Browsing by Title

Työssä tarkastellaan majoriteettikvanttorien ilmaisuvoimaa sanamallien kontekstissa. Kuten eksistenssikvanttori (∃) ja universaalikvanttori (∀), majoriteettikvanttori on looginen kvanttori. Sillä voidaan ilmaista väitteen pätevän yli puolelle tarkasteltavan mallin perusjoukon alkioista. Deskriptiivisen vaativuusteorian näkökulmasta uniformi TC⁰-piirivaativuusluokka vastaa ensimmäisen kertaluvun logiikkaa yhteenlaskulla, kertolaskulla ja majoriteettikvanttorilla varustettuna. Työssä tutkitaan TC⁰-luokan sisäistä rakennetta rajoittamalla tarkastelu loogiseen fragmenttiin, jossa käyttettävissä on vain majoriteettikvanttori ja järjestysrelaatio. Työssä osoitetaan, että sekä eksistenssi- että universaalikvanttoria voidaan simuloida majoriteettikvanttorin ja järjestysrelaation avulla. Myös yhteenlasku ja perusjoukon parillisuus ovat ilmaistavissa. Sen sijaan kertolasku ei ole ilmastavissa yksipaikkaisella majoriteettikvanttorilla. Lisäksi työssä osoitetaan, että kertolasku voidaan ilmaista kaksipaikkaisella majoriteettikvanttorilla. Tästä seuraa, että kaksipaikkainen majoriteettikvanttori on aidosti voimakkaampi kuin yksipaikkainen majoriteettikvanttori.

Power ultrasound increases production efficiency in the industry, and therefore reduces emissions. This advantage arises from the ability of ultrasound to mitigate fouling. Ultrasound solution requires clamping the transducers onto the external wall of the production equipment, typically made of steel. A challenge then arises, since mechanical loading by the wall hampers the natural resonating of the ultrasonic transducer and therefore reduces power transmission. To overcome this limitation, airgap contact coupling (ACC) is proposed. ACC features an airgap to reduce the mechanical loading and two protruding elements for mechanical contacting and sound delivery. Finite-element method (FEM) simulations are employed to evaluate the physical mechanisms behind ACC. For the comparison, direct traditional contact coupling (TCC) is evaluated. To assess the acoustic power delivery by ACC and TCC, calorimetric measurements were used. A water-filled stainless-steel pipe with a 2 mm thick wall and 136 mm outer diameter was sonicated. To prevent heat transmission to ambient air, it was covered by isolating foam. ACC and TCC were sonicated at their coupled resonance frequencies, respectively at 19.2 kHz and 28.1 kHz. A power delivery ratio was determined by the calorimetric power against the sonication power. ACC resulted in a power delivery ratio of 27.4±6.3 % whereas that for TCC was 6.1±0.6 %. ACC was thereby shown to transmit 6 dB more acoustic power than TCC. In conclusion, a novel contact coupling method is proposed for industrial metal-walled equipment. The proposed new approach enhances the utility of power ultrasound for online cleaning and prevention.

Coxeterin ryhmät ovat ryhmiä, joille voidaan antaa esitys G=<s_1, ... s_d: s2_i=1, (s_i s_j)^m_{ij}=1> missä m_{ij}ЄZ. Tämän pro gradun tehtävänä on näyttää, että kyseisen rajoitetun esityksen ryhmiä on rajallinen määrä sekä esittää niiden luokittelu. Luokitteluun tarvittavia työkaluja ovat Coxeterin graafit ja matriisit. Pro gradussa muistutetaan tarpeellisista lineaarialgebran määritelmistä sekä annetaan taustatietoa positiividefiniitti ja positiivisemidefiniitti matriiseista. Lisäksi käydään läpi ryhmäteorian taustoja ja erityisesti ryhmien esittämistä generaattoreiden ja relaatioiden avulla. Taustatietojen jälkeen määritellään Coxeterin graafit muutamien esimerkkien kera ja selitetään miten matriisi voidaan johtaa Coxeterin graafin esityksestä. Työssä näytetään, että kaikki listatut Coxeterin graafit ovat joko positiividefiniittejä tai positiivisemidefiniittejä sekä todistetaan, että ne ovat ainoat positiividefiniitti ja -semidefiniitti graafit. Luokittelu loppuu siihen. Lopuksi pro gradussa annetaan yleisempi kuvaus rajallisten heijastusten ryhmistä (finite reflection groups).

Electrical breakdowns occasionally occur near the first walls of fusion reactor chambers and the accelerating cavities of linear colliders, such as CLIC. These arcing events are localised plasma discharges, which are formed under high voltage electrical fields. Vacuum arcs cause various surface damage on the fusion reactor and linear accelerator structures. The surface damage, most significantly craters, have been studied experimentally, but the mechanism of the formation of this damage is still not clear. In this thesis we use the large-scale molecular dynamics simulations to study crater formation on Cu surface. We used ion irradiation to model the arcing events, where plasma ions are accelerated via the shield potential towards the metal surface. This ion irradiation causes multiple overlapping cascades in Cu surface, what can lead to the crater formation. The main goal was to be able to produce surface damage, which is identical to experimental results. Our results are divided to three categories. First we examined which are initial conditions needed to form experimental like craters. The electric field emission current accompanying the plasma discharge process, most likely, is to heat the sample locally to very high temperatures. Therefore we tested molten and solid structures at different temperatures, as well as different scenarios of cooling of the sample via electronic heat conduction. Second, we examined how different variables, such as the fluence of the ions, the energy flux or the potential model, affect on the crater shape. These results were compared with the experimental crater profiles in order to find out reasonable values. We also analysed how the volume of the produced crater depends on fluence. Our third part of investigation was not actually concentrated on the surface damage, but on dislocations and other damage under the surface. We again studied how different parameters affect on the results. We compared the simulations by calculating the number and ratio of non-FCC atoms in the bulk. The fluence dependency of the defects was studied as well.

This thesis examines designing and implementing adaptive visual cues for a social virtual reality meditation environment. The system described here adapts into user’s bio- and neurofeedback and uses that data in visual cues to convey information of physiological and affective states during meditation exercises supporting two simultaneous users. The thesis shows the development process of different kinds of visual cues and attempts to pinpoint best practices, design principles and pitfalls regarding the visual cue development in this context. Also examined are the questions regarding criteria for selecting correct visual cues and how to convey information of biophysical synchronization between users. The visual cues examined here are created especially for a virtual reality environment which differs as a platform from traditional two dimensional content such as user interfaces on a computer display. Points of interests are how to embody the visual cues into the virtual reality environment so that the user experience remains immersive and the visual cues convey information correctly and in an intuitive manner.

Topological defects and solitons are nontrivial topological structures that can manifest as robust, nontrivial configurations of a physical field, and appear in many branches of physics, including condensed matter physics, quantum computing, and particle physics. A fruitful testbed for experimenting with these fascinating structures is provided by dilute Bose–Einstein condensates. Bose–Einstein condensation was first predicted in 1925, and Bose–Einstein condensation was finally achieved in a dilute atomic gas for the first time in 1995 in a breakthrough experiment. Since then, the study of Bose–Einstein condensates has expanded to the study of a variety of nontrivial topological structures in condensates of various atomic species. Bose–Einstein condensates with internal spin degrees of freedom may accommodate an especially rich variety of topological structures. Spinor condensates realized in optically trapped ultracold alkali atom gases can be conveniently controlled by external fields and afford an accurate mean-field description. In this thesis, we study the creation and evolution of a monopole-antimonopole pair in such a spin-1 Bose–Einstein condensate by numerically solving the Gross–Pitaevskii equation. The creation of Dirac monopole-antimonopole pairs in a spin-1 Bose–Einstein condensate was numerically demonstrated and a method for their creation was proposed in an earlier study. Our numerical results demonstrate that the proposed creation method can be used to create a pair of isolated monopoles with opposite topological charges in a spin-1 Bose–Einstein condensate. We found that the monopole-antimonopole pair created in the polar phase of the spin-1 condensate is unstable against decay into a pair of Alice rings with oscillating radii. As a result of a rapid polar-to-ferromagnetic transition, these Alice rings were observed to decay by expanding on a short timescale.

Creep is time dependent plastic malformation of solids, that happen in static stress and temperature when threshold values are met. Creep occurs at high temperature, meaning temperature more than 30% of material's absolute melting temperature (this limit is a little lower with plastics, and higher in ceramics). The malformations it causes can lead to rupture, which usually happen in a short time compared to the duration of the whole process. The creep effect itself is known from already the 19th century, and for metals it's quite clear that diffusion is always present in creep (Coble and Nabarro-Herring creep), and that dislocations can increase the rate of creep strain. Effects of creep can be seen e.g. in power plants and engines, where turbine blades, turbines, pipes and vessels are all the time at high temperature and stress. Also creep relaxation is often 'loosening' bolts which needs to be retightened. In regular office creep can be seen in paper clips, especially in plastic ones, which relax and lose grip fast because of the low melting point of plastics. Creep, because it usually needs long time to be visible, has been part of accidents, too, e.g. in '9/11'. Creep appears in 3 stages (primary (transient), secondary (steady-state), tertiary), and depending on the application, either secondary or tertiary is the most important one. The secondary creep is important for displacement-, buckling- and relaxation-limited situations, and tertiary for the rupture-limited ones.

The Baltic Sea is a popular cruising area during the summer months (April till September) with international cruise lines. During these months cruising ports of the Baltic Sea handle the cruise ship generated waste. As the cruising business has been rapidly growing the waste streams has become larger. Present laws and regulations prevent most discharges into the Baltic sea. According to these regulations a ship has to discharge all waste at the port of call produced on board since last port of call. Thus, ports have different waste management strengths and weaknesses. Therefore, it is here argued that an updated collaboration among the ports where individual ports would be specialized in specific types of waste handlings ought to benefit the environmental work of the port and the cruise lines and thus also the environment. The thesis will through experts' ideas and opinions from each port study whether an updated waste management can be introduced in the ports of the study. The individual ports are Port of Helsinki, Port of Tallinn, Ports of Stockholm and Copenhagen Malmö Port. Cruise ship generated waste has been study to some extent around the world, but there are only a few studies in the Baltic Sea area. Secondary data and semi structured thematic professional interviews was used to find answers on the research questions. Secondary data in form of waste streams quantities from cruise ships 2010–2014 in the ports of the study was gathered. The gathered data enabled comparisons among the ports and shows in what way the fractions are divided among them. The interviews were held at each port with one to three participants at the time. In total 12 persons were interviewed at nine occasions. The transcribed material was analysed through thematising. The research shows cruise ship generated waste fractions are unevenly distributed among the ports in the Baltic Sea. Hence, this also means the ports are already specialized in receiving special types of waste fractions. The ports are receiving sorted waste and different fractions are being handled. The ports have a close cooperation regarding cruise ships but the study shows the ports are open for new sustainable solutions. This thesis opens up the discussion on cruise ship generated waste in the Baltic Sea. The study shows there is little research done on this matter and further studies are needed. The waste management of all parties involved are important in order to act environmentally friendly and harm the surrounding areas the least. This research provides the Baltic Sea cruising ports with one possible solution on an updated waste handling management in the area.

Africa has recently increased its share of the global market, and the continent’s potential has been recognized globally. The continent has experienced a lot of oppression and forced changes in history, and it is currently developing its new identity with relatively young states and its fast-growing population. African Union (AU) is calling pan-African ideology to bring together the African people in their blueprint and master plan Agenda 2063, where the cultural heritage is at the core. Culture is also at the core of the creative economy, and the creative economy's share of the global economy is growing. Due to globalization and digitalization, the knowledge from other cultures is spreading rapidly, which is the basis of a cultural shift both at local and global levels. This research investigated the culture and the creative economy as builders of society in Kenya. Kenya has been very successful in the field of Information and Communications Technology (ICT), the state takes its cultural heritage seriously in its development programs and their focus is especially on the potential of the youth in the creative economy. Kenya has a vast cultural diversity in the state with its officially recognized 44 tribes. This cultural diversity plays a significant role in the creative economy. According to the United Nations Conference on Trade and Development (UNCTAD, 2020), the creative economy has no single meaning, as the concept is constantly evolving. The basic elements of the concept are from human creativity, ideas, and intellectual property, knowledge and technology. The creative industries include such as music, film, video, arts and crafts and performing arts. These elements are the basis of the creative economy, in addition, they have a significant commercial and cultural value. The research was conducted in Kenya during January and February 2021, and the data was collected from two main geographical research areas, the city of Nairobi and Taita-Taveta County. The geographical research areas were chosen by their cultural diversity, the creative economy and their urban and rural statuses. Nairobi has a classification of a creative city where the digital creative economy is booming, and the city is attracting people around East Africa. Taita-Taveta respectively is a rural county near the Kenyan coast, where the creative economy is mainly in the traditional form, for example, crafting and basket making. The research combined the elements from the ethnographical, hermeneutical and critical approaches by using unstructured, structured interviews and observation, as the methods combined qualitative methods with numerical data. The results show that the culture and the creative economy do build the society in Kenya. It is seen in each level of society, for example, among the families, tribes, counties and even the government. Each level influences and controls the way culture and the creative economy build the society in Kenya. The meaning of the community arose in culture and the creative economy shifts, as they provide help in the mitigation and adaptation into new situations. With the exponential population growth, the share of the youth is rising, culture and the creative economy have the potential to provide jobs for the youth in the future. There are challenges with culture and the creative economy in Kenya. First, to preserve the cultural diversity in Kenya among the youth. Second, to target the governmental policies to the right actions and towards the right groups, which would then support the sector itself. Due to attitude shifts, the role of the youth is a significant point to consider. Furthermore, there is a vast gap between the government and the community, which causes a lot of harm to the creative economy, as the policies do not support the creative sector. If these significant points are solved, there is a vast potential for the culture and the creative economy to continue building the society in Kenya.

Cumulonimbus (Cb) clouds form a serious threat to aviation as they can produce severe weather hazards. Therefore, it is important to detect Cb clouds as well as possible. Finnish Meteorological Institute (FMI) provides aeronautical meteorological services in Finland, including METeorological Aerodrome Report (METAR). METAR describes weather at the aerodrome and its vicinity. Significant weather is reported in METARs, and therefore Cb clouds must be included in it. At Helsinki-Vantaa METARs are done manually by human observer. Sometimes Cb detection can be more difficult, for example, when it is dark, and it is also expensive to have human observers working around the clock all year round. Therefore, automation of Cb detection is a topical matter. FMI is applying an algorithm that uses weather radar observations to detect Cb clouds. This thesis studies how well the algorithm can detect Cb clouds compared to manual observations. The dataset used in this thesis contains summer months (June, July and August) from 2016 to 2020. Various verification scores can be calculated to analyse the results. In addition, daytime and night-time differences are calculated as well as different years and months are compared together. The results show that the algorithm is not adequate to replace human observers at Helsinki-Vantaa. However, the algorithm could be improved, for instance, by adding satellite observations to improve detection accuracy.