| 1. |
- Berg, Lars-Erik, et al.
(författare)
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Introduktion av värmekameror i undervisningen vid Lillerudsgymnasiet
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Vi har bedrivit en forskningscirkel med syfte att utvärdera värmekameran som visualiseringsteknik i olika ämnen på naturbruksprogrammet genom att planera, genomföra och reflektera kring lektionsupplägg, där elever har fått möjlighet att använda värmekameror med olika grad av styrning. Resultatet visar att värmekameran har många skilda tillämpningsområden inom lantbruk och djurhållning och kan användas i undervisningen som ett verktyg för elevers praktiska undersökningar av t.ex. djurs fysiologi, eller som ett mätinstrument då tillfälle ges, t.ex. för att studera juverbölder hos suggor eller temperaturökning när en skruv tar fel gäng. En utmaning i undervisningen är att finna en balans mellan öppenhet och styrning, där eleverna upplever att de har möjlighet att undersöka fenomen de själva är intresserade av, men utifrån ett etablerat, systematiskt arbetssätt. Sammanfattningsvis har vi upplevt användning av värmekameror som ett effektivt och intresseväckande sätt att konkretisera och individanpassa undervisningen på naturbruksprogrammet, vilket vi kan rekommendera andra lärare att prova.
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| 2. |
- Haglund, Anders, 1965, et al.
(författare)
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Recovery of missing samples in Orthogonal Frequency Division Multiplexing signals with optimisation using data carriers
- 2024
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Ingår i: IET Radar, Sonar and Navigation. - 1751-8792 .- 1751-8784. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- A method is proposed for reconstructing an Orthogonal Frequency Division Multiplexing (OFDM) signal that contains data gaps, with the aim to improve demodulation. The main objective is to use the method in a passive radar application with missing data samples and to improve target detection. The OFDM signal is assumed to comply with the Digital Video Broadcasting Terrestrial standard. The proposed recovery method is based on optimisation of a novel objective function, which consists of two parts. The first part is a function of the energy in the out-of-band frequencies, whereas the second, and novel part, uses the location of data carriers in the constellation diagram. The method is evaluated using both simulations and real data. The authors show that the proposed method significantly improves the OFDM signal in just a few iteration steps. The proposed method improved the condition number more than a factor ten thousand millions compared to using the least square method on the out-of-band frequencies only. The authors also decode the symbols with the Viterbi decoding algorithm and show how the required number of iterations with the proposed algorithm depends on the amount of missing samples and on the Signal-to-Noise Ratio in order to achieve a Bit Error Rate of less than one in one hundred thousand millions.
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| 3. |
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| 4. |
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| 5. |
- Haglund, Åsa, 1976, et al.
(författare)
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Out of the blue: UV VCSELs
- 2022
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - 0277-786X .- 1996-756X. ; PC12001
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Konferensbidrag (refereegranskat)abstract
- In recent years, there has been tremendous improvement in the performance of blue-emitting vertical-cavity surface-emitting lasers (VCSELs) and they are now on the cusp of commercialization. We will summarize state-of-the-art results and outline the main challenges in extending the emission wavelength into the ultraviolet (UV). Our method to simultaneously achieve high-reflectivity mirrors and good cavity length control by selective electrochemical etching has been essential to demonstrate the world’s first UV-B VCSEL. The use of dielectric mirrors, where one material has a negative thermo-optical coefficient, counteracts the inherent red-shift of the resonance wavelength, enabling a temperature-stable emission.
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| 6. |
- Haglund, Åsa, 1976, et al.
(författare)
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The quest for ultraviolet vertical-cavity surface-emitting lasers
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023.
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Konferensbidrag (refereegranskat)abstract
- We daily rely upon vertical-cavity surface-emitting lasers (VCSELs) for facial recognition and data communication. These lasers are now experiencing exponential growth and serves in other applications as well such as oxygen monitoring in combustion processes and in anesthetized patients in hospitals and as a source of heating in industry in the form of a large-sized array. The large interest for this laser class is linked to its beneficial qualities such as low threshold current, circular-symmetric low-divergent output beam, high efficiency, compactness, and low fabrication cost due to on-wafer testing. Due to these advantages, there is a strong push to realize VCSELs in other wavelength regimes, beyond the commercially available infrared and red. This would open completely new markets such as flood lights, projectors, sterilization, and medical diagnosis and treatment.
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| 7. |
- Haglund, Åsa, 1976, et al.
(författare)
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Thin-film UV VCSELs and LEDs by electrochemical etching
- 2022
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - 0277-786X .- 1996-756X. ; PC12022
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Konferensbidrag (refereegranskat)abstract
- We will give an overview of state-of-the-art results and challenges to achieve high-performing III-nitride vertical-cavity surface-emitting lasers (VCSELs), with a particular focus on the requirements to push the emission wavelength into the ultraviolet (UV). Our method to simultaneously achieve high-reflectivity mirrors and good cavity length control by electrochemical etching enabled the world’s first UV-B VCSEL. The use of dielectric mirrors yielded lasers with a very temperature-stable emission wavelength thanks to the negative thermo-optic coefficient of the mirrors. We have used the same etch methodology to also lift-off fully processed LEDs from their growth substrate to improve the light extraction efficiency.
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| 8. |
- Haglund, Åsa, 1976, et al.
(författare)
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UV VCSELs – this is the way
- 2022
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Ingår i: 9th Workshop on Physics and Technology of Semiconductor Lasers.
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Konferensbidrag (refereegranskat)
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| 9. |
- Hjort, Filip, 1991, et al.
(författare)
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Optical microprism cavities based on dislocation-free GaN
- 2020
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 117:23
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Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional growth of nanostructures can be used to reduce the threading dislocation density that degrades III-nitride laser performance. Here, nanowire-based hexagonal GaN microprisms with flat top and bottom c-facets are embedded between two dielectric distributed Bragg reflectors to create dislocation-free vertical optical cavities. The cavities are electron beam pumped, and the quality (Q) factor is deduced from the cavity-filtered yellow luminescence. The Q factor is similar to 500 for a 1000nm wide prism cavity and only similar to 60 for a 600nm wide cavity, showing the strong decrease in Q factor when diffraction losses become dominant. Measured Q factors are in good agreement with those obtained from quasi-3D finite element frequency-domain method and 3D beam propagation method simulations. Simulations further predict that a prism cavity with a 1000nm width will have a Q factor of around 2000 in the blue spectral regime, which would be the target regime for real devices. These results demonstrate the potential of GaN prisms as a scalable platform for realizing small footprint lasers with low threshold currents.
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| 10. |
- Karell, Patrik, et al.
(författare)
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Mammalian nest predation induces small-scale nest site switching in territorial tawny owl (Strix aluco) females
- 2020
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Ingår i: Ornis Fennica. - 0030-5685. ; 97:2, s. 45-52
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Tidskriftsartikel (refereegranskat)abstract
- Nest predation is a major factor affecting fitness in birds. Individuals are expected to respond to nest predation by selecting safe nesting sites and by moving away from risky sites. Thereby, perceived risk or experience of predation should lead to shifts in nest site selection. Experimental studies on behavioural and life-history consequences of nest predation have traditionally manipulated the risk of predation and studied the immediate consequences thereof. Fewer studies have however analysed the behavioural consequences of perceived predation risk to future breeding events and we know little about how sedentary territorial species respond to nest predation. We experimentally manipulated tawny owl (Strix aluco) breeding nest site choice by providing an additional alternative nest box within the territory, nearby the original nesting sites. The new nest box was provided either after a successful reproductive event (control group), or following a failed reproductive event caused by a nest predator (i.e. pine marten Martes martes, predated group). We show that tawny owls generally switched to the alternative nest site in the current breeding season when the nest was predated in the previous year, whereas they used the same nest after a successful breeding. We found no effects of previous predation experience on the probability to breed nor on clutch size. We conclude that small scale movement within the territory are used by tawny owls to minimize predation risk and that the owls use information on past predation events and nest failure to optimize their breeding decision in the following season.
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