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(2024)Sobolev functions generalize the concept of differentiability for functions beyond classical settings. The spaces of Sobolev functions are fundamental in mathematics and physics, particularly in the study of partial differential equations and functional analysis. This thesis provides an overview of construction of an extension operator on the space of Sobolev functions on a locally uniform domain. The primary reference is Luke Rogers' work "A Degree-Independent Sobolev Extension Operator". Locally uniform domains satisfy certain geometric properties, for example there are not too thin cusps. However locally uniform domains can possess highly non-rectifiable boundaries. For instance, the interior of the Koch snowflake represents a locally uniform domain with a non-rectifiable boundary. First we will divide the interior points of the complement of our locally uniform domain into dyadic cubes and use a collection of the cubes having certain geometric properties. The collection is called Whitney decomposition of the locally uniform domain. To extend a Sobolev function to a small cube in the Whitney decomposition one approach is to use polynomial approximations to the function on an nearby piece of the domain. We will use a polynomial reproducing kernel in order to obtain a degree independent extension operator. This involves defining the polynomial reproducing kernel in sets of the domain that we call here twisting cones. These sets are not exactly cones, but have some similarity to cones. Although a significant part of Rogers' work deals extensively with proving the existence of the kernel with the desired properties, our focus will remain in the construction of the extension operator so we will discuss the polynomial reproducing kernel only briefly. The extension operator for small Whitney cubes will be defined as convolution of the function with the kernel. For large Whitney cubes it is enough to set the extension to be 0. Finally the extension operator will be the smooth sum of the operators defined for each cube. Ultimately, since the domain is locally uniform the boundary is of measure zero and no special definition for the extension is required there. However it is necessary to verify that the extension "matches" the function correctly at the boundary, essentially that their k-1-th derivatives are Lipschitz there. This concludes the construction of a degree independent extension operator for Sobolev functions on a locally uniform domain.
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(2024)The MOOC Center of University of Helsinki maintains a learning management system, primarily used in the online courses offered by the Department of Computer Science. The learning management system is being used in more courses, leading to a need for additional exercise types. In order to satisfy this need, we plan to use additional teams of developers to create these exercise types. However, we would like to minimize any negative effects that the new exercise types may have on the overall system, specifically regarding stability and security. In this work, we propose a plugin system for creating new exercise types, and implement it to production system used by real students. The system's plugins are deployed as separate services and use sandboxed IFrames for their user interfaces. Communication with the plugins occurs through the use of HTTP requests and message passing. The designed plugin system fulfilled its aims and worked in its production deployment. Notably, it was concluded that it is challenging for plugins to disrupt the host system. This plugin system serves as an example that it is possible to create a plugin system where the plugins are isolated from the host system.
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(2024)As part of the SAFER2028, ABCRad (Alternative Buffer/Backfill Characterization and Radionuclide Interactions) research project, two alternative bentonite materials supplied by Posiva Oy were investigated in this thesis. The aim of the thesis was to investigate and determine the sorption behavior of these two buffer material candidates, with a deliberate reference to a well- known Na-Wyoming type bentonite serving as a benchmark. In order to closely imitate conditions relevant to repository settings, a synthetic reference water was prepared, and the experiments were conducted within a glove box in N2 atmosphere excluding CO2 and O2. This thesis provides valuable perspectives on the behavior and attributes of the alternative bentonite materials, which is crucial for guiding decisions in the design of repositories for radioactive waste and strategies for managing spent nuclear fuel. More specifically, this thesis provides thermodynamic sorption models (TMS) for two risk-driving radionuclides, uranium (U) and cesium (Cs). Batch sorption isotherms were made using a 1:20 solid-to-liquid ratio including 0.5 g of bentonite in 10 cm3 of reference water. Gamma spectroscopy and Liquid Scintillation Counting (LSC) were employed for the analysis of reaction supernatants. Complementary to these techniques, additional bentonite properties, including Cation Exchange Capacity (CEC) and Exchangeable Cations (EC), were determined. Pre-characterization was done for the bentonites using Fourier Transform Infrared Spectroscopy (FTIR) and the Specific Surface Areas (SSA) were determined. These analyses provide a comprehensive characterization of the alternative backfill materials under investigation. This thesis focuses on combining quantitative sorption data (e.g., distribution coefficient, Kd) with mechanistic understanding (e.g., FTIR spectroscopy). This contributes to an improved understanding of radionuclide sorption mechanisms, thereby bolstering safety considerations. The CEC determined for the bentonites, Laviosa, LMS, and Na-Wyoming were 87 (±0,048) meq/100 g, 95 (±0,34) meq/100 g, and 91 (± 1,23) meq/100 g, respectively. The distribution coefficient (Kd) values of uranium ranged from 130–135 cm3/g with Laviosa and 78–110 cm3/g with LMS, while those of cesium ranged from 130–280 cm3/g with Laviosa and from 150–425 cm3/g with LMS. Cesium demonstrated sorption of 95% within the 10-10 to 10-6 M range, decreasing slightly to 85–95% at concentrations up to 10-2 M. Uranium showed sorption in the range 80–100% across both clays, peaking at lower concentrations and declining at higher concentrations. These data align with those of the reference buffer material, indicating that these bentonites could potentially serve as feasible alternatives if they exhibit additional favorable sorption capacity with other risk-driving radionuclides (e.g., Eu, Ni, Th).
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(2024)Fog has a significant impact on society, by making transportation and aviation industries difficult to operate as planned due to reduced visibility. Studies have estimated that 32 % of marine accidents, worldwide, and 40 %, in the Atlantic Ocean, took place during dense sea fog. Therefore forecasting fog accurately, and allowing society to function, would help mitigate financial losses associated with possible accidents and delays. However, forecasting the complex fog with numerical weather prediction (NWP) models remains difficult for the modelling community. A NWP model typically operates in the resolution of kilometres, when the multiple processes associated with fog (turbulence, cloud droplet microphysics, thermal inversion) have a smaller spatial scale than that. Consequently, some processes need to be simplified and parametrised, increasing the uncertainty, or more computational power is needed to be allocated for them. One of these NWP models is HARMONIE-AROME, which the Finnish Meteorological Institute develops in collaboration with its European colleague institutes. To improve the associated accuracy, a brand new, more complex and expensive, option for processing aerosols in HARMONIE-AROME, is presented. This near-real-time (NRT) aerosol option integrates aerosol concentrations from Copernicus Atmospheric Monitoring Services' NRT forecast into HARMONIE-AROME. The statistical performance of the model's sea fog forecast in the Baltic Sea was studied in a case study using marine observations. The quantitative metric, proportion score, was studied. As a result, a forecast using the NRT option showed a slight deterioration in visibility (0.52 versus 0.59), a neutral improvement in cloud base height (0.52 versus 0.51), and a slight deterioration in 2-meter relative humidity (0.73 versus 0.76) forecasts with respect to the reference option. Furthermore, the score in general remained weak against observations in the case of visibility and cloud base height. In addition, based on qualitative analysis, the spatial coverage of the forecasted sea fog in both experiments was similar to the one observed by the NWCSAF Cloud Type-product. In total, the new aerosol option showed neutral or slightly worse model predictability. However, no strong conclusions should be made from this single experiment sample and more evaluations should be carried out.
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(2024)Ilmatieteen laitoksen ylläpitämä Suomen virallisten sademittarien havaintoverkko on harva ja sen laajentaminen vaatisi enemmän resursseja. Kansalaisten sadehavaintojen hyödyntäminen olisi yksi keino laajentaa havaintoverkkoa ja siten muun muassa parantaa sääennusteiden laatua. Tässä tutkielmassa selvitettiin kansalaisten Netatmo-kesäsadehavaintojen käyttökelpoisuutta Suomessa. Vuosien 2019–2022 kesä-, heinä- ja elokuun Netatmo-sadehavaintojen laatua tutkittiin vertailemalla niitä Ilmatieteen laitoksen automaattisadeasemien havaintoihin. Vertailua tehtiin tilastollisten suureiden, keskiarvon, korrelaation ja absoluuttisen keskivirheen, avulla. Ennen varsinaista analyysia pyrittiin rajauksilla selkeyttämään aineistoa sekä poistamaan siitä selvästi virheellisiä Netatmo-sadeasemia ja -havaintoja, kuten yli 150 mm:n tunti- ja yli 200 mm:n vuorokausisademäärät. Pääsääntöisesti Netatmo-sadehavainnot näyttävät tilastollisten suureiden valossa hyviltä, sillä esimerkiksi 75 % Netatmo- ja lähimpien Ilmatieteen laitoksen asemien välisistä vuorokausisateiden korrelaatioista oli vähintään 0.6. Netatmo-havaintojen välinen vaihtelu oli kuitenkin suurempi kuin Ilmatieteen laitoksen asemien havaintojen, mikä kertoo osan Netatmo-havainnoista olevan virheellisiä. Virheitä löytyi useita erilaisia. Yleisesti monien Netatmo-asemien havaittiin aliarvioivan sademäärää, koska keskimäärin Netatmo-asemat olivat mitanneet sateita vajaat 10 % vähemmän kuin niiden vertailuasemat. Lisäksi Netatmo-asemien havainnoissa oli huomattavasti enemmän pieniä 0.1 mm mittauksia kuin Ilmatieteen laitoksen vertailuasemilla eikä osa asemista ollut mitannut mitään 0.1 mm virhemittauksia lukuunottamatta. Jotkut Netatmo-asemat puolestaan mittasivat yksittäin tai jopa jatkuvasti virheellisiä hyvin suuria sademääriä. Osa asemista myös yliarvioi sademäärää, sillä asemien sateet korreloivat hyvin vertailuasemien sateiden kanssa ollen vain paljon suurempia. Toisaalta joidenkin Netatmo-asemien realistiset sadehavainnot oli mitattu eri aikoihin kuin vertailuasemien sateet, joten asemien koordinaatit voivat olla väärät. Välillä taas Netatmo-havaintojen laatu muuttui ajan myötä, sillä kyse on kansalaisten havainnoista. Asemat saattoivat ensin tuottaa hyviä havaintoja ja sitten huonoja tai päinvastoin. Kaikkiaan Netatmo-kesäsadehavainnot vaikuttavat käyttökelpoisilta, koska suurin osa havainnoista on hyviä. Netatmo-asemat myös saavat suuria sateita kiinni hyvin. Lisäksi huonoja havaintoja korrelaation perusteella tuottavat Netatmo-asemat ovat hajallaan eri puolilla Suomea ja hyviä asemia on kaikkialla enemmän. Koska virheellisiä Netatmo-asemia ja -havaintoja on silti varsin paljon, Netatmo-sadehavainnot tarvitsevat kattavaa laadun varmistusta ennen havaintojen hyödyntämistä. Laadun varmistusta voisi tehdä tämän tutkimuksen tavoin vertailemalla havaintoja tilastollisesti Ilmatieteen laitoksen asemien havaintoihin. Lisäksi Netatmo-havaintoja voisi verrata keskenään.
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(2024)There are two primary types of quantum computers: quantum annealers and circuit model computers. Quantum annealers are specifically designed to tackle particular problems, as opposed to circuit model computers, which can be viewed as universal quantum computers. Substantial efforts are underway to develop quantum-based algorithms for various classical computational problems. The objective of this thesis is to implement algorithms for solving graph problems using quantum annealer computers and analyse these implementations. The aim is to contribute to the ongoing development of algorithms tailored for this type of machine. Three distinct types of graph problems were selected: all pairs shortest path, graph isomorphism, and community detection. These problems were chosen to represent varying levels of computational complexity. The algorithms were tested using the D-Wave quantum annealer Advantage system 4.1, equipped with 5760 qubits. D-Wave provides a cloud platform called Leap and a Python library, Ocean tools, through which quantum algorithms can be designed and run using local simulators or real quantum computers in the cloud. Formulating graph problems to be solved on quantum annealers was relatively straightforward, as significant literature already contains implementations of these problems. However, running these algorithms on existing quantum annealer machines proved to be challenging. Even though quantum annealers currently boast thousands of qubits, algorithms performed satisfactorily only on small graphs. The bottleneck was not the number of qubits but rather the limitations imposed by topology and noise. D-Wave also provides hybrid solvers that utilise both the Quantum Processing Unit (QPU) and CPU to solve algorithms, which proved to be much more reliable than using a pure quantum solver.
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(2024)Ylioppilaskirjoitukset ovat suomalaisen koulutuksen kentällä merkittävä ja laajasti vaikuttava instituutio. 2018 tapahtuneen sähköistymisen myötä ylioppilaskirjoituksissa tapahtui paljon muutoksia, joiden vaikutuksia ei ole vielä tutkittu kovin laajalti. Tässä tutkielmassa jatketaan aiemman opettaja työnsä tutkijana -tutkielman aihetta, ja haetaan ymmärrystä sähköistymisen vaikutuksista fysiikan ylioppilaskirjoituksiin. Fysiikan ylioppilaskirjoituksia tarkastellaan tässä tutkielmassa \emph{uudistetun Bloomin taksonomian} kautta. Taksonomia esitellään ja sen aiempaa käyttöä kasvatustieteessä, sekä erityisesti päättöarvioinnin tutkimuksessa tarkastellaan. Kun taksonomia ymmärretään, siirrytään hyödyntämään sitä fysiikan ylioppilaskirjoitusten tarkastelussa. Uudistettua Bloomin taksonomiaa hyödyntäen analysoidaan yhteensä kaksitoista fysiikan ylioppilaskoetta vuosilta 2015 - 2018 ja 2021 - 2023. Kuusi kokeista edustavat paperikokeiden ajan loppua, ja kuusi uusimpia sähköisiä ylioppilaskokeita. Kokeiden tehtävät analysoidaan ja luokitellaan uudistetun Bloomin taksonomian mukaiseen taksonomiatauluun erityisesti huomioiden hyvän vastauksen piirteiden perusteella tunnettua kunkin tehtävän pistejakaumaa. Näin saadaan tietoa erikseen paperisten ja sähköisten fysiikan ylioppilaskokeiden tehtävien mittaamasta kognitiivisesta osaamisesta, sekä niiden vaatimista tiedon tyypeistä. Analyysin perusteella havaitaan, että fysiikan ylioppilaskokeet mittaavat laajasti erilaisia kognitiivisen osaamisen ja tiedon tasoja, kuitenkin selvästi painottuen ymmärtämistä ja soveltamista mittaaviin tehtäviin. Lisäksi havaitaan, että erityisesti painoarvoa on käsitteellisellä tiedolla ja menetelmätiedolla. Vertaamalla paperikokeiden ja sähköisten kokeiden tuloksia havaitaan, että sähköistymisen yhteydessä ymmärtämistä vaativa osuus tehtäväpisteistä on pienentynyt 11,5 %-yksikköä. Myös muita pienempiä muutoksia havaitaan, mutta ne eivät ole tilastollisesti merkitseviä. Lopuksi tutkielmassa arvioidaan muutosten syitä, erityisesti sähköistymisen tarjoaman laajemman työkaluvalikoiman vaikutusta tehtävänlaadintaan. Toisaalta taksonomiasta luonteesta ja tutkielman koejärjestelystä tunnistetaan puutteita, joiden seurauksena tulosten luotettavuus nousee kyseenalaiseksi.
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(2024)Essential thrombocythemia (ET) is a clonal hematopoietic disease characterized by an abnormal increase of platelets in the circulation, with increased risk of thrombosis and hemorrhage. Despite megakaryocytes having a central role in the disease, few studies have investigated their gene expression in ET. The aim of this study is to characterize the gene expression profiles of megakaryocytes from ET patients harboring different driver mutations, and increase the knowledge of the molecular mechanisms underlying the pathophysiology of the disease. In this study, samples were obtained from healthy donors and ET patients with JAK2 V617F, CALR Type I, CALR Type II driver mutations and triple-negative patients. Following megakaryocyte culture from peripheral blood and RNA sequencing, the data was pre-processed and analyzed using differential gene expression analysis. The downstream analysis was conducted using pathway enrichment analysis tools. The analysis revealed that all mutants shared common deregulated genes related to processes involving platelets and coagulation. However, it was shown that CALR and JAK2 V617F mutants also have distinct patterns of gene expression. CALR Type I mutants had a unique gene expression signature consisting of genes related to immune response, as well as metabolic, regulatory, proliferative, and inflammatory pathways, while CALR Type II mutants had unique genes related to ribosomes. The CALR mutants also shared a common anti-inflammatory response signature which set them apart from JAK2 V617F mutants. In conclusion, this study shows that the gene expression profiles of ET mutants are heterogeneous. Moreover, the results provide new insights into the gene expression profiles of CALR mutants that distinguish them from the other mutants. Further experiments using single-cell RNA sequencing methods could build upon these findings and uncover the observed gene expression discrepancies between CALR and JAK2 mutants with increased accuracy.
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(2024)Statistician C. R. Rao made many contributions to multivariate analysis over the span of his career. Some of his earliest contributions continue to be used and built upon almost eighty years later, while his more recent contributions spur new avenues of research. This thesis discusses these contributions, how they helped shape multivariate analysis as we see it today, and what we may learn from reviewing his works. Topics include his extension of linear discriminant analysis, Rao’s perimeter test, Rao’s U statistic, his asymptotic expansion of Wilks’ Λ statistic, canonical factor analysis, functional principal component analysis, redundancy analysis, canonical coordinates, and correspondence analysis. The examination of his works shows that interdisciplinary collaboration and the utilization of real datasets were crucial in almost all of Rao’s impactful contributions.
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(2024)In this thesis, we prove the existence of a generalization of the matrix product state (MPS) decomposition in infinite-dimensional separable Hilbert spaces. Matrix product states, as a specific type of tensor network, are typically applied in the context of finite-dimensional spaces. However, as quantum mechanics regularly makes use of infinite-dimensional Hilbert spaces, it is an interesting mathematical question whether certain tensor network methods can be extended to infinite dimensions. It is a well-known result that an arbitrary vector in a tensor product of finite-dimensional Hilbert spaces can be written in MPS form by applying repeated singular value or Schmidt decompositions. In this thesis, we use an analogous method in the infinitedimensional context based on the singular value decomposition of compact operators. In order to acquire sufficient theoretical background for proving the main result, we first discuss compact operators and their spectral theory, and introduce Hilbert-Schmidt operators. We also provide a brief overview of the mathematical formulation of quantum mechanics. Additionally, we introduce the reader to tensor products of Hilbert spaces, in both finite- and infinite-dimensional contexts, and discuss their connection to Hilbert-Schmidt operators and quantum mechanics. We also prove a generalization of the Schmidt decomposition in infinite-dimensional Hilbert spaces. After establishing the required mathematical background, we provide an overview of matrix product states in finite-dimensional spaces. The thesis culminates in the proof of the existence of an MPS decomposition in infinite-dimensional Hilbert spaces.
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(2024)Buildings consume approximately 40% of global energy, hence, understanding and analyzing energy consumption patterns of buildings is essential in bringing desirable insights to building management stakeholders for better decision-making and energy efficiency. Based on a specific use case of a Finnish building management company, this thesis presents the challenge of optimizing energy consumption forecasting and building management by addressing the shortcomings of current individual building-level forecasting approaches and the dynamic nature of building energy use. The research investigates the plausibility of a system of building clusters by studying the representative cluster profiles and dynamic cluster changes. We focus on a dataset comprising hourly energy consumption time series from a variety of Finnish university buildings, employing these as subjects to implement a novel stream clustering approach called ClipStream. ClipStream is an attibute-based stream clustering algorithm to perform continuous online clustering of time series data batches that involves iterative data abstraction, clustering, and change detection phases. This thesis shows that it was plausible to build clusters of buildings based on energy consumption time series. 23 buildings were successfully clustered into 3-5 clusters during each two-week window of the period of investigation. The study’s findings revealed distinct and evolving energy consumption clusters of buildings and characterized 7 predominant cluster profiles, which reflected significant seasonal variations and operational changes over time. Qualitative analyses of the clusters primarily confirmed the noticeable shifts in energy consumption patterns from 2019 to 2022, underscoring the potential of our approach to enhance forecasting efficiency and management effectiveness. These findings could be further extended to establish energy policy, building management practices, and broader sustainability efforts. This suggests that improved energy efficiency can be achieved through the application of machine learning techniques such as cluster analysis.
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(2024)Compression methods are widely used in modern computing. With the amount of data stored and transferred by database systems constantly increasing, the implementation of compression methods into database systems has been studied from different angles during the past four decades. This thesis studies the scientific methods used in relational database research. The goal of the thesis is to evaluate the methods employed and to gain an understanding into how research into the subject should be conducted. A literature review is conducted. 14 papers are identified for review and their methodology is described and analysed. The papers reviewed are used to answer four research question and classified according to insights gained during the review process. There are similarities in methods of different papers that can be described to use as a starting point for conducting research in the field of database compression.
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(2024)The question of reunification, or ‘the Taiwan issue’, stands as one of the paramount geopolitical conundrums of the 21st century. China asserts that Taiwan is an inalienable part its historical geo-body and socio-cultural chronicles under the unifying idea of ‘Chineseness’. Nevertheless, since Taiwan’s democratization process began to thrive in the 1990s, perceptions of national identity have diverged drastically from those in mainland China. Corollary, the appeal for reunification in Taiwan is almost non-existent, and hence achieving peaceful unification under the ‘one country, two systems’ proposal seems highly unlikely. Furthermore, the United States assumes a pivotal role in cross-strait geopolitics, intricately tangling the question of Taiwan into the broader scheme of great power politics. This thesis examines the intricate dynamics of the Taiwan issue by analyzing the practical geopolitical reasoning of the PRC intellectuals of statecraft over Taiwan. The theoretical and methodological foundations of this study draw from critical geopolitics and critical discourse analysis. The primary empirical research materials comprise the three Taiwan white papers published by the PRC. In addition, the analysis is supplemented by other official documents as well as vast array of research literature published on cross-strait geopolitics. Building upon Ó Tuathail’s theorization of practical geopolitical reasoning, the paper presents the ‘grammar of geopolitics’ of the Taiwan issue from the perspective of the PRC. Within this analytical framework, three guiding geopolitical storylines were identified: 1) Historical Sovereignty, 2) National Unity under ‘Chineseness’, and 3) Separatism and External Powers as Antagonist Forces. The results reveals that the CCP has constructed the imperative of reunification as an historically and geographically bound inevitability. Nevertheless, China's increasing geopolitical anxiety over achieving the objective of reunification with Taiwan is evidential in its discourses. This increasing geopolitical anxiety is likely to compel the CCP to adopt more coercive actions in the near and mid-term future if it deems it necessary. Given the developments in Taiwan, Sino-U.S. relations and domestically in China, it seems probable that pressure on Taiwan will continue to mount throughout the 2020s. Much of the strategic calculations and geopolitical discourses constructed regarding the Taiwan issue can be attributed to the CCP's concerns about its own legitimacy to rule. Within its geopolitical discourses, the issue of reunification is rendered to an existential question for China and arguably it constitutes a significant part of the modern CCP’s raison d'être. China’s increasing self-confidence as a superpower is continually trembling the dynamics of international affairs and the geopolitical landscape, particularly within the Indo-Pacific region. Consequently, the project of Chinese geopolitics remains an unfinished business, and warrants further contributions from researchers in the field of critical geopolitics.
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(2024)The matter in neutron stars exist under extreme conditions, and the cores of these stars harbour densities unreachable in any laboratory setting. Therefore, this unique environment provides an exceptional opportunity to investigate high-density matter, described by the theory of Quantum Chromodynamics (QCD). This thesis centers on the exploration of twin stars, hypothetical compact objects that extend beyond the neutron star sequence. Originating from a first-order phase transition between hadronic matter and quark matter, our focus is on understanding the constraints on these phase transitions and their effect on the observable properties of twin stars. In our investigation of twin stars, we construct a large ensemble of possible equations of state featuring a strong first-order phase transition. We approximate the low- and high-density regions with polytropic form and connect them to chiral effective field theory results at nuclear densities and extrapolated perturbative QCD at high densities. The resulting equations of state are then subjected to astrophysical constraints obtained from high-mass pulsars and gravitational wave detections to verify their compatibility with observations. Within our simple study, we identify two distinct types of twin stars, each providing a clear signature in macroscopic observables. These solutions originate from separate regions in the parameter space, with both regions being relatively small. Twin stars in our approach generally obtain small maximum masses, while the part of the sequence corresponding to neutron stars extends to large radii, indicating that these solutions only marginally pass the astrophysical constraints. Finally, we find that all twin stars obtain sizable cores of quark matter.
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(2024)Despite the continuous efforts to unveil the true nature of Dark Matter (DM), it still remains as a mystery. In this thesis we propose one model that can produce the correct relic abundance of DM in the current Universe, while fitting into the existing experimentally obtained constraints. In this model we add a singlet fermion, which is a not completely sterile right-handed neutrino, and a heavy real scalar singlet into the Standard Model of Particle Physics (SM) and carry out the relic density calculations. The DM candidate here is the singlet fermion, which acts as a thermally decoupled Weakly Interacting Massive Particle. Theoretical framework is laid out in detail. Special attention is given to obtaining the definition for relic abundance from Lee-Weinberg equation in terms of yield, and the decoupling temperature. It is found, that the usual way of handling the thermally averaged cross section appearing in these definitions is not suitable in this case. In fact, the usual approximations can only be done when thermally averaged cross section is almost linear in $s$, and this is a demand that very few models can satisfy. The correct way to treat the cross section by taking the expansion in terms of the relative velocity is presented with careful attention to detail. This methodology is then applied to the extension of the SM we introduced. Only tree-level processes are being considered. Cross sections are calculated for each possible process to obtain the total cross section needed for the DM relic density calculations. We present how the different free parameters in the theory affect the relic abundance and what masses are allowed for the right-handed neutrino to obtain. It is found out that the parameters in this model are heavily constrained. Yet the model is able to fit into the constraints obtained from branching ratio and direct detection (DD) experiments, while producing the correct relic density. This is true when the mixing angle $\theta$ is of the order $1 \times 10^{-4}$, and right-handed neutrino has the mass of exactly half of the mass of the heavy scalar or higher than the mass of the heavy scalar. It is proposed that allowing lepton mixing and adding a separate mass term for fermion in the model could make the model less restricted. Investigating this would be interesting thing to do in the future. However, the proposed DM candidate remains viable and the upcoming DD experiments will relatively soon reveal if the singlet fermion is the DM particle we are seeking.
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(2024)A quantum computer is a new kind of computer which utilizes quantum phenomena in computing. This machine has the potential to solve specific tasks faster than the most powerful supercomputers and therefore has potential real-life applications across various sectors of society. One promising approach to realize a quantum computer is to store information in superconducting qubits, which are artificial two-level quantum systems made from superconducting electrical circuits. Extremely precise control of these qubits is essential but also challenging due to the excitations out of the two lowest energy states of the quantum system that constitute the computational subspace. In this thesis, we propose a new way to control a superconducting multimode qubit using the unimon qubit as an example. By coupling differently to the different modes of the multimode qubit circuit, we cancel the transition from the first excited state to the second excited state, which is typically the main transition causing a leakage out of the computational subspace. We present a theoretical description of this model by utilizing methods of circuit quantum electrodynamics to compute the energy spectrum and the transition matrix elements of the qubit. By using these results, we simulate the dynamics of the driven unimon qubit undergoing as a single-qubit gate. The result of the simulation shows that this method decreases the leakage relative to the conventional method of driving a qubit, where only one external drive is applied. However, by improving the conventional method with a more advanced pulse optimization method, the leakage becomes smaller than in the standard case of two drive fields. In addition, we find that the practical implementation of our method may be sensitive to variations in the qubit parameters. Therefore, the practical implementation of the method needs further research in the future. By cancelling one energy-level transition of the qubit, we find that other transitions in modes of similar frequency were strongly suppressed. Therefore, this method might be potentially utilized in other qubit operations than the quantum gates, such as in the qubit resetting process, where driving to higher frequency modes of the unimon is preferred.
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(2024)Kaupunkien kasvu, energian kulutuksen lisääntyminen sekä uusiutuvan energian murros ovat aikaansaaneet tuulivoimahankkeiden nopean lisääntymisen Suomessa. Tämän seurauksena tuulivoimahankkeet sijoittuvat entistä syrjäisemmille alueille, jolloin ne ovat merkittävä osa planetaarista urbanisaatiota sekä sen yhtä vaihetta, laajentunutta urbanisaatiota. Planetaarinen urbanisaatio tarkoittaa urbaanin verkoston levittäytymistä kaikkialle yli hallinnollisten tai maantieteellisten rajojen. Laajentunut urbanisaatio taas ilmenee kaupunkikeskusten ulkopuolisille alueille kohdistuvina suurina infrastruktuuri-, teollisuus- ja kehityshankkeina, jotka tukevat keskusten toimintoja ja kasvua. Näin ollen laajentunut urbanisaatio on osa planetaarisen urbanisaation kaikkialle ulottuvaa verkostoa: energia virtaa kaupunkikeskuksista poispäin investointien ja työvoiman muodossa ja jälleen takaisin keskuksiin muun muassa sähkönä ja taloudellisena tuottona. Tutkielmassa perehdytään laajentuneen urbanisaation ilmenemiseen Vaara-Kainuussa tuulivoimaa vastustavien kommenttien kautta. Tutkielman tavoitteena on tunnistaa tuulivoimaa vastustavista kommenteista yhteys laajentuneen urbanisaation teoriaan sisällönanalyysin teemoittelun avulla. Lisäksi tavoitteena on ymmärtää millä tavoin laajentunut urbanisaatio ilmenee tuulivoiman yhteydessä tutkimusalueella. Analyysissä tunnistetaan Vaara-Kainuuseen suunnitellun tuulivoiman rooli laajentuneen urbanisaation prosessissa. Lisäksi tutkielman keskeisenä tuloksena havaitaan laajentuneen urbanisaation ajallinen monikerroksellisuus sekä urbanisaation jatkuva muutos alueella. Tuulivoiman saapuminen Vaara-Kainuuseen muuttaa ja vahvistaa alueella jo ennestään muun muassa luontomatkailun muodossa lymyillyttä laajentuneen urbanisaation verkostoa. Näin ollen tuulivoima, yhtenä laajentuneen urbanisaation kerroksena, vahvistaa energian virtaamista planetaarisen urbanisaation verkostossa ja yhdistää alueen entistä tiiviimmin tukemaan kaupunkikeskusten kasvua.
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(2024)Kaupunkipuilla on valtava merkitys ekosysteemipalveluiden tuottajina kaupungeissa. Julkisilla paikoilla kasvavat puut ovat kuntien ja kaupunkien omaisuutta, jonka hallintaan käytetään puurekistereitä. Puurekisteiden avulla puuomaisuutta voidaan hoitaa pitkäjänteisesti ja suunnitelmallisesti taaten hyvinvoivan puuston myös tulevaisuudessa. Kansalaistiede on kansalaisten aktiivista osallistumista tieteen prosesseihin, kuten tutkimusaineiston keruuseen ja analysointiin. Luonnontieteissä kansalaistieteen käyttö on yleistynyt, kun älylaitteet ovat mahdollistaneet helpon tiedonjaon kansalaistieteilijöiden ja tutkijoiden välillä. Tämän tutkimuksen tavoitteena oli arvioida kansalaistieteen käyttöä kaupunkipuiden kartoitukseen puurekisteriaineiston keräämistä varten ja selvittää, pystyvätkö vapaaehtoiset kansalaiset tuottamaan tarpeeksi laadukasta kartoitusaineistoa puurekistereihin. Tutkimuksessa osallistettiin kahta vapaaehtoisryhmää, koululaisia ja kesätyöntekijöitä, puiden kartoitukseen rakennetuilla viheralueilla. Kartoituksessa määritettiin puiden sijainti, laji ja rungon halkaisijan paksuus. Vapaaehtoisten suoriutumista arvioitiin vertaamalla vapaaehtoisten puista keräämiä tietoja asiantuntijan samoista puista keräämiin tietoihin. Vapaaehtoisten kartoittamista puuhavainnoista hylättiin 67 %. Hylätyissä havainnoissa havainnon koordinaatit oli virheellisesti asetettu puuttomaan paikkaan, monen puun lähimaastoon tai paikkaan, jossa oli tiheästi puita ja suuri latvuspeittävyys, jolloin ei voitu varmasti sanoa, mitä puuta havainto koski. Vapaaehtoiset onnistuivat puiden lajinmäärityksessä hyvin etenkin kasvisuvun tasolla. Vapaaehtoisryhmien mittaamat rungon halkaisijat erosivat asiantuntijamittauksista yksirunkoisilla puilla. Kaikista vapaaehtoisten mittaamista rungon halkaisijoista 77 % mitattiin onnistuneesti ±2,54 cm:n virhemarginaalin sisään asiantuntijan mittaustuloksesta. Rungon halkaisijan mittaamisessa ja puiden lajinmäärityksessä kansalaistieteilijöiden keräämän tiedon laatu oli pääasiassa riittävä kuntien ja kaupunkien puurekisterien käyttötarkoituksiin. Tutkimuksessa käytetty ilmakuviin perustuva puun koordinaattien merkitseminen toimi vain katualueilla ja muilla harvapuustoisilla alueilla. Puurekisterin tietojen keräysmenetelmää valitessa on tärkeää miettiä, mihin ja kuinka tarkkaa tietoa puista tarvitaan. Vapaaehtoisten työpanosta voisi yhdistää muilla menetelmillä saatuihin sijaintitietoihin tai käyttää puihin liittyvien lisätietojen hankinnassa.
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(2024)Tree microhabitats are important in assessing forest biodiversity and ecological value. Knowledge of what types of forests and trees bear the most microhabitats can be useful in sustainable forest management and conservation. Based on research that has been done on assessing the main drivers of microhabitats, tree age, size and developmental stage have been established as the main driving factors for microhabitats. Terrestrial laser scanning data has been used in microhabitat modelling, either at forest stand scale, or by directly detecting certain microhabitats from the data using machine learning. However, high precision individual tree level architectural data facilitated by terrestrial laser scanning and quantitative structure modelling has not yet been tested in microhabitat related research. In this thesis I use the detailed tree-level information that the quantitative structure models provide to determine whether high precision tree architectural data improves the modelling performance of tree microhabitats. Terrestrial laser scanning data was collected from ten plots in a hardwood riparian forest area near Leipzig, Germany. Two tree microhabitat inventories from these ten plots collected in the winter of 2020-2021 and January 2023 respectively as reference data sets. Running increasingly complex models for predicting microhabitat richness for the two datasets I found that 1) While the performance gets better with addition of more tree structural variables, the difference was not substantial between models using only variables attainable by less labour-intensive methods and models with more complex, TLS-derived variables. 2) Comparing the performance metrics between the two datasets showed that the models performed very differently between the inventories, suggesting that microhabitat inventory data collection is susceptible to subjectivity, and the surveys are prone to having observer biases. These discrepancies between the datasets further reinforce the established consensus that tree microhabitats are hard to detect. Difficulties with creating reliable reference data sets, along with the inherently random nature of tree microhabitat occurrence can make microhabitat modelling difficult. This thesis concludes that high precision tree structural data might not increase the microhabitat prediction power in a way that justifies the cost. The results support the established consensus that microhabitat occurrence is mainly driven by tree size and living status. Variables such as species, tree neighbourhood metrics and stand level metrics were not included in this study, but should be researched more, as for example, tree structural characteristics and compartmentalization capacity vary between tree species. Additionally, based on the findings in this thesis, further effort into the standardisation of microhabitat inventories and their collection should be done. There should be little to no room for interpretation regarding the typologies of microhabitats and their related field work methodologies, leading to less observer biases and more comparable and comprehensive data.
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(2024)Satellite positioning is vulnerable to interference due to the power of satellite signals. Satellite signals are exceptionally weak when they arrive to the Earth and therefore susceptible to radio frequency interference (RFI). This makes even low-power interference effective, possibly for radius of several kilometers. Global Navigation Satellite System (GNSS) services, such as positioning, navigation and timing services (PNT), are widely used among our society by civilians and authorities. Critical infrastructures, such as money transfer and electricity transmission networks, rely on accurate timing data provided by GNSS’s atomic clocks. These services are under a serious threat by RFI —intentionally created or not. In the areas that GNSS jamming signal can cover, the PNT services are most likely degraded or entirely unavailable. The easiest way to intentionally create RFI is to create jamming interference by broadcasting empty signal on satellite signal frequency with simple jamming radio devices aka jammers. Jammers disturb GNSS services by blocking entire positioning data or deteriorating positioning accuracy which leads to inaccurate location information. Jamming is an emerging global threat for GNSS services since jammers can be easily bought online, even though jamming is illegal in Europe and many other regions. Incentives for jamming differ by the user group of jamming equipment. Civilian jamming is mostly done with low-power jammers for protecting privacy by hiding location information and it is normally done without further knowledge about the effects for the surrounding environment. The more severe threat is done with high-power jamming equipment by professionals. This kind of interference has motives for either disturbance or denial of GNSS services or to defend against different location-based measures. Jamming and RFI are significant parts of electronic warfare. This study tested the usability of MATLAB’s RF Toolbox on simulating jamming signals horizontally in different topographies across Finland to demonstrate how spatially effective jamming actually is. Used jamming signals were simulated with four different powers on Galileo’s E1 and GPS’s L1 signal (1575.42 MHz) to exemplify the effects of different power interference. The simulations and inspection of signal propagation were done with MATLAB by visualizing the expected power of jamming signal and calculating propagation loss for receiver matrix above digital elevation model (DEM). The used method was not able to calculate propagation values for varying power and exact values for signal attenuation of jamming signal cannot be calculated with MATLAB. RFI is illegal in Finland, therefore field work is not possible for this kind of study. This study highlights the hindering or blocking effect of topography on jamming signal propagation alongside with the effectiveness of different jammer power levels. Signals obey signal propagation models, but topographic characteristics, such as hills, have an ability to hinder the propagation. The results emphasize the spatial effects of even low-power jammers that are used by civilians and accentuates the significance of topography to signal propagation. Effective jamming over different topographic characteristics can be conducted with even 500 mW jammer and increase of jammer power is able to cover extensive areas of irregular terrain. The most vulnerable areas to GNSS jamming are open, unbuilt areas. However, the impact of locally bounded urban jamming scenario is also severe to the population and infrastructures of the area.
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