E-thesis - opinnäytteet ja opinnäytetiivistelmät: Recent submissions

Now showing items 1-20 of 38224
  • Pursi, Annukka (Helsingin yliopisto, 2019)
    This study examines playful encounters in early childhood education between adults and children under the age of three. The role of the adult in facilitating and sustaining playful encounters in a multi-party context is of particular interest. The study consists of a summary and four original articles. The research material consists of video observations (150 h) of naturally occurring interaction between adults and children in one municipal toddler classroom. Taking a conversation analysis (CA) approach, the research addresses three questions: (1) How are multiparty playful encounters observable and recognizable from the flow of interaction? (2) How are multi-party playful encounters organized between adults and children in a toddler classroom? (3) What is the adult’s role in facilitating and sustaining multi-party playful encounters? Methodologically, the research develops analytical terminology and a systematic framework which Early Childhood Education and Care (ECEC) researchers can use to study multi-party playful encounters in natural group-care settings. Theoretically, the research produces new scientific knowledge about the organization of playful and emotional stance taking during adult-child playful encounters. The pedagogical contribution of the research is to explain how adult conduct can shape opportunities for multi-party playful encounters in toddler classrooms. The results contribute to theoretical and pedagogical discussion about adults’ roles in children’s play. Overall, the findings can enhance the understanding of ECEC as ECEPC (Early Childhood Education, Play and Care). The study shows how CA can encourage dialogue with ECEC theory and practice by providing a more detailed picture of practices that are described in stocks of interactional knowledge such as the Finnish National Curriculum guidelines on Early Childhood Education and Care.
  • Lyytinen, Outi (Helsingin yliopisto, 2019)
    Viruses are obligate parasites infecting the cells from all the three domains of life: Bacteria, Archaea and Eukarya. Ribonucleic acid (RNA) viruses contain ribonucleic acid as their genomic element instead of deoxyribonucleic acid (DNA). There are three main types of RNA viruses: positive-sense single-stranded [(+)ssRNA], negative-sense single-stranded [(-)ssRNA] and double-stranded RNA (dsRNA) viruses. This Thesis is focused on revealing molecular details of replication and assembly of two dsRNA viruses: Pseudomonas phage phi6 (phi6) and human picobirnavirus (hPBV). Double-stranded RNA viruses need to carry an RNA-dependent RNA polymerase (RdRp) inside their virion to the host in order to be able to replicate their genome. We characterized the hPBV RdRp enzymatically and structurally and revealed the similarities of this RdRp to the other known small dsRNA virus RdRps like phi6 RdRp, which has been extensively studied. We showed that hPBV RdRp has a canonical cupped right-hand polymerase structure, it can replicate and transcribe homologous and heterologous template RNA in the absence of capsid proteins and it also possesses terminal nucleotidyl transferase activity. This is only the second dsRNA virus RdRp reported with this activity. The assembly of these two viruses is relatively different due to the differences in their structures. Phi6 has three layers and a lipid-protein envelope as its outermost layer whereas hPBV does not have any lipids in its structure and is composed of only one layer of capsid proteins surrounding the dsRNA genome. The assembly of the inner protein layers of phi6 is very well-known whereas as the envelope formation and the assembly of hPBV capsid layer is largely uncharacterized. Our results suggest that hPBV might use a co-assembly of its capsid proteins and genomic RNA precursors as its assembly strategy. The envelope assembly of phi6 was studied expressing phi6 membrane proteins in Escherichia coli bacteria. Our results revealed that only one small membrane protein P9 can induce phi6-specific vesicle formation in E. coli cells. Also, heterologous green fluorescent protein can be added to the vesicles by co-expressing non-structural P12 protein. This study reveals interesting molecular details about the genome replication and assembly of hPBV, a relatively unknown opportunistic human pathogen, and the envelopment process of phi6. These results are biologically interesting and may have also biotechnological applications in the future.
  • Romu, K. R. Ilona (Helsingin yliopisto, 2019)
    This work considers with the origin, age and geological environment of the concealed continental crust of Vestfjella, western Dronning Maud Land, Antarctica (WDML). In the Jurassic, the bedrock of Vestfjella experienced the latest major period of extension and rifting. The WDML Jurassic crust has been correlated with the Karoo Large Igneous Province of Africa, and with the Archean and Proterozoic domains, where exposed, of the Archean Kaapvaal Craton and Mesoproterozoic Natal Belt of Africa. The lamproite-hosted xenoliths investigated in this study show metamorphic (including metasomatic) modification from their primary geochemical composition. In the classification of the examined samples, the mineral mode proved to be superior to geochemical classification in protolith identification. The zircon populations of arc affinity metatonalite, quartz metadiorite and metagranite xenoliths record a thermal event at 1150–590 Ma. However, the evolution of the WDML Proterozoic crust began earlier, in the Mesoproterozoic, with arc magmatism at ca. 1450–1300 Ma. The accretion of arc terrains and development of the continental Namaqua–Natal–Maud belt by the Grenvillean-Kibaran orogeny was followed by the break-up of the Rodinia Supercontinent. Granite crystallization at ca. 1100–1090 Ma and at 1050–990 Ma records crustal anatexis, cooling and Neoproterozoic mylonitic deformation. The Proterozoic zircon ages are similar to the crustal domains in the Natal Belt of southern Africa, the Maud Belt of central Dronning Maud Land and remote Mesoproterozoic basement exposed in the West Falkland Islands and Haag nunataks, West Antarctica. The initial εNd (1450) of +7.1 for a pargasite-rich garnet-free metagabbro and the initial εNd (180) of -8.5 for a garnet-bearing metagabbro resemble the isotopic signature of enriched lithospheric mantle and old enriched crust. The present-day Nd isotope composition of these xenoliths conforms to the array of the Triassic Karoo igneous province gabbroic rocks and granulite xenoliths (Proterozoic or undefined), similar to the Lesotho lower crustal xenoliths. The youngest xenolith zircon age, 165 Ma, records crustal heating and A-type granite magmatism post-dating the Karoo magmatism in WDML. The Vestfjella crust cooled below 300 °C at ca. 100 Ma ago (Rb-Sr). This work provides new direct information on the concealed Precambrian of East Antarctica, the regional geology of East Antarctica and southern Africa, and geological processes in the Vestfjella bedrock. The results may be used to resolve the palaeogeography of the supercontinents Rodinia and Gondwana and to interpret existing and forthcoming chronological, geochemical and geophysical data.
  • Ahola, Marja (Helsingin yliopisto, 2019)
    This study aims to understand and explain prehistoric funerary practices from the perspective of Finnish Stone Age hunter-gatherer and early pastoralist earth graves located in mainland Finland. These structures date primarily from the Late Mesolithic to the end of the Middle Neolithic (ca. 6800–2300 cal BC) and represent a unique challenge to archaeological research. This is because unburnt bone material — including human remains — along with other perishable materials are generally not preserved in the acidic soils of Finland. Accordingly, the only feature that marks a Stone Age earth grave is the presence of ochre or stained soil, sometimes together with grave goods typical for that period. This thesis presents a compilation of material remains and archival information from Stone Age earth grave sites and research material as a whole. This approach aims to demonstrate that, whilst Finnish Stone Age earth graves primarily lack human remains and other perishable materials, we can still gain important new insights into Stone Age funerary practices. Consequently, the objective of this thesis lies in systematically studying the earth grave materials, attempting to understand the rituals behind them, and using these data to interpret mortuary practices and cosmology. Based on the results described and discussed in this thesis, the Stone Age mortuary tradition in the Finnish territory represents a complex set of practices that includes not only the archaeologically visible earth grave tradition, but also other means of ritually disposing of the dead body. Accordingly, when we refer to Stone Age mortuary practices in the Finnish territory, we are not speaking of ‘inhumations in simple pit graves’, but of the material remains of complicated rituals that give meaning to and place death within the cosmology of those people. Indeed, the systematic archaeological research conducted in this thesis revealed that both adults and subadults were given earth graves, a tradition also known from better-preserved Stone Age cemeteries in nearby regions of Finland. Similarly, Stone Age people used — and did not use — certain artefacts or raw materials in their funerary practice, in clearly ritualised ways and, for example, to emphasise the identity of the community. When comparing the data in this thesis to other ritual practices known from that specific period and region, Finnish Stone Age earth graves seem to encode an animistic–shamanistic cosmology. Indeed, similar to, for example, prehistoric rock art sites, the Stone Age hunter-gatherer cemeteries are also situated next to topographic features possibly connected to supernatural powers, whilst the graves themselves were furnished with objects that might have been considered living. Simultaneously, an intentional connection to past generations was also sought by positioning new burials amongst older ones or by reusing old cemeteries. To conclude, even if the Finnish Stone Age earth graves primarily lack human remains and other perishable materials, the graves are not as poorly preserved as one might assume. On the contrary, when the earth grave material was investigated as a whole and subjected both to new analyses and theoretical understanding, we gain important new insights into Stone Age mortuary practices and cosmology.
  • Mercier, Stephanie (Helsingin yliopisto, 2019)
    Over the period Shakespeare was writing there was a fundamental evolution in the meaning of “commodity” from something beneficial or serving one’s interest to something to be sold for personal profit. One important aspect of Shakespeare’s theatre is its ability to show how the new notion of “commodity” could also mean trading men and women. Commodity can, therefore, already be associated with “commodification” (OED 1974). Moreover, the process can be recognised across the social scale. The social values of early modern society as mirrored in Shakespeare’s theatre, rather than being an individual matter, are thus shown to be part of a collective process. As studies have shown, the most obvious early modern human commodity was the prostitute and, through association with the Southwark district of London, where Shakespeare’s works were being performed, so were the “hired men”, or players. Yet, Shakespeare’s theatre accords a degree of agency (the ability to make choices and act on those choices) to both, especially women, who were considered as belonging to men (either their fathers or husbands) or as prostitutes, but who are nonetheless given some space for manoeuvre by the playwright. The same cannot always be said for male characters when they come into contact with commodity. In Shakespeare’s plays, where commodity is often at the core of power relations, male authority is shown to be frail and corrupt; it becomes deviant and often makes male characters subservient to unjust laws or demonstrate dishonourable behaviour. In this thesis I show that once authority has been decentred by commodity for profit, it can be further destabilised across society. Shakespeare’s male characters are thus shown to be as objectified as their female counterparts. The phenomenon was already a familiar one within the army, since soldiers had for centuries been mere cannon fodder. It is significant that commodification also affects other male characters, who seem, at best, submissive dupes to commodity (they are either their own victims of commodity desire or gulls to commodity scams) or, at worst, commodified themselves. Even the soldier-king is not exempt from a substantial loss of agency in Shakespeare’s representation of England’s feudalistic culture being replaced by mercantilism. I approach the representation of commodity empirically and from a variety of theoretical perspectives: essentially Gender Studies, New Economic Criticism and Close Reading. I demonstrate that “commodity” was a textual and physical source of structural alteration that was itself undergoing important changes. I show that Shakespeare’s was a theatre of commodities regardless of status and rank. Moreover, Shakespeare approaches commodity from a variety of perspectives, ranging from the comic and light-hearted, to the serious, derisive, and tragic. Most importantly, as commodity becomes increasingly perceptible on stage, some characters lose sight of themselves while others better manage to adjust to the increasing predisposition for commodities. In short, I explore three essential questions: What does Shakespeare’s representation of commodity show us about early modern society? How does Shakespeare’s representation of commodity relate to wider significations of value? Why should we consider the issue on a societal rather than an individual level?
  • Halin, Mikko (Helsingin yliopisto, 2019)
    Graphs are an intuitive way to model connections between data and they have been used in problem solving since the 18th century. In modern applications graphs are used, e.g., in social network services, e-commerce sites and navigation systems. This thesis presents a graph-based approach for handling data and observing identities from network traffic.
  • Karikoski, Antti (Helsingin yliopisto, 2019)
    Data compression is one way to gain better performance from a database. Compression is typically achieved with a compression algorithm, an encoding or both. Effective compression directly lowers the physical storage requirements translating to reduced storage costs. Additionally, in case of a data transfer bottleneck where CPU is data starved, compression can yield improved query performance through increased transfer bandwidth and better CPU utilization. However, obtaining better query performance is not trivial since many factors affect the viability of compression. Compression has been found especially successful in column oriented databases where similar data is stored closely in physical media. This thesis studies the effect of compression on a columnar storage format Apache Parquet through a micro benchmark that is based on the TPC-H benchmark. Compression is found to have positive effects on simple queries. However, with complex queries, where data scanning is relatively small portion of the query, no performance gains were observed. Furthermore, this thesis examines the decoding performance of the encoding layer that belongs to a case database, Fastorm. The goal is to determine its efficiency among other encodings and whether it could be improved upon. Fastorm's encoding is compared against various encodings of Apache Parquet in a setting where data is from a real world business. Fastorm's encoding is deemed to perform well enough coupled with strong evidence to consider adding delta encoding to its repertoire of encoding techniques.
  • Lehvä, Jyri (Helsingin yliopisto, 2019)
    Consumer-Driven Contract testing is a way to test integrations between services. The main idea is that when an application or a service (consumer) consumes an API provided by another service (provider) a contract is formed between them. The contract contains information about how the consumer calls the provider and what the consumer needs from the responses. The contract can then be used to test both sides of the integration separately. The testing method is said to be useful when testing integration-heavy systems such as systems based on microservice architecture. Therefore the research question of the thesis is: "with a focus on integrations, is Consumer-Driven Contract testing a viable addition to a testing strategy used to test a system based on microservice architecture, and if so, why?" The research question is first approached by taking a look at the most recent literature. The goal is to learn about different testing methods and create a basic understanding of a general testing strategy for microservices. The next step is to figure out how the Consumer-Driven Contract testing fits that picture. The Consumer-Driven Contract testing is introduced thoroughly to gain a good understanding of its core concepts, advantages, disadvantages, and tooling. After the literature check, the research question is approached by introducing a case study based on a microservice architecture. Its testing strategy is described in detail, and Consumer-Driven Contract tests are implemented for it. The testing methods are compared by systematically implementing defects to the integrations and seeing how the testing methods catch them. Finally, the results and experiences are shared and analyzed, and the research question gets answered. The results based on literature and experiences from the case study proved that the Consumer-Driven Contract testing is a viable way to test integrations. The tests implemented in the case study caught every defect from the integrations, and the case study was able to verify the advantages mentioned in the literature. It was shown that the Consumer-Driven Contract tests could replace the more traditional integration tests completely. That results to more deterministic testing strategy as the integrations are tested in isolation. It should be emphasized that the teams have to be able to communicate with each other to implement and achieve the benefits of Consumer-Driven Contract testing. The level of communication between the teams has to be mature enough to share the contracts and to coordinate the implementation. Communication is the foundation that enables or disables the testing method. Because of that improving the ways of communication should be a major focus for the teams who want to implement Consumer-Driven Contract tests.
  • Kontio, Heikki (Helsingin yliopisto, 2019)
    The number of IoT sensors is steadily rising in the world. As they're being used more and more in industries and households, the importance of proper lifecycle management (LCM) is increasing. Failure detection and security management are essential to be able to manage the large number of devices. In this thesis a number of platforms are evaluated, on the basis of meeting the expectations of LCM. The evaluation was done via a gap analysis. The categories for the analysis were: tools for estimating the remaining useful lifetime for sensors, API availability for LCM, failure detection and security management. Based on the gap analysis a list of recommendations is given in order to fill the gaps: - universal, platform-independent tools for estimating the remaining useful lifetime (RUL) - update APIs to widely used scalable and extensible architectural style REST - platform-independent standard for sensors reporting health status - industry-standard detection methods available for all
  • Panchamukhi, Sandeep (Helsingin yliopisto, )
    Time series analysis has been a popular research topic in the last few decades. In this thesis, we develop time series models to investigate short time series of count data. We first begin with Poisson autoregressive model and extend it to capture day effects explicitly. Then we propose hierarchical Poisson tensor factorization model as an alternative to the traditional count time series models. Furthermore, we suggest acontext-based model as an improvement over hierarchical Poisson tensor factorization model. We implement the models in an open-source probabilistic programming framework Edward. This tool enables us to express the models in form of executable program code and allows us to rapidly prototype models without the need of derivation of model specificupdaterules. We also explore strategies for selecting the best model out of alternatives. We study the proposed models on a dataset containing media consumption data. Our experimental findings demonstrate that the hierarchical Poisson tensor factorization model significantly outperforms the Poisson autoregressive models in predicting event counts. We also visualize the key results of our exploratory data analysis.
  • Bigler, Paula (Helsingin yliopisto, 2019)
    Viiankiaapa mire, located in the municipality of Sodankylä, has drawn public attention after mining company, AA Sakatti Mining Oy published their discovery in 2011. The discovered Ni-Cu-PGE ore deposit, Sakatti, is located mainly under the Natura 2000 protected Viiankiaapa. Viiankiaapa is Natura 2000 protected due to the several natural habitat types and plant species one of these, H. vernicosus is known to thrive at the areas of groundwater influence. The Sakatti deposit is in exploration phase but it is possible that mining will start in future. Knowing the hydrogeology of the area is crucial for preventing possible negative changes if the mining starts. In this study the objectives were to study 1) the influence of groundwater at the western margin of Viiankiaapa, 2) the influence of Sakatti ore deposit to the hydrogeochemistry of the area, 3) the influence of hydrology and hydrogeochemistry to the endangered H. vernicosus species. The sampling was done in September and October 2016, March and April 2017 and continued in summer 2017. Samples were collected from surface water of the mire, groundwater, spring water as well as from different depth of peat pore water using mini-piezometer. EC, pH, temperature, stable isotopes, DSi, main ions, trace elements and dissolved organic carbon (DOC) were analyzed. The groundwater influence was visible at the area of Lake Viiankijärvi and Särkikoskenmaa fluvial sediment deposit. Depth profiles of stable isotopes and main ions indicated groundwater flow in deep peat layer and mixing with surface water as the groundwater flow upwards through the peat layer. At the Sakatti ore deposit area the isotopic composition of surface water samples represented mainly season’s precipitation with few exceptions. Possible groundwater discharge was visible at the area between Sakatti main deposit and River Kitinen as well as near Pahanlaaksonmaa. The isotopic chemistry of spring water samples at the bend of River Kitinen had values of mixed groundwater and surface water. It is likely that the mire water infiltrates through the peat layer and fluvial sediments and discharges to the springs and River Kitinen. The bedrock of the area is known to be weathered, which could explain surface water like isotope values in springs and in some of the bedrock groundwater observation wells. Positive correlation was found between H. vernicosus ecosystems and the depth of peat. A ribbon-shaped zone of habitats and 2 – 4 m thick peat layer crosses the mire. The correlation with groundwater discharge was not clear. Ca and Mg concentrations were smaller but pH and alkalinity were higher at the areas of H. vernicosus ecosystems. However the Ca and Mg concentrations resembled areal spring water chemistry, which could indicate groundwater influence. Areas without the ecosystems are located mainly near the Sakatti ore deposit. The influence of the deposit in hydrogeochemistry was locally visible as elevated electric conductivity, main ion and trace element concentrations of the surface water and peat pore water. This most likely explains why the areas without the ecosystems had higher element concentrations.
  • Ahlskog, Niki (Helsingin yliopisto, 2019)
    Progressiivisen web-sovelluksen (Progressive Web Application, PWA) tarkoitus on hämärtää tai jo- pa poistaa raja sovelluskaupasta ladattavan sovelluksen ja normaalin verkkosivuston välillä. PWA- sovellus on kuin mikä tahansa normaali verkkosivusto, mutta se täyttää lisäksi seuraavat mitta- puut: Sovellus skaalautuu mille tahansa laitteelle. Sovellus tarjotaan salatun yhteyden yli. Sovellus on mahdollista asentaa puhelimen kotinäytölle pikakuvakkeeksi, jolloin sovellus avautuu ilman se- laimesta tuttuja navigointityökaluja ja lisäksi sovelluksen voi myös avata ilman verkkoyhteyttä. Tässä työssä käydään läpi PWA-sovelluksen rakennustekniikoita ja määritellään milloin sovellus on PWA-sovellus. Työssä mitataan PWA-sovelluksen nopeutta Service Workerin välimuistitallen- nusominaisuuksien ollessa käytössä ja ilman. PWA-sovelluksen luomista ja käyttöönottoa tarkastel- laan olemassa olevassa yksityisessä asiakasprojektissa. Projektin tarkastelussa kiinnitetään huomio- ta PWA-sovelluksen tuomiin etuihin ja kipupisteisiin. Tuloksen arvioimiseksi otetaan Google Chromen Lighthouse -työkalua käyttäen mittaukset sovel- luksen progressiivisuudesta ja nopeudesta. Lisäksi sovellusta vasten ajetaan Puppeteer-kirjastoa hyödyntäen latausnopeuden laskeva testi useita kertoja sekä tarkastellaan PWA-sovelluksen Service Workerin välimuistin hyödyllisyyttä suorituskyvyn ja latausajan kannalta. Jotta Service Workerin välimuistin käytöstä voidaan tehdä johtopäätökset, nopeuden muutosta tarkastellaan progressii- visten ominaisuuksien ollessa käytössä ja niiden ollessa pois päältä. Lisäksi tarkastellaan Googlen tapaustutkimuksen kautta Service Workerin vaikutuksia sovelluksen nopeuteen. Testitulokset osoittavat että Service Workerin välimuistin hyödyntäminen on nopeampaa kaikissa tapauksissa. Service Workerin välimuisti on nopeampi kuin selaimen oma välimuisti. Service Worker voi myös olla pysähtynyt ja odotustilassa käyttäjän selaimessa. Silti Service Workerin aktivoimi- nen ja välimuistin käyttäminen on nopeampaa kuin selaimen välimuistista tai suoraan verkosta lataaminen.
  • Rodriguez Villanueva, Cesar Adolfo (Helsingin yliopisto, 2019)
    Spam detection techniques have made our lives easier by unclogging our inboxes and keeping unsafe messages from being opened. With the automation of text messaging solutions and the increase in telecommunication companies and message providers, the volume of text messages has been on the rise. With this growth came along malicious traffic which users had little control over. In this thesis, we present an implementation of a spam detection system in a real-world text messaging platform. Using well-established machine learning algorithms, we make an in-depth analysis on the performance of the models using two different datasets: one publicly available (N=5,574) and the other gathered from actual traffic of the platform (N=1,477). Making use of the empirical results, we outline the models and hyperparameters which can be used in the platform and in which scenarios they produce optimal performance. The results indicate that our dataset poses a great challenge at accurate classification, most likely due to the small sample size and unbalanced dataset, along with nuances in the dataset. Nevertheless, there were models that were found to have a good all-around performance and they can be trained and used in the platform.
  • Martikainen, Jussi-Pekka (Helsingin yliopisto, 2019)
    Wood is the fuel for the forest industry. Fellable wood is collected from the forests and requires transportation to the mills. The distance to the mills is quite often very long. The most used long- distance transportation means of wood in Finland is by road transportation with wood-trucks. The poor condition of the lower road network increases the transportation costs not only for the forest industry but for the whole natural resources industry. Timely information about the conditions of the lower road network is considered beneficial for the wood transportation and for the road maintenance planning to reduce the transportation related costs. Acquisition of timely information about the conditions of the lower road network is a laborious challenge to the industry specialists due to the vast size of the road network in Finland. Until the recent development in ubiquitous mobile computing collecting the road measurement data and the detection of certain road anomalies from the measurements has traditionally required expensive and specialized equipment. Crowdsensing with the capabilities of a modern smartphone is seen as inexpensive means with high potential to acquire timely information about the conditions of the lower road network. In this thesis a literature review is conducted to find out the deteriorative factors behind the conditions of the lower road network in Finland. Initial assumptions are drawn about the detectability of such factors from the inertial sensor data of a smartphone. The literature on different computational methods for detecting the road anomalies based on the obtained accelerometer and gyroscope measurement data is reviewed. As a result a summary about the usability of the reviewed computational methods for detecting the reviewed deteriorative factors is presented. And finally suggestions for further analysis for obtaining more training data for machine learning methods and for predicting the road conditions are presented.
  • Aula, Kasimir (Helsingin yliopisto, 2019)
    Air pollution is considered to be one of the biggest environmental risks to health, causing symptoms from headache to lung diseases, cardiovascular diseases and cancer. To improve awareness of pollutants, air quality needs to be measured more densely. Low-cost air quality sensors offer one solution to increase the number of air quality monitors. However, they suffer from low accuracy of measurements compared to professional-grade monitoring stations. This thesis applies machine learning techniques to calibrate the values of a low-cost air quality sensor against a reference monitoring station. The calibrated values are then compared to a reference station’s values to compute error after calibration. In the past, the evaluation phase has been carried out very lightly. A novel method of selecting data is presented in this thesis to ensure diverse conditions in training and evaluation data, that would yield a more realistic impression about the capabilities of a calibration model. To better understand the level of performance, selected calibration models were trained with data corresponding to different levels of air pollution and meteorological conditions. Regarding pollution level, using homogeneous training and evaluation data, the error of a calibration model was found to be even 85% lower than when using diverse training and evaluation pollution environment. Also, using diverse meteorological training data instead of more homogeneous data was shown to reduce the size of the error and provide stability on the behavior of calibration models.
  • Luhtakanta, Anna (Helsingin yliopisto, 2019)
    Finding and exploring relevant information from a huge amount of available information is crucial in today’s world. The information need can be a specific and precise search or a broad exploratory search, or even something between the two. Therefore, an entity-based search engine could provide a solution for combining these two search goals. The focus in this study is to 1) study previous research articles on different approaches for entity-based information retrieval and 2) implement a system which tries to provide a solution for both information need and exploratory information search, regardless of whether the search was made by using basic free form query or query with multiple entities. It is essential to improve search engines to support different types of information need in the incessantly expanding information space.
  • Suomalainen, Lauri (Helsingin yliopisto, 2019)
    Hybrid Clouds are one of the most notable trends in the current cloud computing paradigm and bare-metal cloud computing is also gaining traction. This has created a demand for hybrid cloud management and abstraction tools. In this thesis I identify shortcomings in Cloudify’s ability to handle generic bare-metal nodes. Cloudify is an open- source vendor agnostic hybrid cloud tool which allows using generic consumer-grade computers as cloud computing resources. It is not however capable to automatically manage joining and parting hosts in the cluster network nor does it retrieve any hardware data from the hosts, making the cluster management arduous and manual. I have designed and implemented a system which automates cluster creation and management and retrieves useful hardware data from hosts. I also perform experiments using the system which validate its correctness, usefulness and expandability.
  • Nietosvaara, Joonas (Helsingin yliopisto, 2019)
    We examine a previously known sublinear-time algorithm for approximating the length of a string’s optimal (i.e. shortest) Lempel-Ziv parsing (a.k.a. LZ77 factorization). This length is a measure of compressibility under the LZ77 compression algorithm, so the algorithm also estimates a string’s compressibility. The algorithm’s approximation approach is based on a connection between optimal Lempel-Ziv parsing length and the number of distinct substrings of different lengths in a string. Some aspects of the algorithm are described more explicitly than in earlier work, including the constraints on its input and how to distinguish between strings with short vs. long optimal parsings in sublinear time; several proofs (and pseudocode listings) are also more detailed than in earlier work. An implementation of the algorithm is provided. We experimentally investigate the algorithm’s practical usefulness for estimating the compressibility of large collections of data. The algorithm is run on real-world data under a wide range of approximation parameter settings. The accuracy of the resulting estimates is evaluated. The estimates turn out to be consistently highly inaccurate, albeit always inside the stated probabilistic error bounds. We conclude that the algorithm is not promising as a practical tool for estimating compressibility. We also examine the empirical connection between optimal parsing length and the number of distinct substrings of different lengths. The latter turns out to be a suprisingly accurate predictor of the former within our test data, which suggests avenues for future work.
  • Raitahila, Iivo (Helsingin yliopisto, 2019)
    The Internet of Things (IoT) consists of physical devices, such as temperature sensors and lights, that are connected to the Internet. The devices are typically battery powered and are constrained by their low processing power, memory and low bitrate wireless communication links. The vast amount of IoT devices can cause heavy congestion in the Internet if congestion is not properly addressed. The Constrained Application Protocol (CoAP) is an HTTP-like protocol for constrained devices built on top of UDP. CoAP includes a simple congestion control algorithm (DefaultCoAP). CoAP Simple Congestion Control/Advanced (CoCoA) is a more sophisticated alternative for DefaultCoAP. CoAP can also be run over TCP with TCP's congestion control mechanisms. The focus of this thesis is to study CoAP's congestion control. Shortcomings of DefaultCoAP and CoCoA are identified using empirical performance evaluations conducted in an emulated IoT environment. In a scenario with hundreds of clients and a large buffer in the bottleneck router, DefaultCoAP does not adapt to the long queuing delay. In a similar scenario where short-lived clients exchange only a small amount of messages, CoCoA clients are unable to sample a round-trip delay time. Both of these situations are severe enough to cause a congestion collapse, where most of the link bandwidth is wasted on unnecessary retransmissions. A new retransmission timeout and congestion control algorithm called Fast-Slow Retransmission Timeout (FASOR) is congestion safe in these two scenarios and is even able to outperform CoAP over TCP. FASOR with accurate round-trip delay samples is able to outperform basic FASOR in the challenging and realistic scenario with short-lived clients and an error-prone link.
  • Huovinen, Ilmari (Helsingin yliopisto, 2019)
    Jatkuva kehitys on joukko ohjelmistokehitysmenetelmiä, jotka mahdollistavat julkaisujen tekemisen luotettavasti ja tiheään tahtiin. Jatkuva kehitys sisältää useita menetelmiä, mutta niistä kolme laajasti tunnettua ovat jatkuva integraatio, jatkuva toimitus ja jatkuva julkaisu. Jatkuvassa integraatiossa muutokset integroidaan jatkuvasti yhteiseen koodikantaan, jatkuvassa toimittamisessa muutokset toimitetaan jatkuvasti tuotantoa muistuttavaan ympäristöön ja jatkuvassa julkaisussa muutokset julkaistaan jatkuvasti. GameRefinery on pelialan yritys, joka kehittää mobiilipelien analyysi- ja markkinadataa tarjoavaa SaaS-palvelua. Palvelun kasvaessa on huomattu haasteita sen kehittämisessä ja ylläpidossa. Tämän tutkielman tarkoituksena selvittää mitä kehitykseen ja julkaisuun liittyviä ongelmia GameRefinery SaaS:ssa on koettu, ja sunnitella jatkuvan kehityksen menetelmiä käyttävä prosessi korjaamaan koettuja ongelmia. GameRefinery SaaSin kehitykseen ja julkaisuun liittyviä ongelmat etsittiin tutkimalla GameRefinery SaaSin aiempia versioita ja selvittämällä mitkä niiden ratkaisut haittasivat ohjelmiston kehitystä ja julkaisua ja mitkä tukivat niitä. Tämän jälkeen verrattiin eroja GameRefinery SaaSin versioiden kehitys- ja julkaisuprosesseissa. Lopuksi eriteltiin löydetyt kehitykseen ja julkaisuun liittyvät ongelmat. Ongelmia löydettiin versiohallintakäytännöistä, toimitus- ja julkaisuprosessista ja virheistä palautumisessa. Lisäksi huomattiin, että arkkitehtuurinen ratkaisu siirtää eräajot pois mikropalveluista omiksi projekteikseen aiheutti ongelmia julkaisujen tekemisessä. Löydettyjä ongelmia ratkaistiin suunnittelemalla jatkuvan kehityksen prosessi, joka perustui Jenkins-automaatiopalvelimen käyttöönottamiseen ja jatkuvan kehityksen menetelmiä hyödyntävän automaatioputken toteuttamiseen. Suunniteltu prosessi selvensi version- ja haaranhallinta käytäntöjä, korjaten ongelmia julkaisuversioiden kasaamisessa eri ominaisuuksista ja estämällä keskeneräisen koodin pääsemisen julkaisuhaaraan. Uudessa prosessissa myös automatisoitiin toimitusprosessi niin, että tietomallin muokkaus otettiin osaksi automaatioputkea poistaen aikaisemmin manuaalisesti suoritetun vaiheen toimituksessa. Näiden lisäksii esitettiin mahdolliset ongelmatilanteet virheestä palautumisessa ja tapoja korjata niitä. Uusi prosessi ei kuitenkaan onnistunut korjaamaan eräajojen siirtämisestä aiheutuneita ongelmia, vaikkakin eräajojen mukaan ottaminen automaatioputkeen lievensi niitä.