| 5491. |
- Agten, Dries, et al.
(författare)
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Modeling of a scalable coupled resonator array for microshutter applications
- 2011
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Ingår i: MME 22, Micromechanics and Micro systems Europe Workshop, June 19-22, 2011, Toensberg, Norway. - 9788278602249 ; , s. 154-157
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Konferensbidrag (refereegranskat)abstract
- In this paper we present the resultsfrom the finite element analysis of a scalablecoupled resonator array for ultrafast microshutterapplications. This new design concept builds on thedesign of a previous microshutter array, but couplesthe shutters to each other to allow them to move in acoupled antiphase resonance mode. Simulations forarray scalability show that the resonance frequencydoes not change significantly when adding rowsor columns to the array. The desired resonancemode stays present during scaling. Analyzingthe sensitivity to changing dimensions results inslightly different amplitudes but no change inphase difference between adjacent shutters at theresonance frequency.
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| 5492. |
- Agung, Alexander, 1972, et al.
(författare)
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Development and Validation of Coupled PARCS/RELAP5 Model for Forsmark NPP at Uprated Power
- 2014
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Ingår i: The 10th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-10), Okinawa, Japan, December 14-18, 2014. ; , s. 1-10
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Konferensbidrag (refereegranskat)abstract
- ABSTRACTThis paper gives an account of the development and validation of an up-to-date coupled neutronic/thermal-hydraulic model for the Swedish Forsmark boiling water reactor. The model will be used for analyses of the consequences of the planned power uprate from 2928 MWth to 3253 MWth.At first, the development of the PARCS and RELAP5 models are presented. On the neutronic side, cross-sections data was generated, allowing feeding PARCS with realistic data. This step was performed by converting the library data file from the power plant using the in-house cross-section interface code. The dependence of the material properties on history effects, burnup, and instantaneous conditions was accounted for, and the full heterogeneity of the core was thus taken into account. Each of the 676 fuel assemblies was modeled individually, while the 161 control rods were grouped into 6 different types. On the thermal-hydraulic side, the model consists of a model for the feedwater system, a model for the reactor vessel that include a model for the core channels, and a model for each of the four steam lines. The fuel assemblies were modeled as twelve flow channels in the core region. The coupling between the two codes is touched upon, with emphasis on the mapping between the hydrodynamic/heat structures and the neutronic nodes.The validation efforts were focusing on benchmarking the code capabilities against measured plant data, both under steady-state and transient conditions. The PARCS standalone model was validated against traversing in-core probe (TIP) measurements, taken at different burnup level with operating power varies from 108% (nominal level) to 120% (uprated level). The coupled PARCS/RELAP5 model was validated against an operational transient. For this validation task, the transient chosen was a turbine trip test, which was performed on May 6, 2013.Comparisons between calculated and measured parameters demonstrate that the coupled model was able to correctly represent the steady-state conditions of the plant. The validation of the coupled model against measured transient plant data was then performed. It has been demonstrated that the coupled model is able to capture the main features of the transient with a sufficient level of accuracy
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| 5493. |
- Agung, Alexander, 1972, et al.
(författare)
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The Role of Swedish Universities in Supporting SSM Activities in the Field of Deterministic Safety Analysis
- 2012
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Ingår i: Prosiding Seminar Keselamatan Nuklir 2012, 4 July 2012, Jakarta. - 1412-3258. ; , s. 1-16
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Konferensbidrag (refereegranskat)abstract
- Research within nuclear safety and radiation protection is necessary in order to maintain the high level of competence required by an expert authority. In the field of reactor safety research, SSM’s goals are to support regulation and contribute to national competence in the area of nuclear safety. A technical support organization on deterministic safety analysis (TSO-DSA) has been set up to help SSM in fulfilling these goals. The TSO-DSA function was then established by SSM at two nuclear universities, i.e. Royal Institute of Technology (KTH) in Stockholm and Chalmers University of Technology in Gothenburg. Activities related to this function have been performed, emphasizing the use of best-estimate coupled codes (i.e. PARCS/RELAP5 and PARCS/TRACE) for the analyse . The activities performed by Chalmers are reported in this paper as examples. The on-going activities give a good example on how the safety authority co-operates with universities. The use of coupled codes gives satisfactory results and in good agreements with measured data. Moreover, it may reveal some phenomena that are difficult to capture with stand-alone codes.
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| 5494. |
- Agung, Alexander, 1972, et al.
(författare)
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Validation of PARCS/RELAP5 Coupled codes against a Load Rejection Transient at the Ringhals-3 NPP
- 2013
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493. ; 257, s. 31 - 44
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Tidskriftsartikel (refereegranskat)abstract
- This article gives an account of the development and validation of the PARCS/RELAP5 model of the Ringhals-3 unit against a load rejection transient, which occurred on November 28, 2010. The third unit of the Ringhals nuclear power plant comprises a 3-loop Westinghouse design pressurized water reactor on the Swedish West Coast.At first, the development of the PARCS and RELAP5 models are presented. On the neutronic side, a unique cross-section interface, allowing feeding PARCS with realistic data, was developed. The dependence of the material constants on history effects, burnup, and instantaneous conditions is accounted for, and the full heterogeneity of the core is thus taken into account. The reflectors are also explicitly represented. On the thermal-hydraulic side, all the 157 fuel assemblies are modeled individually in the code input. The model is furthermore able to handle possible asymmetrical conditions of the flow velocity and temperature fields between the loops. The coupling between the two codes is touched upon, with emphasis on the mapping between the hydrodynamic/heat structures and the neutronic nodes.Comparison between calculated and measured parameters demonstrates that the coupled model is able to correctly represent the steady-state conditions of the plant. The validation of the coupled model against measured transient plant data is then performed. It is demonstrated that the coupled model is able to catch the main features of the transient with a sufficient level of accuracy.
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| 5495. |
- Ahdida, C., et al.
(författare)
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The experimental facility for the Search for Hidden Particles at the CERN SPS
- 2019
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Ingår i: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221 .- 1748-0221. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- The Search for Hidden Particles (SHiP) Collaboration has shown that the CERN SPS accelerator with its 400 GeV/c proton beam offers a unique opportunity to explore the Hidden Sector [1-3]. The proposed experiment is an intensity frontier experiment which is capable of searching for hidden particles through both visible decays and through scattering signatures from recoil of electrons or nuclei. The high-intensity experimental facility developed by the SHiP Collaboration is based on a number of key features and developments which provide the possibility of probing a large part of the parameter space for a wide range of models with light long-lived super-weakly interacting particles with masses up to O(10) GeV/c(2) in an environment of extremely clean background conditions. This paper describes the proposal for the experimental facility together with the most important feasibility studies. The paper focuses on the challenging new ideas behind the beam extraction and beam delivery, the proton beam dump, and the suppression of beam-induced background.
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| 5496. |
- Ahlberg Helgee, Edit, 1986
(författare)
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Atomistic Simulation of Interfaces: Proton transport across BaZrO3 grain boundaries
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to the negative environmental effects of fossil fuels it is necessary to develop technology that may reduce or eliminate the need for oil and coal. Fuel cells are highly important in this context as they provide an efficient way of converting chemical energy into electrical energy. However, the development is hampered by a lack of electrolyte materials able to function at temperatures high enough to enable use of hydrocarbon fuels, yet low enough to avoid the wear on component materials caused by high operating temperatures. Solid oxide proton conductors are found to have several of the characteristics of a good electrolyte material in this temperature range, but increasing the conductivity to the level needed in practical applications remains a challenge. The aim of this thesis is to elucidate microscale phenomena that affect the performance of proton-conducting oxides. The material under investigation is BaZrO3, which is regarded as a promising electrolyte material due to its chemical stability and high grain interior conductivity. However, the grain boundaries in the material are highly resistive and lower the total conductivity. The cause of this high grain boundary resistivity has been investigated using atomistic simulations and thermodynamic modelling. Particular attention is devoted to the role of defect segregregation to the grain boundaries.From atomistic simulations it has been found that positively charged defects such as oxygen vacancies and protons segregate to the grain boundaires of BaZrO3. The accumulation of positive charge in the grain boundaries creates a potential barrier and leads to depletion of positive mobile defects from the surrounding region, impeding transport across the boundary. Thermodynamic models have been used to determine the height of the potential barrier resulting from segregation of positive defects, and the results compare well with experimental findings.
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| 5497. |
- Ahlborg, Helene, 1980
(författare)
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Changing energy geographies: The political effects of a small-scale electrification project
- 2018
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Ingår i: Geoforum. - : Elsevier BV. - 0016-7185. ; 97, s. 268-280
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Tidskriftsartikel (refereegranskat)abstract
- This article contributes theoretically and empirically to our understanding about how a transition to ‘modern and sustainable energy for all’ may reconfigure the life of citizens who live ‘outside the grid’ in rural communities in sub-Saharan Africa. My inquiry is inspired by the question posed by James Ferguson and Tania Murray Li: what do development schemes do? I analyse a renewable energy pilot project in Tanzania that was implemented by an NGO, which eventually failed to continue its service delivery but still produced important effects. Conceptually, I build on and extend previous arguments about how development projects produce depoliticizing effects, have ambiguous effects, and reproduce unequal relations of power. Building on feminist and sociotechnical relational approaches to power, I identify when and where in the encounter between energy project and local community that these, and other, effects emerge. Case study data was collected by qualitative methodology, and consists of project documentation, observation, and interviews with actors involved. The study shows how particular material, social, emotional, and economic effects emerged from the encounter between the project and local society. Feedback between technical problems, financial difficulties, and social tensions created a downward spiral resulting in system failure. It had negative effects on the credibility of actors and on trust relations. I argue that asking what decentralized electrification schemes actually ‘do’ can provide insight relevant to energy geography, as the focus on effects reveals the sociotechnical and political relations through which electricity becomes possible and how it may reconfigure local places. The case study shows why and how a small-scale, renewable energy project only temporarily repositioned actors and places, produced ambiguous effects, and maintained unequal power relations.
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| 5498. |
- Ahlborg, Helene, 1980, et al.
(författare)
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Mismatch Between Scales of Knowledge in Nepalese Forestry: Epistemology, Power, and Policy Implications
- 2012
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Ingår i: Ecology and Society. - 1708-3087. ; 17:4
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Tidskriftsartikel (refereegranskat)abstract
- The importance of scale dynamics and scale mismatches for outcomes of natural resource management has been widely discussed. In this article we develop theoretically the concept of ‘knowledge scales’ and illustrate it through empirical examples. We define scales of knowledge as the temporal and spatial extent and character of knowledge held by individuals and collectives, and argue that disparate scales of knowledge are an important ‘scale mismatch,’ which together with scale politics, lead to conflicts in Nepalese forest management. We reveal how there are multiple positions within local knowledge systems and how these positions emerge through people’s use of and relations to the forest, in a dynamic interaction between the natural environment and relations of power such as gender, literacy, and caste. Nepalese forestry is a realm in which power and scales of knowledge are being coproduced in community forestry, at the interface of material and symbolic practices in use of forest resources, and in contestations of social-political relations. Further, we reflect upon the importance of clear and precise use of scale concepts and present a methodological approach using triangulation for divergence, enabling researchers and practitioners involved in natural resource management to reveal scale mismatches and politics.
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| 5499. |
- Ahlborg, Helene, 1980, et al.
(författare)
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Powering institutions for development - Organizational strategies for decentralized electricity provision
- 2018
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Ingår i: Energy Research and Social Science. - : Elsevier BV. - 2214-6296. ; 38, s. 77-86
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Tidskriftsartikel (refereegranskat)abstract
- The study addresses the question of how to achieve and sustain well-functioning local service delivery in institutionally difficult contexts, characterised by low levels of generalised trust, widespread corruption and poor institutions. We study a relatively successful case of decentralized electrification in Tanzania, and the process whereby an international NGO establishes a small-scale hydropower system with a local utility to own and operate it. Building on institutional theory, we investigate how to build trust in an organization, through a strategy of credible commitment; and how free-riding problems can be handled in a local development project. The qualitative study includes 119 semistructured interviews with project staff, villagers, and local and district government, observations and document analysis. The results indicate the importance of a positive ‘history of play’, sustained over time, and keeping distance from corrupt institutions, in order to build trust. Strict enforcement of rules was decisive for handling free riding behaviours, and impartiality in enforcement for perceptions of legitimacy and trustworthiness. Deviations undermined relations of trust. The results add nuance to more generic theoretical propositions and provide insights on un/intended consequences of institutional strategies. These are relevant for creating and sustaining local service organizations for electricity access and other public goods.
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| 5500. |
- Ahlborg, Helene, 1980
(författare)
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Stakeholder-student interactions in engineering education: involving busy experts in project-based courses
- 2023
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Ingår i: Proceedings Chalmers Conference on Teaching and Learning 2023. - 9789188041548 ; , s. 38-45
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Konferensbidrag (refereegranskat)abstract
- Project based learning (PjBL) is increasingly used in engineering courses as a student-centred approach for designing and improving solutions for real-world problems. A key feature of PjBL is the interaction between the problem “owner” and the students who work with the given task. Previous literature documents these interactions primarily from the perspective of students and teachers, leaving us ignorant of the stakeholders’ experience. Undertaken within a larger development process of creating an entirely new project-based Bachelor course at Chalmers, the aim of this study is to better understand how to work with city official as stakeholders and owners of the complex real world problems in the course. The process entailed negotiations with the city government officials, ensuring their participation and engagement in the course. Qualitative data collection provides the basis for comparing expectations of stakeholders, students, and teachers with outcomes. Three components ensured long-term stakeholder involvement: relevant projects; clear rules of engagement for student-stakeholder interaction and; a final conference where students present results to stakeholder.
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