| 1. |
- Aupke, Phil, et al.
(författare)
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Impact of Clustering Methods on Machine Learning-based Solar Power Prediction Models
- 2022
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Ingår i: 2022 IEEE International Smart Cities Conference (ISC2). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665485616
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Konferensbidrag (refereegranskat)abstract
- Prediction of solar power generation is important in order to optimize energy exchanges in future micro-grids that integrate a large amount of photovoltaics. However, an accurate prediction is difficult due to the uncertainty of weather phenomena that impact produced power. In this paper, we evaluate the impact of different clustering methods on the forecast accuracy for predicting hourly ahead solar power when using machine learning based prediction approaches trained on weather and generated power features. In particular, we compare clustering methods using clearness index and K-means clustering, where we use both euclidian distance and dynamic time-warping. For evaluating prediction accuracy, we develop and compare different prediction models for each of the clusters using production data from a swedish SmartGrid. We demonstrate that proper tuning of thresholds for the clearness index improves prediction accuracy by 20.19% but results in worse performance than using K-means with all weather features as input to the clustering.
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| 2. |
- Blomberg, Per
(författare)
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Informell Statistisk Inferens i modelleringssituationer : En studie om utveckling av ett ramverk för att analysera hur elever uttrycker inferenser
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Syftet med denna studie är att bidra med ökad kunskap om lärande och undervisning i informell statistisk inferens. I studien användes en kvalitativ forskningsstrategi inriktad mot prövning och generering av teorier med inspiration av grounded theory. Studiens kunskapsfokus är riktad mot karakterisering av statistiska processer och begrepp där system av begreppsramverk om informell statistisk inferens och modellering utgör en central del av forskningen. För att erhålla adekvat empiri utformades en undervisningssituation där elever engagerades med att planera och genomföra en undersökning. Studien genomfördes i en normal klassrumssituation där undervisningen inriktades mot ett område inom sannolikhet och statistisk där bland annat lådagram och normalfördelning med tillhörande begrepp introduceras. Det empiriska materialet samlades in genom videoinspelning och skriftliga redovisningar. Materialet analyserades genom ett sammansatt ramverk om informell statistisk inferens och modellering. Resultatet av analysen visar exempel på hur elever kan förväntas uttrycka aspekter av informella statistisk inferens då de genomför statistiska undersökningar. Vidare utvecklades ett ramverk som teoretiskt beskriver informell statistisk inferens i modelleringssituationer. Studien pekar på att ISI-modellering har potential att användas för att analysera hur informell statistisk inferens kan komma till uttryck och att identifiera potentiella inlärningsmöjligheter för studenter att utveckla sin förmåga att uttrycka informella statistisk slutledning och att identifiera potentiella inlärningsmöjligheter för elever att utveckla sin förmåga att uttrycka informella inferenser.
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| 3. |
- Hansson, Josef, 1991, et al.
(författare)
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Effects of high temperature treatment of carbon nanotube arrays on graphite : Increased crystallinity, anchoring and inter-tube bonding
- 2020
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Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 31:45
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Tidskriftsartikel (refereegranskat)abstract
- Thermal treatment of carbon nanotubes (CNTs) can significantly improve their mechanical, electrical and thermal properties due to reduced defects and increased crystallinity. In this work we investigate the effect of annealing at 3000 degrees C of vertically aligned CNT arrays synthesized by chemical vapor deposition (CVD) on graphite. Raman measurements show a drastically reduced amount of defects and, together with transmission electron microscope (TEM) diffraction measurements, an increased average crystallite size of around 50%, which corresponds to a 124% increase in Young's modulus. We also find a tendency for CNTs to bond to each other with van der Waals (vdW) forces, which causes individual CNTs to closely align with each other. This bonding causes a densification effect on the entire CNT array, which appears at temperatures >1000 degrees C. The densification onset temperature corresponds to the thermal decomposition of oxygen containing functional groups, which otherwise prevents close enough contact for vdW bonding. Finally, the remaining CVD catalyst on the bottom of the CNT array is evaporated during annealing, enabling direct anchoring of the CNTs to the underlying graphite substrate.
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| 4. |
- Karlsson, Jonas, 1977-, et al.
(författare)
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Performance Evaluation for TCP in Tactical Mobile Ad hoc Networks
- 2012
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Ingår i: Proceedings of International Conference on Wireless Information Networks and Systems. - : SciTePress. - 9789898425737 ; , s. 277-282
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Konferensbidrag (refereegranskat)abstract
- Tactical networks are used in military and rescue operations to provide timely and accurate information to operating teams. Tactical networks have traditionally used long distance narrow band radio links. However, although these links provide robust real-time communication the limited bandwidth makes them less suited for high data-rate applications. To support high-data rate TCP applications such as providing digital images and maps, emerging tactical networks use shorter range but higher data-rate wide band radio links and multi-hop. Due to the requirement of cheap up-front cost, most MANET research has focused on Carrier Sense Multiple Access (CSMA) networks. However, in tactical networks, where bounded delays are important, Time Division Multiple Access (TDMA) can give better possibility to support the Quality of Service needed for real-time communication. The purpose of this paper is to assess and compare the throughput of three state-of-the-art TCP versions and two routing protocols over TDMA based MANETs.
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| 5. |
- Mellroth, Elisabet, 1971-, et al.
(författare)
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Task design for differentiated instruction in mathematics : Manifestations of contradictions in a professional learning community.
- 2021
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Ingår i: Mathematics Teacher Education and Development. - : University of the Sunshine Coast. - 1442-3901. ; 23:3, s. 78-96
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to investigate task design for differentiated instruction in mathematics inprofessional learning communities. Based on the cultural-historical activity theory, we conceptualizea professional learning community as an activity system and use the analytical construct ofcontradictions to give an account of structures that bring forward the teachers’ work. Eight Swedishupper secondary teachers, engaged in designing tasks for differentiated instruction in mixed-abilitymathematics classrooms, are studied. The analysis outlines three contradictions, manifested as threedilemmas, and shows how the teachers, by noticing a dilemma and making it an explicit object ofinquiry, came to address a diversity of issues related to differentiated instruction in mathematics. Forexample, the teachers addressed students’ different learning needs, problem-solving activities for amixed-ability classroom, and design of tasks that are challenging for all students. With input fromour findings on the three dilemmas, we then discuss the design of a task analysis guide as a meansfor facilitating the development of a professional learning community that is inquiry-oriented with astrong content focus on designing tasks for differentiated instruction in mixed-ability mathematicsclassrooms.
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| 6. |
- Nilsson, Daniel, et al.
(författare)
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Ronchi test for characterization of nanofocusing optics at a hard x-ray free-electron laser
- 2012
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Ingår i: Optics Letters. - : Optical Society of America. - 0146-9592 .- 1539-4794. ; 37:24, s. 5046-5048
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the use of the classical Ronchi test to characterize aberrations in focusing optics at a hard x-ray free-electron laser. A grating is placed close to the focus and the interference between the different orders after the grating is observed in the far field. Any aberrations in the beam or the optics will distort the interference fringes. The methodis simple to implement and can provide single-shot information about the focusing quality. We used the Ronchi test to measure the aberrations in a nanofocusing Fresnel zone plate at the Linac Coherent Light Source at 8.194 keV.
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| 7. |
- Solis, Jorge, 1976-, et al.
(författare)
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Analyzing the effect of snow in PV regulator response in a PV solar park
- 2021
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Ingår i: 9th International Conference on Smart Grid, icSmartGrid 2021. - : IEEE. - 9781665445313 ; , s. 72-75
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Konferensbidrag (refereegranskat)abstract
- In the Nordic countries, the snow in the solar panels affects considerably the solar energy production and the detection of its effects can be an issue due to the outdoor climate conditions. Our research aims to develop intelligent control systems for photovoltaic systems that adapts after variable environmental conditions. One of these conditions is the presence of snow or other form of pollution. In this paper, we focus to investigate whether it is possible to detect snow on a solar panel (off-grid) without using additional external sensors as well to investigate how snow affects the efficiency, current and power on a grid-connected solar panel. For this purpose, a set of experiments were proposed and carried out in a PV solar park. © 2021 IEEE.
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