Artikler, rapporter og annet (fysikk og teknologi): Nye registreringer

Viser treff 481-500 av 1062

    • Free-standing tantalum pentoxide waveguides for gas sensing in the mid-infrared 

      Vlk, Marek; Datta, Anurup; Alberti, Sebastian; Murugan, Ganapathy Senthil; Aksnes, Astrid; Jagerska, Jana (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-23)
      Typical applications of integrated photonics in the mid-infrared (MIR) are different from near-infrared (telecom) range and, in many instances, they involve chemical sensing through MIR spectroscopy. Such applications necessitate tailored designs of optical waveguides. Both cross-sectional designs and processing methods of MIR waveguides have been a subject of extensive research, where material ...

    • Semi-supervised target classification in multi-frequency echosounder data 

      Choi, Changkyu; Kampffmeyer, Michael; Handegard, Nils Olav; Salberg, Arnt Børre; Brautaset, Olav; Eikvil, Line; Jenssen, Robert (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-12)
      Acoustic target classification in multi-frequency echosounder data is a major interest for the marine ecosystem and fishery management since it can potentially estimate the abundance or biomass of the species. A key problem of current methods is the heavy dependence on the manual categorization of data samples. As a solution, we propose a novel semi-supervised deep learning method leveraging a few ...

    • Study of waveguide background at visible wavelengths for on-chip nanoscopy 

      Coucheron, David Andre; Helle, Øystein I.; Wilkinson, James S.; Murugan, Ganapathy Senthil; Domínguez, Carlos; Angelskår, Hallvard; Ahluwalia, Balpreet S. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-17)
      On-chip super-resolution optical microscopy is an emerging field relying on waveguide excitation with visible light. Here, we investigate two commonly used high-refractive index waveguide platforms, tantalum pentoxide (Ta<sub>2</sub>O<sub>5</sub>) and silicon nitride (Si<sub>3</sub>N<sub>4</sub>), with respect to their background with excitation in the range 488–640 nm. The background strength from ...

    • Measurement of snow water equivalent using drone-mounted ultra-wide-band radar 

      Jenssen, Rolf Ole R.; Jacobsen, Svein Ketil (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-02)
      The use of unmanned aerial vehicle (UAV)-mounted radar for obtaining snowpack parameters has seen considerable advances over recent years. However, a robust method of snow density estimation still needs further development. The objective of this work is to develop a method to reliably and remotely estimate snow water equivalent (SWE) using UAV-mounted radar and to perform initial field experiments. ...

    • Revisiting Trans-Arctic Maritime Navigability in 2011–2016 from the Perspective of Sea Ice Thickness 

      Zhou, Xiangying; Min, Chao; Yang, Yijun; Landy, Jack Christopher; Mu, Longjiang; Yang, Qinghua (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-14)
      Arctic navigation has become operational in recent decades with the decline in summer sea ice. To assess the navigability of trans-Arctic passages, combined model and satellite sea ice thickness (CMST) data covering both freezing seasons and melting seasons are integrated with the Arctic Transportation Accessibility Model (ATAM). The trans-Arctic navigation window and transit time are thereby obtained ...

    • Short-Term Load Forecasting with Missing Data using Dilated Recurrent Attention Networks 

      Choi, Changkyu; Bianchi, Filippo Maria; Kampffmeyer, Michael; Jenssen, Robert (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-02-06)
      Forecasting the dynamics of time-varying systems is essential to maintaining the sustainability of the systems. Recent studies have discovered that Recurrent Neural Networks(RNN) applied in the forecasting tasks outperform conventional models that include AutoRegressive Integrated Moving Average(ARIMA). However, due to the structural limitation of vanilla RNN which holds unit-length internal ...

    • Faster decline and higher variability in the sea ice thickness of the marginal Arctic seas when accounting for dynamic snow cover 

      Mallett, Robbie; Stroeve, Julienne C.; Tsamados, Michel; Landy, Jack Christopher; Willatt, Rosemary; Nandan, Vishnu; Liston, Glen (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-04)
      Mean sea ice thickness is a sensitive indicator of Arctic climate change and is in long-term decline despite significant interannual variability. Current thickness estimations from satellite radar altimeters employ a snow climatology for converting range measurements to sea ice thickness, but this introduces unrealistically low interannual variability and trends. When the sea ice thickness in the ...

    • Fisheries acoustics and Acoustic Target Classification - Report from the COGMAR/CRIMAC workshop on machine learning methods in fisheries acoustics 

      Handegard, Nils Olav; Andersen, Lars Nonboe; Brautaset, Olav; Choi, Changkyu; Eliassen, Inge Kristian; Heggelund, Yngve; Hestnes, Arne Johan; Malde, Ketil; Osland, Håkon; Ordonez, Alba; Patel, Ruben; Pedersen, Geir; Umar, Ibrahim; Engeland, Tom Van; Vatnehol, Sindre (Research report; Forskningsrapport, 2021-06-15)
      This report documents a workshop organised by the COGMAR and CRIMAC projects. The objective of the workshop was twofold. The first objective was to give an overview of ongoing work using machine learning for Acoustic Target Classification (ATC). Machine learning methods, and in particular deep learning models, are currently being used across a range of different fields, including ATC. The objective ...

    • A comparison of contact charging and impact ionization in low-velocity impacts: implications for dust detection in space 

      Antonsen, Tarjei; Mann, Ingrid; Vaverka, Jakub; Nouzak, Libor; Fredriksen, Åshild (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-15)
      We investigate the generation of charge due to collision between projectiles with sizes below ∼1 µm and metal surfaces at speeds ∼0.1 to 10 km s−1. This corresponds to speeds above the elastic limit and well below speeds where volume ionization can occur. Impact charge production at these low to intermediate speeds has traditionally been described by invoking the theory of shock wave ionization. By ...

    • Cometary plasma science: Open science questions for future space missions 

      Goetz, Charlotte; Herbert, Gunell; Volwerk, Martin; A., Beth; et al, et al, 12 co-authors; Ericksson, A.; Eriksson, A.; Galand, M; Henri, P.; Nilsson, Hans; Simon Wedlund, Cyril; Alho, A.; Andersson, Laila A.; Andre, Nicolas; de Keyser, Johan; Deca, J.; Mann, Ingrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-07)
      Comets hold the key to the understanding of our Solar System, its formation and its evolution, and to the fundamental plasma processes at work both in it and beyond it. A comet nucleus emits gas as it is heated by the sunlight. The gas forms the coma, where it is ionised, becomes a plasma, and eventually interacts with the solar wind. Besides these neutral and ionised gases, the coma also contains ...

    • Electron Bulk Heating at Saturn’s Magnetopause 

      Cheng, I; Achilleos, Nicholas; Masters, A; Lewis, G; Kane, M; Guio, Patrick (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-03-25)
      Magnetic reconnection at the magnetopause (MP) energizes ambient plasma via the release of magnetic energy and produces an “open” magnetosphere allowing solar wind particles to directly enter the system. At Saturn, the nature of MP reconnection remains unclear. The current study examines electron bulk heating at MP crossings, in order to probe the relationship between observed and predicted reconnection ...

    • Fluorescence fluctuation-based super-resolution microscopy using multimodal waveguided illumination 

      Opstad, Ida Sundvor; Hansen, Daniel Henry; Acuña Maldonado, Sebastian Andres; Ströhl, Florian; Priyadarshi, Anish; Tinguely, Jean-Claude; Dullo, Firehun Tsige; Dalmo, Roy Ambli; Seternes, Tore; Ahluwalia, Balpreet Singh; Agarwal, Krishna (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-19)
      Photonic chip-based total internal reflection fluorescence microscopy (c-TIRFM) is an emerging technology enabling a large TIRF excitation area decoupled from the detection objective. Additionally, due to the inherent multimodal nature of wide waveguides, it is a convenient platform for introducing temporal fluctuations in the illumination pattern. The fluorescence fluctuation-based nanoscopy technique ...

    • Cross-platform application of a sea ice classification method considering incident angle dependency of backscatter intensity and its use in separating level and deformed ice 

      Guo, Wenkai; Itkin, Polona; Lohse, Johannes; Johansson, Malin; Doulgeris, Anthony Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2021)
      Wide-swath C-band synthetic aperture radar (SAR) has been used for sea ice classification and estimates of sea ice drift and deformation since it first became widely available in the 1990s. Here, we examine the potential to distinguish surface features created by sea ice deformation using ice type classification of SAR data. To perform this task with extended spatial and temporal coverage, we ...

    • Newly-formed sea ice distinction near the oil platform Prirazlomnaya in the Pechora Sea using polarimetric Radarsat-2 SAR observations 

      Ivonin, Dmitry; Ivanov, Andrey; Johansson, Malin; Brekke, Camilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-01)
      A polarimetric approach developed to discriminate oil slicks and look-alikes was used to study the polarimetric properties of newly-formed ice (NFI) observed near the Prirazlomnaya oil platform. This approach is based on the multipolarization parameter called Resonant to Non-resonant signal Damping (RND), which is related to the ratio between the ice damping and the short wind waves and wave breakings. ...

    • Multi-mission remote sensing of low concentration produced water slicks 

      Johansson, Malin; Skrunes, Stine; Brekke, Camilla; Isaksen, Hugo (Journal article; Tidsskriftartikkel, 2021-04)
      Produced water is legally released from oil platforms and often detected by oil spill detection services despite their low oil concentrations. Using fully-polarimetric RADARSAT-2 and dual-polarimetric Sentinel-1 data we investigate their synthetic aperture radar (SAR) characteristics. Detectability ranges within the SAR and optical Sentinel-2 and PlanetScope images are assessed and compared to in-situ ...

    • Improving Chlorophyll-a Estimation from Sentinel-2 (MSI) in the Barents Sea using Machine Learning 

      Asim, Muhammad; Brekke, Camilla; Mahmood, Arif; Eltoft, Torbjørn; Reigstad, Marit (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-22)
      This article addresses methodologies for remote sensing of ocean Chlorophyll-a (Chl-a), with emphasis on the Barents Sea. We aim at improving the monitoring capacity by integrating in situ Chl-a observations and optical remote sensing to locally train machine learning (ML) models. For this purpose, in situ measurements of Chl-a ranging from 0.014–10.81 mg/m <sup>3</sup> , collected for the years ...

    • Spectral shaping of ring resonator transmission response 

      Yadav, Mukesh; Noh, Jong Wook; Hjelme, Dag Roar; Aksnes, Astrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2021)
      We present a Mach-Zehnder interferometer assisted ring resonator configuration (MARC) to realize resonator transmission spectra with unique spectral signatures and significantly large effective free spectral ranges. Transmission spectra with unique spectral signatures are generated by changing the angular separation between the through port and the drop port waveguides of the ring resonator (RR). ...

    • Radar imaging with EISCAT 3D 

      Stamm, Johann; Vierinen, Juha; Urco, Juan M.; Gustavsson, Björn; Chau, Jorge L. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-04)
      A new incoherent scatter radar called EISCAT 3D is being constructed in northern Scandinavia. It will have the capability to produce volumetric images of ionospheric plasma parameters using aperture synthesis radar imaging. This study uses the current design of EISCAT 3D to explore the theoretical radar imaging performance when imaging electron density in the E region and compares numerical techniques ...

    • Predicting Energy Demand in Semi-Remote Arctic Locations 

      Foldvik Eikeland, Odin; Bianchi, Filippo Maria; Chiesa, Matteo; Apostoleris, Harry; Hansen, Morten; Chiou, Yu-Cheng (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-03)
      Forecasting energy demand within a distribution network is essential for developing strategies to manage and optimize available energy resources and the associated infrastructure. In this study, we consider remote communities in the Arctic located at the end of the radial distribution network without alternative energy supply. Therefore, it is crucial to develop an accurate forecasting model to ...

    • A new auroral phenomenon, the anti-black aurora 

      Nel, A.E.; Kosch, M.J.; Keith Whiter, Daniel; Gustavsson, Björn Johan; Aslaksen, Torun Helene (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-19)
      Black auroras are small-scale features embedded in the diffuse background aurora, typically occurring post-substorm after magnetic midnight and with an eastward drift imposed. Black auroras show a significant reduction in optical brightness compared to the surrounding diffuse aurora, and can appear as slow-moving arcs or rapidly-moving patches and arc segments. We report, for the first time, an even ...