Matemaattis-luonnontieteellinen tiedekunta


Nyligen publicerat

  • Jyrkänkallio-Mikkola, Jenny (Helsingin yliopisto, 2018)
    Freshwaters harbour disproportionally high biodiversity in relation to their area. Yet, they are among the most threatened ecosystems on Earth due to the increasing anthropogenic pressures. The ongoing climate change and Holocene extinctions give rise to an increasing need for conservation efforts in order to avoid future species losses. Successful conservation attempts require a comprehensive understanding how species and communities are distributed in space and time. There are notable gaps in the knowledge of diversity gradients of hyperdiverse microbes and invertebrates, and this knowledge gap is more pronounced in the tropics. This thesis seeks to 1) investigate the effects of local environmental, catchment characteristics, spatial and climatic factors on stream communities across sites and catchments; 2) examine benthic diatom diversity patterns and the underlying factors within and among streams and stream orders; 3) examine the effect of environmental heterogeneity on benthic diatom beta diversity and; 4) compare the diversity patterns of stream diatoms and insects between boreal and tropical regions. To accomplish these aims, microbial and insect communities were collected from boreal and tropical regions and the underlying causes of community spatial variation were investigated using advanced statistical methods. The thesis demonstrated that stream communities are driven by a range of factors acting on multiple spatial scales. Water chemistry, stream physical variables, biotic interactions, land use, spatial and climatic factors contributed to the variation in stream community composition and taxonomic richness. Diatom community composition exhibited significant within- and among-stream variation at intermediate spatial scales, which has relevance for biomonitoring using diatoms. Headwater streams exhibited higher beta diversity and harboured regionally unique diatom communities, which encourages the conservation of headwater streams. It was further demonstrated that environmental heterogeneity promotes diatom beta diversity, which emphasizes the role of habitat heterogeneity in sustaining diverse communities. Somewhat surprisingly, diatom species richness was not higher in the tropics than in the boreal study region, and a notable number of diatom species were found from both regions. This implies that diatoms may not follow the traditional global latitudinal diversity gradient and further suggests that some diatom species exhibit global distributions. Insect genus richness was slightly higher in the tropics than in the boreal study region, whereas insect abundance was significantly higher in the boreal than the tropical region. The large within-region variation in insect genus richness and abundance may be more strongly driven by factors operating at regional scale than by the region itself, further suggesting that streams exhibit uniqueness and do not fit well into predefined categories based purely on latitude. In summary, this thesis increases knowledge of the underlying variables affecting stream community variation. Further, biomonitoring and conservational efforts may benefit from the identified factors contributing to regional stream diversity. Finally, this thesis increases knowledge and understanding of the similarities and differences of stream communities across regions.
  • Gong, Yongmei (Helsingin yliopisto, 2018)
    Ice shelves and ice caps constitute a great proportion of the glacial ice mass that covers 10% of the global land surface and is vulnerable to climate change. Large scale ice flow models are widely used to investigate the mechanisms behind the observed physical processes and predict their future stability and variability under climate change. This thesis aims at providing general remarks on the application of ice flow models in studying glaciological problems through investigating the evolution of an Antarctic ice shelf under climate change and the mechanisms of fast ice flowing events (surges) in an Arctic ice cap. In addition discussions of the equivalence of two significantly different expressions for the rate factor in Glen’s flow are also provided. Off-line coupling between the Lambert Glacier-Amery Ice Shelf (LG-AIS) drainage system, East Antarctica, and the climate system by employing a hierarchy of models from general circulation models, through high resolution regional atmospheric and oceanic models, to a vertically integrated ice flow model has been carried out. The adaptive mesh refinement technique is specifically implemented for resolving the problem concerning grounding line migration. Sensitivity tests investigating the importance of various parameters and boundary conditions are carried out in ice flow models with different approximations for Austfonna Ice-cap, Svalbard to investigate the surge event in one of its basins, Basin 3. Inverse modelling of basal friction coefficient is specifically implemented. A continuum to discrete multi-model approach is implemented for simulations of Basin 3. LG-AIS drainage system will be rather stable in the face of future warming over 21st and 22nd centuries. Although the ice shelf thins in most of the simulations there is little grounding line retreat. The change of ice thickness and velocity in the ice shelf is mainly influenced by the basal melt distribution. And the Lambert, Fisher and Mellor glaciers are most sensitive to thinning of the ice shelf south of Clemence Massif. The sea level rise contribution of LG-AIS is modest as the increased accumulation computed by the atmosphere models outweighs ice stream acceleration. Using a temporally fixed basal friction field obtained through inverse modelling is insufficient to simulate the future changes of the fast flowing surging glacier in Basin 3. And the evolution of basal friction patterns, and in turn basal processes are among the most important factors during the surge in Basin 3. A system of processes and feedback involving till deformation and basal hydrology is more likely to explain both the seasonal accelerations and the ongoing inter-annual speed-up more than a hard-bed mechanism. The continuum to discrete multi-model approach provides the possible locations of the crevasses that can potentially cut through the full length of the ice and deliver surface melt water down to the bed. The calculated basal water flow paths according to hydraulic potential indicate that the summer speed up events and the initiation of the acceleration in the southern part of the basin can be explained by either a direct enhancement to the ice flow through basal lubrication or a lagged-in-time mechanism through the outflow of accumulated water in the over-deepening area. Keywords: ice flow modelling, climate change, sea level rise, future projection, basal sliding, basal hydrology, surface melt, surging glacier, Lambert Glacier-Amery Ice Shelf, Austfonna Ice-cap, Antarctic, Svalbard
  • Shang, Yuan (Helsingin yliopisto, 2018)
    Red Clay and overlying loess-palaeosol sequences are typical for the area in northern China that is known as the Chinese Loess Plateau (CLP). These primarily aeolian sediments provide one of the best terrestrial archives of Neogene-Quaternary climate change, and their formation has been linked to the uplift of the Tibetan Plateau, the progressive aridification of East Asia and the onset of and changes in the East Asian monsoon. In the present study, the sediment provenance was reconstructed using a combination of analytical techniques that allowed better understanding of the (long-term) shifts in sediment delivery in response to changes in the climate and tectonic evolution. Zircon U–Pb age spectral and backtrace trajectory modelling of three well-known Red Clay sequences distributed across the CLP revealed spatiotemporal variations in the provenance of late Miocene-Pliocene Red Clay. The results indicate that the Red Clay in the southern and western CLP was mainly derived from the Northern Tibetan Plateau (NTP) and the Taklimakan Desert. In contrast, Red Clay in the northeastern CLP displays a zircon U-Pb age signature of the broad area of the Central Asian Orogenic Belt. In addition, the northeastern Red Clay shows increased contributions from the west around 3.6 Ma, possibly suggesting an intensified westerly wind strength and/or aridity of the NTP and Taklimakan Desert arising from the uplift of the NTP and Tianshan Mountains in the Pliocene. This could also be caused by the onset of enhanced Yellow River drainage in response to the increased NTP denudation since 3.6 Ma. To further investigate the role of the Yellow River in supplying dust to the Quaternary loess deposits, the sedimentology and source signal of the unique loess-palaeosol sequence of the Mangshan Loess Plateau (MLP) along the lower reach of the Yellow River was investigated by end-member modelling of the loess grain-size records and single-grain zircon U-Pb dating. The results suggest that the Yellow River floodplain north of the MLP has served as a major dust source at least since 900 ka. The sudden change in sedimentology (accumulation rate, grain-size distribution) of the Mangshan sequence above palaeosol unit S2 may have been initiated by a combination of tectonic movements in the Weihe Basin and in the Yellow River floodplain north of the MLP around 240 ka. Subsequent rapid fluvial incision in the northern part of the Weihe Basin resulted in increased sediment flux being transported to the lower reach of the Yellow River. Tectonic movements in the floodplain north of the MLP would have caused a southward migration of the Yellow River course, explaining the formation of an impressive scarp and the more proximal location of the sediment source. In addition to provenance analysis, grain size and shape characteristics obtained by dynamic image analysis (DIA) were used to fingerprint the transport processes of silt particles in a series of Quaternary loess-palaeosol sequences. The results revealed a decrease in the aspect ratio of the particles as a function of increasing grain size, thus indicating that systematic shape sorting occurred during the aeolian transport of the silt particles. A similar particle-shape sorting trend has also been found in a series of Red Clay sequences, confirming that the Red Clay deposits are predominantly of aeolian origin. This study indicates that DIA of grain size and shape characteristics can be an additional powerful tool for fingerprinting trends in grain size and shape sorting, determining the dominant mode of transport, and reconstructing the transportation pathways of silt-sized aeolian sediments. The final part of this thesis research comprised a pilot study on the use of the trace-element composition of quartz as a provenance tool to constrain the source area of the late Neogene and Quaternary dust deposits in northern China. It revealed that quartz in the Mangshan loess deposits is largely derived from the Qaidam Basin of the NTP. The likely dust contribution from the Taklimakan Desert to the Red Clay deposits in Baode is also reflected in the trace element content of quartz. These results are comparable with the source signal obtained from the zircon U-Pb age spectra, suggesting that the trace element composition of quartz could be applied as an alternative tool to other single-grain provenance analytical approaches to track the dust source and dust pathways of the aeolian sediments.
  • Nelimarkka, Matti (Helsingin yliopisto, 2018)
    There is a division among computer-supported collaboration tools by location (collocated/ distributed) and by time (synchronous/asynchronous). Collocated synchronous tools were once given focus in research through studies of group support systems. Today, ubiquitous computing has led to collocated synchronous computing becoming a part of day-to-day life. The practices involved take place in hybrid space – a mixture of face-to-face and computer-mediated communication. This very real, concrete phenomenon has been subject to study in the human-computer interaction domain; however, theories examining social interaction in the hybrid space, or hybrid interaction, are rare. Such theories may help to advance the design and utilization of tools for hybrid interaction. Aimed at helping practitioners understand and benefit from hybrid interaction, a study of one form of it was undertaken, with the emphasis on cases wherein the event is organized as a performance and there are spectators and performers. Hence, the focus is on performative hybrid interaction: hybrid interaction that is used as part of a performance. The work builds on 14 instances of hybrid interaction examined through mixed-methods approaches. The following observations about social practices were made on the basis of the empirical research: (i) Hybrid interaction has social rules that govern how interaction takes place. In this respect, hybrid interaction is like any social interaction. However, the social rules of hybrid interaction emerge from the rules of both computer-mediated and face-to-face interaction. These two communication channels are interlinked and, therefore, influence one another. (ii) In performer-oriented settings, it is important to establish social rules that support the performance. Performative hybrid interaction benefits from active guidance by performers. This active guidance establishes the social rules and communicates them to spectators. Performers establish these rules in several ways, both onstage and offstage. Yet the technical systems employed do not scaffold and support the active guidance. (iii) The choices surrounding social rules are normative decisions. Therefore, frameworks that account for and reflect these decisions can be helpful for designers and researchers. Frameworks of this nature might be adapted, for example, from political science. They benefit research and design in two ways. Firstly, they often provide a set of validated empirical methods that make the research more solid. Secondly, they support the design of systems: they justify the design goals and provide a backdrop against which the design ideas evolve. Discussion proceeding from these findings considers how to improve practices of performative hybrid interaction. The thesis project investigated the importance of accounting for these social practices. Also, I propose further tools for supporting these social practices, such as the script. Furthermore, the thesis contributes to the use of social theories for human-computer interaction, with a synthesis of elements from several fields of research: political science, performance studies, event studies, and sociology. This combination offers insights related to the difficulties and potential problems in performative hybrid interaction. It also provides insight into the role of normative decisions that ought to inform designers and researchers working on performative hybrid interaction.
  • Hitruhin, Lauri (Helsingin yliopisto, 2018)
    The thesis” On multifractal spectra of mappings of finite distortion” consist of introductory part and four articles. These articles revolve around stretching and rotational properties of mappings of finite distortion both in pointwise and global situations. In the second and third articles the sharp bounds for pointwise rotation of homeomorphisms with exponentially integrable distortion and homeomorphisms with integrable distortion have been established. The sharpness of these bounds is verified by constructing examples using nested annuli. The proofs for optimal bounds are based on techniques utilizing the modulus of path families. The idea is to find suitable path families and use inequality for moduli to find the correct bounds for rotation. This approach also highlights the correlation between stretching and rotation. Moreover, it can also be used for studying optimal pointwise stretching, where we can sharpen the previously known bound for homeomorphisms with integrable distortion. The method using modulus of path families differs from the methods used for obtaining the optimal bounds for quasiconformal mappings, which was done by Astala, Iwaniec, Prause and Saksman. In the first and fourth articles the maximal size of sets in which mappings of finite distortion can attain some predefined stretching and rotation is studied. Identifying the maximal size for all suitable combinations of stretching and rotation amounts to finding the multifractal spectra. In the first article the previously known bounds for the multifractal spectra of quasiconformal mappings, established by Astala, Iwaniec, Prause and Saksman, were sharpened to the level of the Hausdorff measures. This was done by constructing examples using non self-similar Cantor like sets. In the fourth article the multifractal spectra was studied for homeomorphisms with integrable distortion. Here the optimal bounds for the spectra were given and examples proving sharpness presented. Moreover, as an application a question by Clop and Herron, regarding compression of the Hausdorff measure for homeomorphisms of integrable distortion, was answered. Methods used in the proof for the spectra resemble those used in the pointwise case, but the choice of a suitable path family is more involved in this situation.
  • Gregow, Erik (Erweko, 2018)
    Observationer har varit och är en betydelsefull del i den meteorologiska utvecklingen. Markobservationer är mycket användbara som de är, de tillför väderdata för en specifik punkt. Men de ger ingen information om vad som händer mellan dessa mätpunkter. Med modeller kan man skapa en analys, dvs beräkna och estimera vad som händer mellan dessa observationstationer. Radar och satellit ger data över områden och är en produkt där dess mätningar är analyserade. Till exempel, radar ger en bild av var regnet befinner sig, dvs en analys av nuläget. Med en serie av radar bilder, kan en människa (subjektivt) eller en dator (objektivt) bearbeta denna information så att man får en uppfattning om var regnet kommer att befinna sig inom de närmaste minuterna (även timmarna), dvs en kort progonos även kallat “nowcast”. Detta gäller även i stor utsträckning för övriga observationer, såsom satellit data (molnutbredning) etc. För meteorologiska parametrar såsom temperatur eller vind, är det dock betydligt svårare att göra en sådan nowcast, då dessa påverkas av många andra faktorer och det finns inte en linjär utveckling av dem. För att lösa detta problem finns det prognos-modeller, som löser de fysikaliska och dynamiska ekvationerna så att man kan få en bild av kommande väderparametrar för de kommande timmarna och dygnen. En förutsättning för en bra prognos är att man fångar det initiala väderläget så bra som möjligt. Detta görs med observationer och de introduceras i prognosmodellen via olika tekniker. Här kvarstår ett problem då modeller påverkas av fysikaliska oenigheter då de dynamiska förhållandena är i obalans. Detta resulterar ofta i att modellen under de första timmarna har en “spin-up” effekt där de meteorologiska parametrarna ännu inte är i balans med varandra och de prognostiserade väderförhållandena ännu inte är helt tillförlitliga. Därav spenderas mycket forskning om hur man kan reducera denna spin-up effekt och användandet av nowcast-modeller för att tillföra bästa modell resultat för de närmaste timmarna. I denna avhandling har fokus varit att förbättra den meteorologiska analysen (algoritmer och funktionalitet), genom att använda modellen Local Analysis and Prediction System (LAPS). Ett flertal observationer har använts och deras inbördes påverkan studerats, för att i bästa möjliga mån kombinera information från dessa olika instrument. Fokus har främst varit med avseende på nederbördsmängd och beräkning av meteorologiska parametrar som påverkar vindkraftsenergi. LAPS har även använts experimentellt i nowcasting syfte och som analys för prognos-model, för att förbättra prognoserna i närtid. Studierna har i första hand fokuserat på Finland, med närliggande havsområden och tillhörande observations nätverk och instrumentering. Vi har funnit att genom användandet av mark-stationer, radar och blixtnedslags information så kan man förbättra bestämningen av nederbördsmängden. Användandet av blixtdata ger möjligheten att bestämma nederbörd över områden där det inte finns radar, till exempel över havsområden, vilket förr inte varit möjligt. Därtill har vi med förbättrade LAPS analyser (främst moln relaterade parametrar) och en nyutvecklad modell (LOWICE) påvisat positiva resultat vid beräkning av elproduktionen under vintertid, där man tar i beaktning nedisning av vindkraftverkens rotorblad, vilket sänker effektiviteten.
  • Tsuruta, Aki (Helsingin yliopisto, 2017)
    Ensemble Kalman filter (EnKF) is a useful Bayesian inverse modelling method to make inference of the states of interest from observations, especially in non-linear systems with a large number of states to be estimated. This thesis presents an application of EnKF in estimation of global and regional methane budgets, where methane fluxes are inferred from atmospheric methane concentration observations. The modelling system here requires a highly non-linear atmospheric transport model to convert the state space on to the observation space, and an optimization in both spatial and temporal dimensions is desired. Methane is an important greenhouse gas, strongly influenced by anthropogenic activities, whose atmospheric concentration increased more than twice since pre-industrial times. Although its source and sink processes have been studied extensively, the mechanisms behind the increase in the 21st century atmospheric methane concentrations are still not fully understood. In this thesis, contributions of anthropogenic and natural sources to the increase in the atmospheric methane concentrations are studied by estimating the global and regional methane fluxes from anthropogenic and biospheric sources for the 21st century using an EnKF based data assimilation system (CarbonTracker Europe-CH4 ; CTE-CH4). The model was evaluated using assimilated in situ atmospheric concentration observations and various non-assimilated observations, and the model sensitivity to several setups and inputs was examined to assess the consistency of the model estimates. The key findings of this thesis include: 1) large enough ensemble size, appropriate prior error covariance, and good observation coverage are important to obtain consistent and reliable estimates, 2) CTE-CH4 was able to identify the locations and sources of the emissions that possibly contribute significantly to the increase in the atmospheric concentrations after 2007 (the Tropical and extra Tropical anthropogenic emissions), 3) Europe was found to have an insignificant or negative influence on the increase in the atmospheric CH4 concentrations in the 21st century, 4) CTE-CH4 was able to produce flux estimates that are generally consistent with various observations, but 5) the estimated fluxes are still sensitive to the number of parameters, atmospheric transport and spatial distribution of the prior fluxes.
  • Wirtanen, Tom (Helsingin yliopisto, 2017)
    The research of this thesis was initiated when we made an unexpected discovery that a carbon support of a heterogeneous catalyst, which was assumed to be inert, was capable of oxidatively coupling indoles. We later showed, that carbonyls / quinones were formed on the carbon that could act as a redox mediator for this reaction. The results of this work are based on three peer-reviewed publications. In publications I and II, the oxidative power of heterogeneous quinones is established and harnessed for the synthesis of new carbon-carbon sp2 bonds between two organic molecules. In the third publication, this discovered reactivity is transferred to homogeneous conditions. In this research, both heterogeneous and homogeneous quinones were used. Although the underlying chemistry between them is similar, they still form two different conceptual entities and therefore the discussion is also divided into two separate parts: homogeneous and heterogeneous quinones. As this thesis and other publications have shown, heterogenous and homogeneous quinone-mediated reactions can be interconnected. Therefore, the scientific importance of this dissertation is not in the different kinds of organic transformations per se, but in showing that the transformations are accessible with the both heterogeneous and homogeneous quinones.
  • Järvinen, Terhi (Helsingin yliopisto, 2017)
    Two precision measurements are performed to Bs data. The primary measurement of the thesis is the effective lifetime of the Bs meson decaying in the J/psi phi(1020) state. The effective lifetime analysis uses 2012 data recorded by the Compact Muon Solenoid (CMS) experiment. The data are collected with a center-of-mass energy of 8 TeV and correspond to an integrated luminosity of 19.7/fb. The effective lifetime is found to be ctau_eff = 443.9 +/- 2.0 (stat.) +/- 1.2 (syst.) um. In addition to the lifetime measurement, the design, validation and performance of the two flavour tagging algorithms are described. The algorithms are developed to improve the precision of the weak mixing phase measurement. Lastly, the results from the weak phase analysis are briefly covered. The flavour tagging studies and the weak phase measurement are also performed with the 2012 data recorded by the CMS experiment.
  • Kuosmanen, Anna (Helsingin yliopisto, 2017)
    The information contained in the genome of an organism, its DNA, is expressed through transcription of its genes to RNA, in quantities determined by many internal and external factors. As such, studying the gene expression can give valuable information for e.g. clinical diagnostics. A common analysis workflow of RNA-sequencing (RNA-seq) data consists of mapping the sequencing reads to a reference genome, followed by the transcript assembly and quantification based on these alignments. The advent of second-generation sequencing revolutionized the field by reducing the sequencing costs by 50,000-fold. Now another revolution is imminent with the third-generation sequencing platforms producing an order of magnitude higher read lengths. However, higher error rate, higher cost and lower throughput compared to the second-generation sequencing bring their own challenges. To compensate for the low throughput and high cost, hybrid approaches using both short second-generation and long third-generation reads have gathered recent interest. The first part of this thesis focuses on the analysis of short-read RNA-seq data. As short-read mapping is an already well-researched field, we focus on giving a literature review of the topic. For transcript assembly we propose a novel (at the time of the publication) approach of using minimum-cost flows to solve the problem of covering a graph created from the read alignments with a set of paths with the minimum cost, under some cost model. Various network-flow-based solutions were proposed in parallel to, as well as after, ours. The second part, where the main contributions of this thesis lie, focuses on the analysis of long-read RNA-seq data. The driving point of our research has been the Minimum Path Cover with Subpath Constraints (MPC-SC) model, where transcript assembly is modeled as a minimum path cover problem, with the addition that each of the chains of exons (subpath constraints) created from the long reads must be completely contained in a solution path. In addition to implementing this concept, we experimentally studied different approaches on how to find the exon chains in practice. The evaluated approaches included aligning the long reads to a graph created from short read alignments instead of the reference genome, which led to our final contribution: extending a co-linear chaining algorithm from between two sequences to between a sequence and a directed acyclic graph.
  • Moreno, Miguel (Helsingin yliopisto, 2017)
    Model theory and set theory are two disciplines of mathematical logic which can be used to study the Borel reducibility hierarchy in the generalized Baire space. These two disciplines are connected when the complexity of complete first order theories is studied. Each of these disciplines has its approach to measure the complexity of complete first order theories. The Borel reducibility hierarchy in the generalized Baire space shows us a deep connection between these two approaches. In Shelah's stability theory, a classifiable theory is a theory with an invariant that determines the structures up to isomorphisms, a theory with no invariant of this kind is a non-classifiable theory. This tell us that a theory with an invariant of this kind is less complex than a theory with no invariant of this kind. Shelah's stability theory tells us that every countable complete first-order classifiable theory is less complex than all countable complete first-order non-classifiable theories. The subject of study in this thesis is the question: Are all classifiable theories less complex than all the non-classifiable theories, in the Borel reducibility hierarchy? There are two frames where this question can be studied, the generalized Baire space and the generalized Cantor space. It is known that for every theory T, the isomorphism relation of T in the generalized Cantor space and the isomorphism relation of T in the generalized Baire space have the same complexity. This gives us the freedom to choose in which space we would like to work. This question was studied by Friedman, Hyttinen, and Kulikov between others, in previous works. Some of the results in those works pointed out that the relation equivalence modulo the non-stationary ideal might be one of the keys to understand the reducibility of the isomorphism relations. The work of Friedman, Hyttinen, and Kulikov leads to two approaches for the main question: Is it provable in ZFC that in the generalized Cantor space, the isomorphism relation of T is Borel reducible to the equivalence modulo the non-stationary ideal, for T a classifiable theory? Is it provable in ZFC that in the generalized Cantor space, the equivalence modulo the non-stationary ideal is Borel reducible to the isomorphism relation of T, for T a non-classifiable theory? Is it provable in ZFC that in the generalized Baire space, the isomorphism relation of T is Borel reducible to the equivalence modulo the non-stationary ideal, for T a classifiable theory? Is it provable in ZFC that in the generalized Baire space, the equivalence modulo the non-stationary ideal is Borel reducible to the isomorphism relation of T, for T a non-classifiable theory? The work of Friedman, Hyttinen, and Kulikov gives a partial answer to this question. At the same time this points out to a question that might be the key to understand the the connection between classification theory and the Borel reducibility hierarchy: Does the equivalence modulo the non-stationary ideal has the same complexity in the generalized Cantor space as in the generalized Baire space? It is known that the isomorphism relations have the same complexity in the generalized Cantor space as in the generalized Baire space. These are the questions studied in this thesis.
  • Oksman, Mimmi (Helsingin yliopisto, 2017)
    The ongoing climate warming has a profound impact on the sensitive Arctic region and the recent changes in Arctic environment have an alarming rate and magnitude. To better understand the changes taking place in the Arctic region, and to project the future impacts of the ongoing climate change, we need to have records of past climate conditions and past interactions between climate system components, which can be obtained using marine proxy records. This work examines ocean surface conditions from high northern latitudes after the Last Glacial Maximum using marine fossil diatom assemblages. Long-term paleoclimatic and -oceanographic records are obtained from northern Svalbard and central-eastern Baffin Bay using quantitative and qualitative diatom analyses, and sediment grain size distribution analysis. An additional focus of this work was to study the ecology of common northern North Atlantic diatom species and define their relationship to environmental variables (aSSTs and sea ice) in order to identify the best indicator species for these environmental variables and to improve their reliability as paleoceanographic indicators. The Baffin Bay study site was investigated for the deglacial period (10−14 kyr BP), and the results suggest a warmer ocean surface in central-eastern Baffin Bay during the cold Younger Dryas period (11.7−12.9 kyr BP) indicating that the ocean was out of phase with atmospheric conditions over Greenland. The warmer conditions were caused by enhanced inflow of Atlantic-sourced waters and increased solar insolation on the Northern Hemisphere, which amplified seasonality over Baffin Bay and had a significant role triggering the ice margin in West Greenland. The paleoceanographic record from northern Svalbard represents the late Holocene (last ca. 4 200 years), and the results show a clear climate shift at 2.5 kyr BP, as the study location changed from stable, glacier-proximal conditions into fluctuating glacier-distal conditions, emphasizing the sensitivity of the Arctic environment to climate oscillations. Understanding diatom species` relationship to environmental variables is essential and this work identifies robust indicators for cold, temperate and warm waters and for sea ice. The results show that not all sea ice-associated species have a statistically significant relationship to sea ice. While this species is often found in sea ice and in the marginal ice zone, its ecology appears to be more complex. The paleoceanographic and –climatic records in this work give new insights to our current knowledge of past climate variability, and reform some of our current understanding of the past climate conditions on a local scale. This work also improves the applicability of the key northern North Atlantic diatom taxa as paleo-indicators, questioning previous knowledge on the ecology of some species and highlighting some important taxonomic issues.
  • Du, Mian (Helsingin yliopisto, 2017)
    The ongoing information explosion has a particular impact on business areas, involving corporate strategy and business decision-making. Business intelligence tools aim to help users to understand market trends, which is critical for their day-to-day operations. For example, it is a typical business intelligence task to effectively obtain accurate and relevant information about the competitor’s activity in the same industry sector. This thesis presents research on a natural language processing system, which aims to address the problem of information overload in the business domain. It uses document filtering, information extraction, and supervised and semi-supervised learning. Input to the system includes news documents from on-line news websites and company press pages. We first demonstrate that a combination of NLP techniques and frequent sequential pattern mining can be used for finding patterns from unstructured natural-language text, i.e., news articles. The patterns relate to a specific domain of news. Evaluation results show that scenario-based summarization can filter out irrelevant documents and also extract important sentences from relevant documents as summaries for pre-defined scenarios in a specific domain. For document-level filtering, this method achieves very high precision, while keeping quite high recall in our study. Next, we present experiments with supervised learning for labelling business-news documents with multiple industry sectors. The main contribution is that combining a named-entity-based rote classifier with the balanced classifiers yields better results than either classifier alone. This method also improves on the best score previously reported, while using the same amount of training data for the rote classifier, and considerably less for the statistical classifiers. We then explore the interplay between company news, social media visibility, and stock prices. Information extracted from on-line news by means of the deep linguistic analysis is used to construct queries to various social media platforms. The main results presented in the thesis demonstrate the interesting correlations between the mentions of a company in the news and the views of its page in Wikipedia. Based on the above research topics, the thesis also presents the design and architecture of a complete decision-support system. The system is an example of using the above research results to extract, analyze and organize information from plain-text news.
  • Alekseychik, Pavel (Helsingin yliopisto, 2017)
    North Eurasia (NE) is recognized as a region of high importance for the global climate change. Large and systematic shifts in temperature and precipitation, predicted for NE, are expected to cause irreversible disturbances in the ecosystem-atmosphere interactions. The region is dominated by natural boreal and arctic ecosystems, which are experiencing increasing levels of anthropogenic influence through environmental pollution (mainly agriculture- and mining-related) and land use change. However, despite the general consensus on the importance of environmental changes in NE, many aspects of the problem remain poorly understood. Due to the great extent of NE, many crucial areas remain inaccessible or lack the required infrastructure, thereby relevant surface-atmosphere exchange measurement data remains scarce. This thesis examines the surface budgets of carbon dioxide and energy of subarctic peatlands, which count among the most important ecosystems in NE owing to their large carbon storage and areal coverage, and their high sensitivity to climate and land use changes. Peatlands are also heterogeneous ecosystems, with large diversity found both internally and between the ecosystem subtypes. Peatland heterogeneity is notable on several characteristic scales, including the single plant, microsite, microtopography element and ecosystem type. Different scales of variation are covered with specific measurement techniques, i.e. plant-scale gas exchange, chamber and eddy-covariance (EC) technique. The latter is in the focus of this work. Aerodynamic roughness length (z0) and photosynthesis rate measured by EC were compared with the plant- and microsite-scale measurements of leaf area index (LAI) and photosynthesis rate. High correspondence between the estimates on different scales was found, indicating that the transition between the upscaled plant and ecosystem-scale estimates is possible, and thus adding credibility to both. In the fen Siikaneva-1, LAI showed a strong linear relationship with z0, while the EC-derived photosynthesis rate closely followed the upscaled plant chamber estimate. Ecosystem-scale EC measurements made in 2015 at a typical raised bog in West Siberian middle taiga (Mukhrino Field Station) revealed a high cumulative May-August net ecosystem exchange (NEE) of 202 gC m-2 and a mean Bowen ratio (ratio of sensible to latent heat flux) of 0.28, which was lower than expected. Inter-site differences in terms of energy balance were investigated for a selection of eight Fennoscandian peatland sites with different mire types and management histories. The site mean Bowen ratio ranged from 0.28 to 1.35, evapotranspiration (ET) from 1.2 to 2.8 mm/day, and the decoupling parameter (Ω, indicating the relative strength of radiation and surface conductance controls on evapotranspiration) from 0.11 to 0.48. Generally, the energy balance and ecosystem features were found to be tightly linked, corroborating the predictability of peatland energy balances across a wide spectrum of ecosystems. Finally, on a yet larger scale, the current measurement station network of the entire NE is discussed. Measurement gaps are identified based on ecosystem type and climate representation by the existing field stations, with the focus on peatlands. Tentative developments for the NE measurement network are proposed.It is established that Siberia is a region very sparsely covered by ecosystem and climate change monitoring sites, especially when state of the art techniques are concerned (e.g. EC).
  • Hippeläinen, Eero (Helsingin yliopisto, 2017)
    In radionuclide therapy, the patient is injected with relatively high amounts of therapeutic radiopharmaceutical which localises to target tissue and emits ionising radiation. Unfortunately, a perfectly targeting radiopharmaceutical has not been discovered and part of the radiopharmaceutical accumulates to healthy tissues, which are also thus irradiated. In order to ensure safe use, the absorbed dose of radiation-sensitive organs must be monitored. The focus of this thesis is on patient specific dosimetry of lutetium-177 (Lu-177) labelled somatostatin analogue Lu-177-DOTA-Tyr3-octreotate (Lu-177-DOTATATE) treatments and development of internal dosimetry software. Lu-177-DOTATATE is a radiopharmaceutical that binds to somatostatin receptors and is used to treat patients with metastatic neuroendocrine tumours. Recent studies have shown significant treatment outcome improvements with Lu-177-DOTATATE when compared to previously used somatostatin analogue treatments. However, the kidneys are the healthy organ which receives the highest amount of radiation dose from Lu-177-DOTATATE treatments and could be the organ that limits the number of treatments a patient can tolerate. In addition, absorbed dose to kidneys varies highly from patient to patient and thus patient specific dosimetry is recommended. Despite many years of dosimetry research and the existence of several published scientific dosimetry tools, there is no clinically validated kidney dosimetry software for Lu-177-DOTATATE treatments. The aim of this thesis was to study quantification accuracy of Lu-177 radionuclide using SPECT/CT imaging and to study mean absorbed doses to kidneys and dose distribution characteristics of Lu-177-DOTATATE. A streamlined voxel level absorbed dose software for clinical practice was developed and validated for kidney dosimetry of Lu-177-DOTATATE treatments. The effect of reconstruction methods on Lu-177 quantification accuracy was studied using an anthropomorphic phantom with known Lu-177 sources. Acquired data were reconstructed using different image compensation methods and results were compared with known source activities in the phantom. It was found that Monte Carlo simulation based scatter compensation and SPECT detector response compensation improved Lu-177 quantification accuracy considerably. Similar findings were also observed with data from patients treated with Lu-177-DOTATATE. A Monte Carlo simulation study was carried out to investigate absorbed dose distribution of Lu-177. Two main findings were that electrons emitted by Lu-177 can be assumed to absorb locally when the resolution of the imaging system is taken into account and the photon cross-irradiation can contribute significantly to total absorbed dose especially in the vicinity of highly active volumes. Using Lu-177-DOTATATE patient data, two different kidney absorbed dose calculation methods were compared. Comparing the mean kidney absorbed dose with the estimated maximum absorbed dose, it was observed that Lu-177-DOTATATE accumulates unevenly to kidney causing significantly heterogeneous dose distribution within kidneys. In addition, a simplified imaging protocol was found to be adequate for dosimetry purposes and was later adopted clinical practice. Combining previous findings new voxel level dosimetry software was developed. The clinical feasibility of the proposed software was tested with digital phantom simulations and reanalysing patient data from Lu-177-DOTATATE treatments. The software was found to be reliable and to speed up and simplify the dosimetry workflow.