2017)
    Challenges in managing cellular networks have grown in magnitude over the years. Upcoming 5G networks will further complicate the problem by introducing a larger number of scattered Network Elements (NEs) and functions than the prior cellular generations. Due to investment costs and user retention reasons, older technologies are not completely scraped out while new technologies are being introduced in the network. This results in a large, heterogeneous and complex network, which makes the data used to manage the network i.e. Management Plane (M-Plane) data, a big data candidate for the telcos. The conventional centralised Network Management Systems (NMS) will face fundamental scaling challenges in processing this big data, be it its collection, storage or quick analysis. In this thesis, we propose a novel concept of Quality of Monitoring (QoM) classes, which could be used for mobile edge compression of M-plane data. QoM classes specify the quality by which M- Plane data can be collected from the NEs. Quality here specifies the amount of relative information loss acceptable by network management applications consuming M-Plane data. The best QoM class with zero information loss could be assigned to monitor most critical NEs, while inferior QoM classes with some degree of information loss could be assigned to monitor auxiliary NEs. The proposed solution is based on the Publish/Subscribe paradigm for data delivery. The Publish/Subscribe paradigm makes the solution scalable and efficient by collecting data only once and providing flexibility to update QoM class subscription on the fly. The solution aggregates raw M-Plane data into a smaller set of the operator-defined performance metrics. This data is further compressed by removing portions of data with redundant or small information content. This helps the proposed solution to achieve reduction in the complexities of 3Vs (Volume, Variety and Velocity) of M-Plane data. The solution achieves quick processing of M-Plane data while saving the computational, bandwidth, storage and energy resources of the cellular operator.
  • Louhiranta, Juha (Helsingin yliopisto, 2020)
    Tämä pro gradu -tutkielma tarkastelee vaatimusmäärittelyä ketteriä menetelmiä hyödyntävissä ohjelmistoprojekteissa. Tavoitteena on selvittää, miten ohjelmiston vaatimukset muodostuvat ketterien menetelmien avulla ja millaisia vaikutuksia niillä on vaatimusmäärittelyprosessiin. Lisäksi tutkielmassa tarkastellaan, millaisia hyötyjä ketterillä menetelmillä voidaan saavuttaa vaatimusmäärittelyssä ja minkälaisia ongelmia ne saattavat aiheuttaa ohjelmistoprojektin eri vaiheissa. Tutkielmassa myös etsitään eroja ketterien menetelmien ja ketterän vaatimusmäärittelyprosessin sekä perinteisten menetelmien välillä. Tutkielman tapaustutkimuksen kohteena on Helsingin yliopiston Software Factory -kurssi, jonka aikana toteutettiin asiakasprojekti sulautettua internet-videopuhelujärjestelmää kehittävälle startup-yritykselle. Tapaustutkimuksessa selvitettiin, voidaanko ketterälle vaatimusmäärittelylle tutkimuskirjallisuudessa raportoituja hyötyjä sekä siihen liittyviä haasteita havaita ketterällä menetelmällä toteutettavassa ohjelmistoprojektissa. Tapaustutkimuksen avulla voitiin empiirisesti havaita kaikki vaatimusmäärittelyn hyödyt sekä yksi epätarkkoihin työmääräarvioihin liittyvä haaste. Tästä voidaan päätellä, että hyötyjen saavuttaminen on mahdollista pienellä tiimillä toteutettavassa asiakasprojektissa, jossa ei ole etukäteen tarkasti määriteltyjä ohjelmiston vaatimuksia. Toisaalta haasteitakin voidaan kohdata jo hyvin lyhyessä ajassa, vaikka rakennettaisiin pientä ja yksinkertaista sovellusta.

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