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Analysis and Simulations of Hybrid Circuit Breaker Technologies in Multi-Terminal HVDC Networks
Full text linkIt is established that voltage source converters (VSC) are required for multiterminal operation of a HVDC network. This converter technology is vulnerable to DC side faults, and it is crucial for a fast interruption to avoid its freewheeling diodes to have a breakdown. Several circuit breakers have been investigated to find the best one for multi-terminal operation. It is found that the fastest circuit breaker, with a reasonable on-state loss, is the hybrid circuit breaker. Two circuit breaker models are tested, active hybrid circuit breaker with 1 % on-state losses, and passive hybrid circuit breaker with 0.001 % on-state losses. They are compared to check how the interruption time will affect the system, and the requirements of the circuit breaker.
For a multi-terminal operation, it is important with a proper detection algorithm. The algorithm allows for a proper detection of the fault and where it has occurred. This is important for a seamless operation of the multi-terminal network. It is found that the derivative of the current is a good detection algorithm, as it is quite simple and works properly. A fault that occurs close to the converter in a symmetrical system is difficult to handle for the circuit breakers detection algorithm. This is due to the similar magnitude of the derivative that may occur on the circuit breakers in the adjacent cables.
When the faulty cable is isolated, the power flow will change direction through the adjacent cable. This gives a seamless operation of the multi-terminal network. It is found that the faulty cable can be isolated within 3 ms, using the active hybrid circuit breaker
Signatures of the Transition between Topologically and Magnetically Ordered Ground States in the Schwinger-Boson Mean Field Theory of Frustrated Quantum Antiferromagnets - An analysis of the triangular lattice Heisenberg model with nearest and next nearest neighbour interactions
Full text linkWe present three different methods of finding the critical spin value of the quantum phase transition between the spin liquid and the Néel order phase on the mean field triangular Heisenberg antiferromagnet at K. These methods are: using the sublattice magnetization as an order parameter, looking at the scaling of the energy difference of topologically degenerate states in different phases, and the quantum fidelity approach. All of these methods are able to pick up the signal of the phase transition, and their estimated numerical values of agree for systems where the relative strength of next nearest neighbour interaction compared to the nearest neighbour interaction is small. For the relative interaction strength and , all three methods predict and respectively, while gives deviating results. This deviation might be caused by the influence of other magnetically ordered states that we have not accounted for in our calculations, and so we restrict the validity of our results to
A holistic model for analyzing energy benefits of urban density by relating energy use, building height, and overall city structure
No full textMore than half of the world population live in cities, and the urban population is further expected to almost double within 2050. This opens a rare window of time for realizing energy savings through overall city planning. How the overall city structure influence energy consumption is, however, still poorly understood. A central theme in the sustainable development of urban form is the compact city, and as a key instrument of this densification, tall buildings may prove important. Yet, the overall energy-saving potential of building taller and denser remain largely unclear. Moreover, current studies are described as far from holistic, not capturing the interconnectedness and complexity of the system as a whole. They are mostly qualitative, and methods depend largely on context. There is thus a lack of a clear theoretical framework for understanding energy consumption at the urban scale. The ambition of this thesis is to address this knowledge gap.
This thesis develops a holistic optimization model for investigating the extent to which urban density and urban structure influence the energy consumption of the urban system. Energy aspects in land use planning, including the influence of building height, are addressed. The model relates energy costs of building heights of three stories and greater, with transportation and infrastructure energy benefits of building denser. Multiple scenarios of differing climate, population, and other variables have been simulated. Only factors considered to be correlated with urban density are taken into account. Of these, solar irradiation and the urban heat island effect have been left out due to their complex nature.
A denser and taller city structure than what is normal in cities today is found to be optimal for low urban energy use. The most influential urban density indicators are embodied energy (most heavily influenced by building lifetime) and floor area per capita. The findings of the research indicate that building heights approximately in the range 7-27 stories are optimal for a given population and building lifetime. For buildings taller than this the increased embodied energy outweighs further reduction potentials of other elements. Energy use per capita in a city with optimal density is increasing slightly with population. Transportation energy is found to be much less important than building energy, especially in dense small area scenarios, but becomes increasingly important for low-density scenarios with large urban areas. Road construction, elevator energy, and vertical water transportation energy does not significantly affect the overall energy budget. An energy saving potential for the urban metabolism of the investigated elements of approximately one-third compared to a low-density scenario is found to be viable. However, energy savings of further densification in areas that already have high-density, close to the optimal, are not significant. The energy expenditure is significantly lower in the dense and tall scenarios - with implications for current and near-future city planning policies on optimizing land use based on city size. These findings improve the basis on which decisions are made for policy-makers and urban planners worldwide, although the significance of solar irradiation and the urban heat island effect should be investigated further. The model is a generalized theoretical abstraction and thus has its limitations. Further development of the model by including more elements as well as reducing uncertainties is needed. Nevertheless, the findings are relevant both for further development of existing cities and for conceptually planned future cities
pH-dependence of chloride binding in ordinary Portland cement
Full text linkA new method for artificially leaching hydrated cement paste and studying how lowered pH in the pore solution affects chloride binding has been developed. Hydrated cement paste was exposed to a NaCl-solution before being acidified by adding small volumes of HCl in steps over several days, gradually lowering the pH. A pH-development curve was established, determining how the pH in the pore solution responded to increasing amounts of acid being added. The chloride binding of the cement paste as a function of the pH and free chloride concentration was then determined. For the range of pH from 12 to 13, decreasing pH increased chloride binding. At a pH of 11, the cement paste showed almost no chloride binding. The mechanisms of changes in chloride binding were investigated using TGA, XRD, SEM-EDS, ICP-MS and thermodynamic modelling. One of the main chloride binding phases, Friedel s salt, could not be detected with the applied techniques due to the cement paste being cured at 60 °C, therefore its influence could not be verified. Thermodynamic modelling does however confirm the possibility of Friedel s salt decomposing at pH 11. The increase in chloride binding from pH 13 to 12 is most likely related to the changes in the main hydrate phase C-S-H. The effect of pH on chloride binding should be accounted for in service life prediction models for concrete structures exposed to chlorides
Proposed Access to Future Mining Operations in the Rupsi, Giken and Charlotta Ore Deposits in Sulitjelma - Including a Suggestion for an Exploration Drilling Campaign to Investigate the Rupsi Ore Body
No full textNye Sulitjelma Gruver AS planlegger ny drift i Nordgruvefeltet i Sulitjelma, nærmere bestemt på den hittil uberørte Rupsi-forekomsten, på bunnen av Nedre Charlotta gruve og på forlengelsen av Giken-forekomsten. Til dette kreves en adkomststoll og en nedadgående rampe. Parallelt med driving av adkomststollen er det også tiltenkt å gjennomføre undersøkelsesboring på Rupsi-forekomsten. De allerede utdrevne gruverommene vil kunne påvirke stabiliteten til en fremtidig rampe, og det er derfor viktig at denne plasseres i en tilstrekkelig sikker avstand fra disse. I tillegg er det blitt lokalisert en klorittsone i bunnen av Rupsi-stollen som kan være av stabilitetsmessig betydning for en fremtidig adkomststoll.
Det er på grunnlag av tilgjengelig geologisk informasjon fra området blitt gjort en vurdering av bergarter i området. En terrenganalyse er blitt gjennomført i ArcGIS 10.2 for å identifisere svakhetssoner og andre strukturer som kan være av betydning for den planlagte traséen. Gruvekart og geologiske vertikalprofil fra det aktuelle området er blitt samlet inn og digitalisert for etablering av en forenklet 3D-modell av gruverommene og Rupsi-forekomsten i Leapfrog Geo. Tre profiler av det aktuelle området er blitt gjenstand for numerisk analyse i Examine2D for kalkulering av sikkerhetsfaktoren rundt gruverommene Nedre Charlotta og Giken og den planlagte adkomststollen. Som følge av usikkerheten til inngangsparameterne er det blitt foretatt parameterstudier av inngangsparameterne enaksial trykkfasthet, σci, og GSI. I 3D-modellen i Leapfrog ble det, basert på resultatene fra den numeriske analysen og bestemmelse av stigningsgrad og horisontal krumningsradius, lagt inn to alternative forslag til adkomststoll, oppboring av Rupsi-forekomsten og videre rampe ned til bunnen av Nedre Charlotta og Giken. De to alternativene ble konstruert med ulike stigningsgrader, en med stigning 1:8 (12,5 %) og den andre med stigning 1:10 (10 %).
De geologiske vertikalprofil tyder på at forekomstene i Nordgruvefeltet fortsetter med samme fall hovedsakelig med kloritt i liggen og skifer i hengen. Fremtidig brytning på bunnen av Nedre Charlotta og forlengelsen av Giken-forekomsten kan dermed gi problemer med skviseberg. Terrenganalysen viser generelt et bruddmønster med strøkretning ØNØ-VSV som kan medføre stabilitetsmessige problemer for en nedadgående rampe med tanke på dens ugunstige orientering i forhold bruddmønsteret. Numerisk analyse indikerer potensielle bruddsoner fra gruverommene Nedre Charlotta og Giken med maksimale utstrekninger opp mot henholdsvis 146 og 215 meter. Den numeriske analysen viser også at det vil forekomme skjærbrudd i veggene til adkomststollen som følge av klorittsonen. Det anbefales å sikre med fiberarmert sprøytbetong og minimum 2,4 meter lange bolter i veggene. Fra skjematisk layout av de alternative forslagene i Leapfrog, kom det frem at alternativ 1 (stigning 1:8) fikk resulterende ortmeter på 6431 og resulterende boremeter på 1241. Alternativ 2 fikk resulterende ortmeter på 7804 og resulterende boremeter på 855.
En grov kostnadsberegning basert på drivekostnader og diamantkjerneboring, tilsier at alternativ 1 har best kostnadseffektivitet med en kostnad på ca. 226 millioner kroner sammenliknet med alternativ 2 sin kostnad på ca. 274 millioner kroner
Participatory design research for urban community building in China
Full text linkThis thesis aims to provide direct input for the deliverables required for Task 1.1 of the TRANS-URBAN-EU-CHINA project. This thesis means to create a knowledge base about how to experiment with context-specific and citizen centered studies and participatory design (PD) approaches, and how to map citizens' needs through insights from theories of social practice and user-centered design in China. With the research questions of 1) what the current status of PD development related to fields that contribute to community building in China is; 2) What the possible challenges and issues to practice PD in the Chinese context, and the possible way to coping are; and 3) What information can be concluded and utilized in future studies, focusing on both what works well, and new insights about what could work in the context that so far are seen as potentially challenging.
Starting with reviewing previous literature relevant to this topic, I identify the challenges of conducting PD research in the Chinese context, including communication, knowledge-transfer, balanced decision-making regime with distinguishing of scale of participation. I also find that PD practices need more focus on ethnographic methods and reward system in the Chinese context. Following the findings of literature review, this thesis is developed further with interviews of six experts who have performed relevant fieldworks in China. Based on the interviews, I conclude that, when conducting research and PD, practitioners and researchers need to cultivate and maintain interpersonal relationships and trust with local participants, and build up effective communication channels and mechanisms for the local Chinese context. This thesis proposed recommendations of a PD framework and tools for PD activities with explained scenarios, indicate different possibilities of improving community-based contextual PD application, and emphasizes the research of PD theories and practice need more focus for the Chinese context in future
Physical activity tracking - Personal activity intelligence (PAI) versus 10000 steps per day and the effects on cardiorespiratory fitness, body composition and blood pressure in inactive overweight and obese
Full text linkIncreased amounts of sedentary time, and less physical activity (PA) have become a global concern, and may result in increased risk of cardiovascular disease (CVD). Thus, it has become an important task to increase PA in the general population. Personal activity intelligence (PAI) is a new metric for activity tracking that takes into account age, sex, resting and maximum heart rate (HR), and give an individualised goal for PA. 100 PAI per week has been found to reduce the risk of CVD and all-cause mortality in epidemiological studies, but the link through increased cardiorespiratory fitness (CRF) has not been established in a controlled clinical trial. The aim of this study was to investigate the effects of following the advice of maintaining 100 PAI per week compared to the effects of walking 10 000 steps daily on CRF, blood pressure (BP) and body composition.
21 obese or overweight men (n=8) and woman (n=13) were randomized to either of two groups; (i) The PAI group (n=10) followed the advice of maintaining a score of 100 PAI for 8 weeks (ii) The step group (n=11) followed the advice of walking 10 000 steps per day. VO2max directly measured with cardiopulmonary exercise testing (CPET), body composition measured with bioelectrical impedance analysis (BIA) and blood pressure (BP), was measured pre- and post-intervention. Analysis of covariance (ANCOVA) was used for comparison between the two groups, and Wilcoxon signed-rank test was used for within group analysis.
Results: No significant differences were found between the two groups.
A negative association between mean weekly PAI and increase in absolute maximum oxygen uptake (VO2max) was found (r = -0.712, p=0.031), and a moderate non-significant positive association was found between mean daily steps and increase in absolute VO2max. A significant median increase (p=0.009) in median VO2max relative to body weight was found in the step group, while a non-significant median increase (p=0.051) was found in the PAI group. The largest mean and absolute increase in VO2max was found in the PAI group. Median BF% was significantly (p=0.028) reduced in the PAI group, and median body weight was significantly (p=0.047) reduced in the step group. No significant change in BP was found within the groups.
Participants in both groups improved PA from pre- to post-intervention. Neither of the groups increased median absolute VO2max significantly, and there was no statistically significant evidence that either of the interventions was superior. The increase in relative VO2max is probably explained by decreased body weight. However, a trend towards a large mean increase in CRF was observed in the PAI group. Future randomized controlled clinical trials may use data obtained in this study for sample size estimations
TURING GAIA - The Making of Behavioral Media: Sensibilities Through Other-Agents
Full text linkEnglish summary
The artistic research project TuringGaia | The Making of Behavioral Media: Sensibilities Through Other-Agents aims to explore how AI-driven Non-Playable Characters (NPCs), or rather agents, within digitally simulated environments, and beyond, can foster and augment human sensibilities. The project presents a multidisciplinary conceptual framework necessary to effectively establish beneficial relationships between humans and nonhuman agents. The foundations of this framework are constructed via questions regarding media, art, narrative, aesthetics and artificial intelligence (AI).
The material expressions of this project are the physical manifestation of those theoretical investigations and have resulted in two physical prototypes: A generative audio-visual installation called TuringGaia | Entering ThermoDome, and an immersive Virtual Reality (VR) installation called TuringGaia | Markov’s Umwelt.
Furthermore, this project extends also as a critical investigation of AI technologies and their implications on digital media and how their pervasive use might distort our cultural landscape in a monoculture. This study investigates an emerging generation of media driven by Large Language Models (LLMs), referred to as Behavioural Media (BM). It explores how BM can further exacerbate cultural homogenization but also how, when properly addressed, BM can present opportunities to foster human sensibilities.Norsk sammendrag
Kunstnerisk forsknings-prosjektet TuringGaia | The Making of Behavioral Media: Sensibilities Through Other-Agents har som mål å utforske hvordan KI-drevne, ikke-spillbare karakterer (NPC-er) – eller kun agenter, i både digitalt simulerte omgivelser og forbi kan fostre og utvide menneskelig sanselighet.
Prosjektet presenterer et flerdisiplinært, konseptuelt rammeverk for å effektivt forhold mellom menneskelige og ikke-menneskelige agenter. Fundamentene for dette rammeverket er konstruert gjennom spørsmål om media, kunst, narrativ, estetikk og kunstig intelligens (KI).
De materielle uttrykksformene til dette prosjektet er de fysiske manifestasjonene av disse teoretiske undersøkelsene og har resultert i to fysiske prototyper: En generativ audio-visuell installasjon kalt TuringGaia | Entering ThermoDome, og en omsluttende Virtual Reality- (VR) installasjon kalt TuringGaia | Markov’s Umwelt.
Videre utvides dette prosjektet også som en kritisk undersøkelse av KI-teknologier og hvilke implikasjoner de har for digital media og hvordan deres inntrengende bruk kan forvrenge vårt kulturelle landskap til en monokultur.
Denne studien undersøker en fremvoksende generasjon av media drevet av store språkmodeller (LLMs), her omtalt som atferdsmedia. Den utforsker hvordan atferdsmedia kan forverre kulturell homogenisering, men også hvordan, dersom korrekt adressert, kan fremstille muligheter til å fremme menneskelig sanslighet
Identification of N2O formation in an ammonia/n-heptane dual-fueled compression ignition engine using numerical simulations
Full text linkAmmonia, as an alternative fuel to reduce harmful gas emissions from internal combustion engines, has gained increased interest during the last decade. However, the combustion of ammonia could lead to increased formation of nitrous oxide (N2O), a potent greenhouse gas that can offset the climate benefits of using a carbon-free fuel. N2O is an intermediate species that ideally gets reduced by thermal decomposition or reacting with atomic hydrogen in the later stage of the combustion, leaving low post-flame concentrations. This study investigates events leading to N2O formation and accumulation in a dual-fuel direct injection compression ignition engine operated with ammonia and diesel. The injection timing of diesel is fixed, while four different injection times of ammonia are investigated. The results reveal that N2O accumulation within the engine cylinder can be traced to phenomena that prevent complete combustion. The findings in this article show accumulation of N2O close to the cylinder walls, in regions cooled by ammonia evaporation featuring elevated ammonia concentrations, and in areas with slow oxidation of ammonia during the expansion stroke. A lower consumption of N2O in post-flame reactions is observed for early injection timings, caused by misdirected ammonia spray causing low temperatures outside the piston bowl. This increases N2O concentrations during the expansion stroke of up to 50%, whereas simultaneous injections minimize ammonia dispersion into the squish area, reducing N2O concentrations by 37%. Ensuring proper ammonia injection direction and utilizing the pilot fuel to interact with the ammonia spray reduces the occurrence of phenomena resulting in N2O accumulation. The results of this study contribute to the understanding of N2O formation, consumption, and accumulation, facilitating the optimization of direct ammonia injection strategies.publishedVersio
Shellfish and shorebirds from the East-Asian Australian flyway as bioindicators for unknown per- and polyfluoroalkyl substances using the total oxidizable precursor assay
Full text linkPer- and polyfluoroalkyl substances (PFAS) have gained significant global attention due to their extensive industrial use and harmful effects on various organisms. Among these, perfluoroalkyl acids (PFAAs) are well-studied, but their diverse precursors remain challenging to monitor. The Total Oxidizable Precursor (TOP) assay offers a powerful approach to converting these precursors into detectable PFAAs. In this study, the TOP assay was applied to samples from the East Asian-Australian Flyway, a critical migratory route for millions of shorebirds. Samples included shellfish from China's coastal mudflats, key stopover sites for these birds, and blood and liver samples from shorebirds overwintering in Australia. The results showed a substantial increase in perfluorocarboxylic acids (PFCAs) across all sample types following the TOP assay, with the most significant increases in shorebird livers (Sum PFCAs increased by 18,156 %). Intriguingly, the assay also revealed unexpected increases in perfluorosulfonic acids (PFSAs), suggesting the presence of unidentified precursors. These findings highlight the need for further research into these unknown precursors, their sources, and their ecological impacts on shorebirds, other wildlife, and potential human exposure. This study also provides crucial insights into the TOP assay’s strengths and limitations in studying PFAS precursor dynamics in biological matrices.publishedVersio