Now showing items 48-67 of 942

    • Auroral classification ergonomics and the implications for machine learning 

      McKay, Derek; Kvammen, Andreas (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-07-09)
      The machine-learning research community has focused greatly on bias in algorithms and have identified different manifestations of it. Bias in training samples is recognised as a potential source of prejudice in machine learning. It can be introduced by the human experts who define the training sets. As machine-learning techniques are being applied to auroral classification, it is important to identify ...
    • Auroral Image Classification With Deep Neural Networks 

      Kvammen, Andreas; Wickstrøm, Kristoffer Knutsen; McKay, Derek; Partamies, Noora (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-10-05)
      Results from a study of automatic aurora classification using machine learning techniques are presented. The aurora is the manifestation of physical phenomena in the ionosphere‐magnetosphere environment. Automatic classification of <i>millions</i> of auroral images from the Arctic and Antarctic is therefore an attractive tool for developing auroral statistics and for supporting scientists to study ...
    • Auroral ion acoustic wave enhancement observed with a radar interferometer system 

      Schlatter, Nicola M.; Belyey, Vasyl; Gustavsson, Björn Johan; Ivchenko, Nickolay; Whiter, Daniel; Dahlgren, Hanna; Tuttle, Sam; Grydeland, Tom (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-07-20)
      Measurements of naturally enhanced ion acoustic line (NEIAL) echoes obtained with a five-antenna interferometric imaging radar system are presented. The observations were conducted with the European Incoherent SCATter (EISCAT) radar on Svalbard and the EISCAT Aperture Synthesis Imaging receivers (EASI) installed at the radar site. Four baselines of the interferometer are used in the analysis. Based ...
    • Auroral molecular-emission effects on the atomic oxygen line at 777.4 nm 

      Oyama, Shin-Ichiro; Tsuda, Takuo T.; Hosokawa, Keisuke; Ogawa, Yasunobu; Miyoshi, Yoshizumi; Kurita, Satoshi; Kero, Antti; Fujii, Ryochi; Tanaka, Yoshimasa; Mizuno, Akira; Kawabata, Tetsuya; Gustavsson, Björn Johan; Leyser, Thomas (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-10-16)
      One of the representative auroral emission lines that radiates from F-region heights and is measurable on the ground is the 777.4 nm line from excited atomic oxygen. This line has been adopted, along with another E-region emission line, for example 427.8 nm, to estimate the mean energy and total energy flux of precipitating auroral electrons. The influence of emissions from part of the molecular ...
    • The auroral red line polarisation: modelling and measurements 

      Lilensten, J.; Bommier, V.; Barthelemy, M; Lamy, Herve; Bernard, D; Moen, Jøran Idar; Johnsen, Magnar Gullikstad; Løvhaug, Unni Pia; Pitout, Frederic (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-12)
      In this work, we model the polarisation of the auroral red line using the electron impact theory developed by Bommier et al. (2011). This theory enables the computation of the distribution of the Degree of Linear Polarisation (DoLP) as a function of height if the flux of precipitated electrons is provided as input. An electron transport code is used to infer the stationary electron flux at each ...
    • Authenticating the presence of a relativistic massive black hole binary in OJ 287 using its general relativity centenary flare: Improved orbital parameters 

      Dey, Lankeswar; Valtonen, MJ; Gopakumar, A; Zola, S; Hudec, R; Pihajoki, P; Ciprini, S; Matsumoto, K; Sadakane, K; Kidger, M; Nilsson, K; Mikkola, S; Sillanpää, A; Takalo, LO; Lehto, HJ; Berdyugin, A; Piirola, V; Jermak, H; Baliyan, KS; Pursimo, T; Caton, DB; Alicavus, F; Baransky, A; Blay, P; Boumis, P; Boyd, D; Campas Torrent, M; Campos, F; Carrillo Goméz, J; Chandra, S; Chavushyan, V; Dalessio, J; Debski, B; Drozdz, M; Er, H; Erdem, A; Escartin Pérez, A; Fallah Ramazani, V; Filippenko, AV; Gafton, E; Ganesh, S; Garcia, F; Gazeas, K; Godunova, V; Goméz Pinilla, F; Gopinathan, M; Haislip, JB; Harmanen, J; Hurst, G; Janik, J; Jelinek, M; Joshi, A; Kagitani, M; Karjalainen, R; Kaur, N; Keel, WC; Kouprianov, VV; Kundera, T; Kurowski, S; Kvammen, Andreas; Lacluyze, AP; Lee, BC; Liakos, A; Lindfors, E; Lozano de Haro, J; Mugrauer, M; Naves Nogues, R; Neely, AW; Nelson, RH; Ogloza, W; Okano, S; Pajdosz-Śmierciak, U; Pandey, JC; Perri, M; Poyner, G; Provencal, J; Raj, A; Reichart, DE; Reinthal, R; Reynolds, T; Saario, J; Sadegi, S; Sakanoi, T; Salto González, J-L; Sameer, S; Schweyer, T; Simon, A; Siwak, M; Soldán Alfaro, FC; Sonbas, E; Steele, I; Stocke, JT; Strobl, J; Tomov, T; Tremosa Espasa, L; Valdes, JR; Perez, J Valero; Verrecchia, F; Webb, JR; Yoneda, M; Zejmo, M; Zheng, W; Zielinski, P (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-10-05)
      Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations associated with the binary black hole (BBH) central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects ...
    • Auto-correlation function and frequency spectrum due to a super-position of uncorrelated exponential pulses 

      Garcia, Odd Erik; Theodorsen, Audun (Peer reviewed; Journal article; Tidsskriftsartikkel, 2017-03)
      The auto-correlation function and the frequency power spectral density due to a super-position of uncorrelated exponential pulses are considered. These are shown to be independent of the degree of pulse overlap and thereby the intermittency of the stochastic process. For constant pulse duration and a one-sided exponential pulse shape, the power spectral density has a Lorentzian shape which is flat ...
    • Automated tilt compensation in acoustic microscopy 

      Gupta, Shubham Kumar; Habib, Anowarul; Kumar, Prakhar; Melandsø, Frank; Ahmad, Azeem (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-12)
      Scanning acoustic microscopy (SAM) is a potent and nondestructive technique capable of producing three-dimensional topographic and tomographic images of specimens. This is achieved by measuring the differences in time of flight (ToF) of acoustic signals emitted from various regions of the sample. The measurement accuracy of SAM strongly depends on the ToF measurement, which is affected by tilt in ...
    • Automatic autonomous vision-based power line inspection: A review of current status and the potential role of deep learning 

      Nguyen, van Nhan; Jenssen, Robert; Roverso, Davide (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-09)
      To maintain the reliability, availability, and sustainability of electricity supply, electricity companies regularly perform visual inspections on their transmission and distribution networks. These inspections have been typically carried out using foot patrol and/or helicopter-assisted methods to plan for necessary repair or replacement works before any major damage, which may cause power outage. ...
    • Automatic Detection of Low-Backscatter Targets in the Arctic Using Wide Swath Sentinel-1 Imagery 

      Cristea, Anca; Johansson, Malin; Doulgeris, Anthony Paul; Brekke, Camilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-10-12)
      Low backscatter signatures in synthetic aperture radar (SAR) imagery are characteristic to surfaces that are highly smooth and specular reflective of microwave radiation. In the Arctic, these typically represent newly formed sea ice, oil spills, and localized weather phenomena such as low wind or rain cells. The operational monitoring of low backscatter targets can benefit from a stronger integration ...
    • Automatic detection of the mental foramen for estimating mandibular cortical width in dental panoramic radiographs: the seventh survey of the Tromsø Study (Tromsø7) in 2015-2016 

      Edvardsen, Isak Paasche; Teterina, Anna; Johansen, Thomas Haugland; Myhre, Jonas Nordhaug; Godtliebsen, Fred; Bolstad, Napat Limchaichana (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-22)
      Objective To apply deep learning to a data set of dental panoramic radiographs to detect the mental foramen for automatic assessment of the mandibular cortical width.<p> <p>Methods Data from the seventh survey of the Tromsø Study (Tromsø7) were used. The data set contained 5197 randomly chosen dental panoramic radiographs. Four pretrained object detectors were tested. We randomly chose 80% of the ...
    • Automatic fringe pattern enhancement using truly adaptive period-guided bidimensional empirical mode decomposition 

      Gocłowski, Paweł; Trusiak, Maciej; Ahmad, Azeem; Styk, Adam; Mico, Vicente; Ahluwalia, Balpreet Singh; Patorski, Krzysztof (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-02-19)
      Fringe patterns encode the information about the result of a measurement performed via widely used optical full-field testing methods, e.g., interferometry, digital holographic microscopy, moiré techniques, structured illumination etc. Affected by the optical setup, changing environment and the sample itself fringe patterns are often corrupted with substantial noise, strong and uneven background ...
    • Automatic generation of fill-in-the-blank question with corpus-based distractors for e-assessment to enhance learning 

      Das, Bidyut; Majumder, Mukta; Phadikar, Santanu; Sekh, Arif Ahmed (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-09-10)
      Knowledge acquisition is the prime objective of a learner from an educational system and evaluating the learner's knowledge is the eventual goal of an examination process. This paper introduces a system which is able to produce fill‐in‐the‐blank questions to test the knowledge of a learner that he or she has accumulated after reading a course material. The question generation task is subdivided into ...
    • Automatic Grading of Retinal Blood Vessel in Deep Retinal Image Diagnosis 

      Debasis, Maji; Sekh, Arif Ahmed (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-01)
      Automatic grading of retinal blood vessels from fundus image can be a useful tool for diagnosis, planning and treatment of eye. Automatic diagnosis of retinal images for early detection of glaucoma, stroke, and blindness is emerging in intelligent health care system. The method primarily depends on various abnormal signs, such as area of hard exudates, area of blood vessels, bifurcation points, ...
    • Automatic question generation and answer assessment: a survey 

      Das, Bidyut; Majumder, Mukta; Phadikar, Santanu; Sekh, Arif Ahmed (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-03-18)
      Learning through the internet becomes popular that facilitates learners to learn anything, anytime, anywhere from the web resources. Assessment is most important in any learning system. An assessment system can find the self-learning gaps of learners and improve the progress of learning. The manual question generation takes much time and labor. Therefore, automatic question generation from learning ...
    • Automatic Selection of Relevant Attributes for Multi-Sensor Remote Sensing Analysis: A Case Study on Sea Ice Classification 

      Khachatrian, Eduard; Chlaily, Saloua; Eltoft, Torbjørn; Dierking, Wolfgang Fritz Otto; Dinessen, Frode; Marinoni, Andrea (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-26)
      It is of considerable benefit to combine information obtained from different satellite sensors to achieve advanced and improved characterization of sea ice conditions. However, it is also true that not all the information is relevant. It may be redundant, corrupted, or unnecessary for the given task, hence decreasing the performance of the algorithms. Therefore, it is crucial to select an optimal ...
    • An Automatic U-distribution and Markov Random Field Segmentation Algorithm for PolSAR Images 

      Doulgeris, Anthony Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2015)
    • Axial and radial development of the hot electron distribution in a helicon plasma source, measured by a retarding field energy analyzer (RFEA) 

      Buschmann, Lisa Marie; Fredriksen, Åshild (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-10)
      The information about the electron population of a helicon source plasma that expands along a magnetic nozzle is important for understanding the plasma acceleration across the potential drop that forms in the nozzle. The electrons need an energy higher than the potential drop to escape from the source. At these energies the signal of a Langmuir probe is less accurate. An inverted RFEA measures the ...
    • Barents-2.5km v2.0: an operational data-assimilative coupled ocean and sea ice ensemble prediction model for the Barents Sea and Svalbard 

      Röhrs, Johannes; Gusdal, Yvonne; Rikardsen, Edel S. U.; Durán Moro, Marina; Brændshøi, Jostein; Kristensen, Nils Melsom; Fritzner, Sindre Markus; Wang, Keguang; Sperrevik, Ann Kristin; Idzanovic, Martina; Lavergne, Thomas; Debernard, Jens Boldingh; Christensen, Kai Håkon (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-22)
      An operational ocean and sea ice forecast model, Barents-2.5, is implemented for short-term forecasting at the coast off northern Norway, the Barents Sea, and the waters around Svalbard. Primary forecast parameters are sea ice concentration (SIC), sea surface temperature (SST), and ocean currents. The model also provides input data for drift modeling of pollutants, icebergs, and search-and-rescue ...
    • The behavior of electron density and temperature during ionospheric heating near the fifth electron gyrofrequency 

      Wu, Jun; Wu, Jian; Rietveld, Michael T.; Häggström, I.; Zhao, Haisheng; Xu, Zhengwen (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-01-27)
      The experimental phenomena involving the changes in electron temperature and electron density as a function of pump frequency during an ionospheric heating campaign at European Incoherent Scatter near Tromsø, Norway, are reported. When the pump frequency is slightly above the fifth electron gyrofrequency, the UHF radar observation shows some apparent enhancements over a wide altitude range in radar ...