Blar i tittel Artikler, rapporter og annet (fysikk og teknologi)

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    • The Everchanging Pulsating White Dwarf GD358 

      Solheim, Jan Erik; Kepler, S.O.; Nather, R. Edward; Gonzalez Perez, Jose M.; Johannessen, Frank; Winget, Don E.; Nitta, Atsuko; Kleinman, S. J.; Metcalfe, Travis; Sekiguchi, Kazuhiro; Xiaojun, Jiang; Sullivan, Denis; Sullivan, Tiri; Janulis, Rimvydas; Meistas, Edmund; Kalytis, Romualdas; Krzesinski, Jurek; Ogloza, Waldemar; O’Donoghue, Darragh; Romero-Colmenero, Encarni; Martinez, Peter; Dreizler, Stefan; Deetjen, Jochen; Nagel, Thorsten; Schuh, Sonja L.; Vauclair, Gerard; Ning, Fu Jian; Chevreton, Michel; Kanaan, Antonio; Costa, Jos´e Eduardo; Costa, Alex Fabiano Murillo; Wood, Matt A.; Silvestri, Nicole; Ahrens, T.J.; Jones, Aaron Kyle; Collins, Ansley E.; Boyer, Martha; Mukadam, Anjum; Klumpe, Eric W.; Larrison, Jesse; Kawaler, Steve; Riddle, Reed; Ulla, Ana; Bradley, Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2003-01-23)
      We report 323 hours of nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23rd to June 8th, 2000. We acquired more than 232 000 independent measurements. We also report on 48 hours of time-series photometric observations in Aug 1996. We detected the non-radial g-modes consistent with degree ℓ = 1 and radial ...

    • Evidence of L-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith 

      Leyser, Thomas B; James, H Gordon; Gustavsson, Björn Johan; Rietveld, Michael T (Journal article; Peer reviewed, 2018-02-21)
      The response of ionospheric plasma to pumping by powerful HF (high frequency) electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association) Heating facility in magnetic zenith. The ...

    • Evidence of low-dimensional chaos in magnetized plasma turbulence 

      Živkovic, Tatjana; Rypdal, Kristoffer (Working paper; Arbeidsnotat, 2008-03-10)
      We analyze probe data obtained from a toroidal magnetized plasma configuration suitable for studies of low-frequency gradient-driven instabilities. These instabilities give rise to field-aligned convection rolls analogous to Rayleigh-Benard cells in neutral fluids, and may theoretically develop similar routes to chaos. When using mean-field dimension analysis, we observe low dimensionality, but ...

    • The evolution in graphitic surface wettability with first-principles quantum simulations: the counterintuitive role of water 

      Lu, Jin-You; Lai, Chia-Yun; Almansoori, Ibraheem; Chiesa, Matteo (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-08-08)
      The surface wettability of graphite has gained a lot of interest in nanotechnology and fundamental studies alike, but the types of adsorptions that dominate its time resolved surface property variations in ambient environment are still elusive. Prediction of the intrinsic surface wettability of graphite from first-principles simulations offers an opportunity to clarify the overall evolution. In this ...

    • Experimental protocol for sea level projections from ISMIP6 stand-alone ice sheet models 

      Nowicki, Sophie; Goelzer, Heiko; Seroussi, Hélène; Payne, Anthony J.; Lipscomb, William H.; Abe-Ouchi, Ayako; Agosta, Cécile; Alexander, Patrick; Asay-Davis, Xylar S; Barthel, Alice; Bracegirdle, Thomas J.; Cullather, Richard; Felikson, Denis; Fettweis, Xavier; Gregory, Jonathan M.; Hattermann, Tore; Jourdain, Nicolas C.; Munneke, Peter Kuipers; Larour, Eric; Little, Christopher M.; Morlighem, Mathieu; Nias, Isabel; Shepherd, Andrew; Simon, Erika; Slater, Donald; Smith, Robin; Straneo, Fiammetta; Trusel, Luke D.; van den Broeke, Michiel R.; Van de Wal, Roderik (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-07-23)
      Projection of the contribution of ice sheets to sea level change as part of the Coupled Model Intercomparison Project Phase 6 (CMIP6) takes the form of simulations from coupled ice sheet–climate models and stand-alone ice sheet models, overseen by the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). This paper describes the experimental setup for process-based sea level change projections ...

    • Explaining decisions of deep neural networks used for fish age prediction 

      Ordonez, Alba; Eikvil, Line; Salberg, Arnt-Børre; Harbitz, Alf; Murray, Sean Meling; Kampffmeyer, Michael (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-06-19)
      Age-reading of fish otoliths (ear stones) is important for the sustainable management of fish resources. However, the procedure is challenging and requires experienced readers to carefully examine annual growth zones. In a recent study, convolutional neural networks (CNNs) have been demonstrated to perform reasonably well on automatically predicting fish age from otolith images. In the present study, ...

    • Explaining doping in material research (Hf substitution in ZnO films) by directly quantifying the van der Waals force 

      Lai, Chia-Yun; Santos Hernandez, Sergio; Moser, Toni; Alfakes, Boulos; Lu, Chun-Yu; Olukan, Tuza Adeyemi; Rajput, Nitul; Boström, Tobias; Chiesa, Matteo (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-02-04)
      Non-monotonic behavior has been observed in the optoelectronic properties of ZnO thin films as doped with Hf (HZO). Here we propose that two competing mechanisms are responsible for such behaviour. Specifically, we propose that provided two crystal orientations dominate film growth, only one of them might be responsible for direct Hf substitution. Nonmonotonic behaviour is expected at once by ...

    • Exploring the Potential of Sentinel-1 Ocean Wind Field Product for Near-Surface Offshore Wind Assessment in the Norwegian Arctic 

      Khachatrian, Eduard; Asemann, Patricia; Lihong, Zhou; Birkelund, Yngve; Ezau, Igor; Ricaud, Benjamin (Journal article; Tidsskriftartikkel; Peer reviewed, 2024-01-24)
      The exploitation of offshore wind resources is a crucial step towards a clean energy future. It requires an advanced approach for high-resolution wind resource evaluations. We explored the suitability of the Sentinel-1 Level-2 OCN ocean wind field (OWI) product for offshore wind resource assessments. The SAR data were compared to in situ observations and three reanalysis products: the global ...

    • Exploring the temporal variation of the solar quadrupole moment from relativistic gravitation contributions: A fortuitous circumstance? 

      Rozelot, JP; Eren, Saliha (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-11-08)
      Due to its oblateness, the Sun carries a solar quadrupole moment playing a key role at the crossroad of fundamental solar physics, astrometry and celestial mechanics. There is nowadays a general agreement on its order of magnitude ( ≈2×10-7 ), but its temporal dependence is still poorly known. Helioseismology led to a variation within the solar cycle by less than 0.04%, not yet ...

    • The Extending of Observing Altitudes of Plasma and Ion Lines During Ionospheric Heating 

      Wu, Jun; Wu, Jian; Rietveld, Michael T; Häggström, I.; Xu, Zhengwen; Zhao, Haisheng (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-26)
      The ultrahigh-frequency observation during an ionospheric heating experiment on 11 March 2014 at the European Incoherent Scatter Scientific Association Tromsø site illustrated a remarkable extension of observing altitudes of the enhanced plasma line and the ion line, implying that the enhanced ion acoustic wave and Langmuir wave should satisfy the Bragg condition within the extending altitude range. ...

    • Extraordinary evanescent field confinement waveguide sensor for mid-infrared trace gas spectroscopy 

      Vlk, Marek; Datta, Anurup; Alberti, Sebastian; Yallew, Henock Demessie; Mittal, Vinita; Murugan, Ganapathy Senthil; Jágerská, Jana (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-29)
      Nanophotonic waveguides are at the core of a great variety of optical sensors. These structures confine light along defined paths on photonic chips and provide light–matter interaction via an evanescent field. However, waveguides still lag behind free-space optics for sensitivity-critical applications such as trace gas detection. Short optical pathlengths, low interaction strengths, and spurious ...

    • Extreme Horizontal Wind Perturbations in the Mesosphere and Lower Thermosphere Over South America Associated With the 2022 Hunga Eruption 

      Poblet, Facundo L.; Chau, Jorge L.; Conte, J. Federico; Vierinen, Juha; Suclupe, Jose; Liu, Alan; Rodriguez, Rodolfo R. (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-06-13)
      On 15 January 2022, the Hunga volcano produced a massive explosion that generated perturbations in the entire atmosphere. Nonetheless, signatures in the mesosphere and lower thermosphere (MLT) have been challenging to identify. We report MLT horizontal wind perturbations using three multistatic specular meteor radars on the west side of South America (spanning more than 3,000 km). The most ...

    • ExtremeEarth meets satellite data from space 

      Hagos, Desta Haileselassie; Kakantousis, Theofilos; Vlassov, Vladimir; Sheikholeslami, Sina; Wang, Tianze; Dowling, Jim; Paris, Claudia; Marinelli, Daniele; Weikmann, Giulio; Bruzzone, Lorenzo; Khaleghian, Salman; Kræmer, Thomas; Eltoft, Torbjørn; Marinoni, Andrea; Pantazi, Despina-Athanasia; Stamoulis, George; Bilidas, Dimitris; Papadakis, George; Mandilaras, George; Koubarakis, Manolis; Troumpoukis, Antonis; Konstantopoulos, Stasinos; Muerth, Markus; Appel, Florian; Fleming, Andrew; Cziferszky, Andreas (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-26)
      Bringing together a number of cutting-edge technologies that range from storing extremely large volumes of data all the way to developing scalable machine learning and deep learning algorithms in a distributed manner and having them operate over the same infrastructure poses unprecedented challenges. One of these challenges is the integration of European Space Agency (ESA)’s Thematic Exploitation ...

    • F-region electron heating by X-mode radiowaves in underdense conditions 

      Gustavsson, Björn Johan; Löfås, H.; Ivchenko, N.; Rietveld, Michael T; Leyser, T. B. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)

    • Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum 

      Wexler, D.B.; Jensen, E.A.; Hollweg, J.V.; Heiles, C.; Efimov, A.I.; Vierinen, J.; Coster, A.J. (Journal article; Peer reviewed; Tidsskriftsartikkel, 2016-12-26)
      Faraday rotation (FR) of transcoronal radio transmissions from spacecraft near superior conjunction enables study of the temporal variations in coronal plasma density, velocity, and magnetic field. The MESSENGER spacecraft 8.4 GHz radio, transmitting through the corona with closest line-of-sight approach 1.63–1.89 solar radii and near-equatorial heliolatitudes, was recorded soon after the deep ...

    • 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 ...

    • Faszination Nano-Staubteilchen im Kosmos - Astronomie als Puzzle 

      Mann, Ingrid (Conference object; Konferansebidrag, 2018)

    • The Fate of Nanodust near the Sun - Comparison of Sputtering and Sublimation lifetimes during CMEs 

      Baumann, Carsten; Myrvang, Margaretha; Stamm, Johann Immanuel; Mann, Ingrid (Conference object; Konferansebidrag, 2018)
      The dust environment in the inner Solar system has not been probed so far, but ESA’s Solar Orbiter (2020) and NASA’s Parker Solar Probe (2018) are about cross the inner solar system. From [1] we expect a layer of trapper Nanodust around the Sun. [2] investigated the interaction of grains with the Solar wind. But what is the dust’s fate when they are struck by a Coronal Mass Ejection (CME). Are they ...

    • Federated Partially Supervised Learning With Limited Decentralized Medical Images 

      Dong, Nanqing; Kampffmeyer, Michael; Voiculescu, Irina; Xing, Eric (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-12-20)
      Data government has played an instrumental role in securing the privacy-critical infrastructure in the medical domain and has led to an increased need of federated learning (FL). While decentralization can limit the effectiveness of standard supervised learning, the impact of decentralization on partially supervised learning remains unclear. Besides, due to data scarcity, each client may have access ...

    • Finite element simulation of transmission and reflection of acoustic waves in the ultrasonic transducer 

      Shukla, Kaushik; Ahmad, Azeem; Ahluwalia, Balpreet Singh; Melandsø, Frank; Habib, Anowarul (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-30)
      In scanning acoustic microscopy (SAM), the image quality depends on several factors such as noise level, resolution, and interaction of the waves with sample boundaries. The theoretical equations for the reflection coefficient and transmission coefficient are suitable for plane boundaries but fail for curved/rough boundaries. We presented a finite element method-based modeling for the loss ...