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

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    • The electron energy distribution during HF pumping, a picture painted with all colors. 

      Rietveld, Michael T.; Gustavsson, B.; Sergienko, T.; Grydeland, Tom; La Hoz, Cesar; Kosch, M.J.; Brändström, B.U.E.; Leyser, T.B.; Isham, B.; Gallop, P.; Aso, T.; Ejiri, M.; Steen, A.; Kaila, K.; Jussila, J.; Holma, H. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-07-28)
      The shape of the electron energy distribution has long been a central question in the field of highfrequency radio-induced optical emission experiments. This report presents estimates of the electron energy distribution function, fe(E), from 0 to 60 eV, based on optical multiwavelength (6300, 5577, 8446, 4278 A° ) data and 930-MHz incoherent scatter radar measurements of ion temperature, electron ...

    • Electron Energy Spectrum and Auroral Power Estimation From Incoherent Scatter Radar Measurements 

      Virtanen, Ilkka I.; Gustavsson, Björn Johan; Aikio, Anita; Kero, Antti; Asamura, Kazushi; Ogawa, Yasunobu (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-23)
      Differential energy flux of electrons precipitating into the high‐latitude ionosphere can be estimated from incoherent scatter radar observations of the ionospheric electron density profile. We present a method called ELSPEC for electron spectrum estimation from incoherent scatter radar measurements, which is based on integration of the electron continuity equation and spectrum model selection by ...

    • Electron fishbones: theory and experimental evidence 

      Milovanov, Alexander V.; Zonca, F.; Buratti, P.; Cardinali, A.; Chen, L.; Dong, J.-Q.; Long, Y.-X.; Romanelli, F.; Smeulders, P.; Wang, L.; Wang, Z.-T.; Castaldo, C.; Cesario, R.; Giovannozzi, E.; Marinucci, M.; Ridolfini, V. Pericoli (Journal article; Tidsskriftartikkel; Peer reviewed, 2007-07-19)
      We discuss the processes underlying the excitation of fishbone-like internal kink instabilities driven by supra-thermal electrons generated experimentally by different means: Electron Cyclotron Resonance Heating (ECRH) and by Lower Hybrid (LH) power injection. The peculiarity and interest of exciting these electron fishbones by ECRH only or by LH only is also analyzed. Not only the mode stability ...

    • Electron heating by HF pumping of high-latitude ionospheric F-region plasma near magnetic zenith 

      Leyser, Thomas B; Gustavsson, Björn Johan; Rexer, Theresa; Rietveld, Michael T (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-03-06)
      High-frequency electromagnetic pumping of ionospheric F-region plasma at high and mid latitudes gives the strongest plasma response in magnetic zenith, antiparallel to the geomagnetic field in the Northern Hemisphere. This has been observed in optical emissions from the pumped plasma turbulence, electron temperature enhancements, filamentary magnetic field-aligned plasma density irregularities, and ...

    • Electron velocity distribution function in a plasma with temperature gradient and in the presence of suprathermal electrons: application to incoherent-scatter plasma lines. 

      Guio, Patrick; Lilensten, J.; Kofman, W.; Bjørnå, Noralv (Journal article; Tidsskriftartikkel, 1998-10-31)
      The plasma dispersion function and the reduced velocity distribution function are calculated numerically for any arbitrary velocity distribution function with cylindrical symmetry along the magnetic field. The electron velocity distribution is separated into two distributions representing the distribution of the ambient electrons and the suprathermal electrons. The velocity distribution function of ...

    • Electron-neutral collisions effects on Langmuir probe in the lower E-region ionosphere 

      Brask, Steffen Mattias; Marholm, Sigvald; Di Mare, Francesca; Adhikari, Sayan; Spicher, Andres; Takahashi, T.; Miloch, Wojciech Jacek (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-21)
      We present the first set of particle-in-cell simulations including Monte Carlo collisions between charged and neutral particles used to simulate a cylindrical Langmuir probe in the electron saturation regime with a collisional electron sheath. We use a setup focused on the E-region ionosphere; however, the results of these simulations are analyzed in a general sense using dimensionless values. We ...

    • Electrophoretically deposited carbon nanotube spectrally selective solar absorbers 

      Chen, Zhonghua; Boström, Tobias (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-11)
      Three types of carbon nanotubes(CNT) have been investigated regarding their suitability as spectrally selective solar thermal absorbers.The CNT coatings were electrophoretically deposited on aluminum substrates using kinetically stable CNT aqueous suspensions, of which two CNT aqueous suspensions (N-CNT and P-CNT suspensions) were prepared as part of this study and the third one (T-CNT suspension) ...

    • Elemental Abundances in the Fast Solar Wind Emanating from Chromospheric Funnels 

      Pucci, Stefano; Lie-Svendsen, Øystein; Esser, Ruth (Journal article; Tidsskriftartikkel; Peer reviewed, 2010)
      We carry out a model study to determine whether a funnel-type flow geometry in the solar wind source region leads to sufficiently fast hydrogen flow to offset heavy element gravitational settling and can thus explain why solar wind abundances are not much smaller than photospheric abundances. We find that high first ionization potential (FIP) elements are more susceptible to gravitational settling ...

    • ELM-HTM guided bio-inspired unsupervised learning for anomalous trajectory classification 

      Sekh, Arif Ahmed; Dogra, Debi Prosad; Kar, Samarjit; Roy, Partha Pratim; Prasad, Dilip K. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-23)
      Artificial intelligent systems often model the solutions of typical machine learning problems, inspired by biological processes, because of the biological system is faster and much adaptive than deep learning. The utility of bio-inspired learning methods lie in its ability to discover unknown patterns, and its less dependence on mathematical modeling or exhaustive training. In this paper, we propose ...

    • Emulating sentinel-1 Doppler radial ice drift measurements using envisat ASAR data 

      Kræmer, Thomas; Johnsen, Harald; Brekke, Camilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-05)
      Using data from the Envisat Advanced Synthetic Aperture Radar (ASAR) instrument, this paper demonstrates how the high-precision radial surface velocity product, which will become available with the European Space Agency's Sentinel-1 satellite, can complement the analysis of sea ice motion. High-resolution Doppler frequency measurements are used to estimate the subsecond line-of-sight motion of ...

    • Endocytic motif on a biotin-tagged hiv-1 env modulates the co-transfer of env and gag during cell-to-cell transmission 

      Barría, María Inés; Alvarez, Raymond A.; Law, Kenneth; Wolfson, Deanna; Huser, Thomas; Chen, Benjamin K. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-31)
      During HIV-1 transmission through T cell virological synapses, the recruitment of the envelope (Env) glycoprotein to the site of cell–cell contact is important for adhesion and for packaging onto nascent virus particles which assemble at the site. Live imaging studies in CD4 T cells have captured the rapid recruitment of the viral structural protein Gag to VSs. We explored the role of endocytic ...

    • Energy budget diagnosis of changing climate feedback 

      Cael, B. B.; Bloch-Johnson, Jonah; Ceppi, Paulo; Fredriksen, Hege-Beate; Goodwin, Philip; Gregory, Jonathan M.; Smith, Christopher J.; Williams, Richard G. (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-04-21)
      The climate feedback determines how Earth’s climate responds to anthropogenic forcing. It is thought to have been more negative in recent decades due to a sea surface temperature “pattern effect,” whereby warming is concentrated in the western tropical Pacific, where nonlocal radiative feedbacks are very negative. This phenomenon has however primarily been studied within climate models. We diagnose ...

    • Energy conversion in cometary atmospheres - Hybrid modeling of 67P/Churyumov-Gerasimenko 

      Lindkvist, Jesper; Hamrin, Maria; Gunell, Herbert; Nilsson, Hans; Wedlund, Cyril Simon; Kallio, Esa; Mann, Ingrid; Pitkänen, Timo; Karlsson, Tomas (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-08-21)
      <i>Aims</i>: We wish to investigate the energy conversion between particles and electromagnetic fields and determine the location where it occurs in the plasma environment of comets.<p> <p><i>Methods</i>: We used a hybrid plasma model that included photoionization, and we considered two cases of the solar extreme ultraviolet flux. Other parameters corresponded to the conditions of comet ...

    • Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation 

      Schlatter, Nicola M.; Ivchenko, Nickolay; Sergienko, T; Gustavsson, Björn Johan; Brändström, B. U. E. (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Natural enhancements in the backscattered power of incoherent scatter radars up to 5 orders of magnitudes above the thermal backscatter are sometimes observed at high latitudes. Recently observations of enhancements in the backscattered power including a feature at zero Doppler shift have been reported. These enhancements are limited in altitude to tens of kilometers. The zero Doppler shift ...

    • Enhancement of stratospheric aerosols after solar proton event. 

      Shumilov, O.I.; Henriksen, K.; Kasatkina, E.A.; Vashenyuk, E.V. (Journal article; Tidsskriftartikkel, 1996)
      The lidar measurements at Verhnetulomski observatory (68.6¡N, 31.8¡E) at Kola peninsula detected a considerable increase of stratospheric aerosol concentration after the solar proton event of GLE (ground level event) type on the 16/02/84. This increase was located at precisely the same altitude range where the energetic solar protons lost their energy in the atmosphere. The aerosol layer ...

    • Ensemble Conformalized Quantile Regression for Probabilistic Time Series Forecasting 

      Jensen, Vilde; Bianchi, Filippo Maria; Anfinsen, Stian Normann (Journal article; Tidsskriftartikkel, 2022-11-04)
      This article presents a novel probabilistic forecasting method called ensemble conformalized quantile regression (EnCQR). EnCQR constructs distribution-free and approximately marginally valid prediction intervals (PIs), which are suitable for nonstationary and heteroscedastic time series data. EnCQR can be applied on top of a generic forecasting model, including deep learning architectures. EnCQR ...

    • The environment-induced cracking of as-annealed Ni3(Si,Ti) and Ni3(Si,Ti) with 2Mo in sodium chloride solutions 

      Priyotomo, Gadang; Wagle, Sanat; Okitsu, Kenji; Iwase, Akihiro; Kaneno, Yasuyuki; Nishimura, Rokuro; Takasugi, Takayuki (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-01)
      Background The environment-induced cracking (EIC) of as-annealed Ni3(Si,Ti) and Ni3(Si,Ti) with 2Mo has been researched as functions of applied stress, chloride ion concentration, test temperature, and pH. Methods The investigation of EIC was carried out by applying a constant method in NaCl solutions. Results The EIC susceptibility of both intermetallic compounds increased with ...

    • Episodically Active Asteroid 6478 Gault 

      Jewitt, David; Kim, Yoonyoung; Luu, Jane; Rajagopal, Jayadev; Kotulla, Ralf; Ridgway, Susan; Liu, Wilson (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-05-06)
      We present imaging and spectroscopic observations of 6478 Gault, a ~6 km diameter inner main-belt asteroid currently exhibiting strong, comet-like characteristics. Three distinct tails indicate that ultra-slow dust (ejection speed 0.15 ± 0.05 m s−1) was emitted from Gault in separate episodes beginning UT 2018 October 28 ± 5 (Tail A), UT 2018 December 31 ± 5 (Tail B), and UT 2019 February 10 ± 7 ...

    • Errors in Simple Climate Model Emulations of Past and Future Global Temperature Change 

      Jackson, Lawrence S.; Maycock, Amanda C.; Andrews, Timothy; Fredriksen, Hege-Beate; Smith, Christopher J.; M. Forster, Piers (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-08-04)
      Climate model emulators are widely used to generate temperature projections for climate scenarios, including in the recent Intergovernmental Panel on Climate Change Sixth Assessment Report. Here we evaluate the performance of a two-layer energy balance model in emulating historical and future temperature projections from Coupled Model Intercomparison Project Phase 6 models. We find that emulation ...

    • Estimates of the size distribution of meteoric smoke particles from rocket-borne impact probes 

      Antonsen, Tarjei; Havnes, Ove; Mann, Ingrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-26)
      Ice particles populating noctilucent clouds and being responsible for polar mesosphericsummer echoes exist around the mesopause in the altitude range from 80 to 90 km during polar summer.The particles are observed when temperatures around the mesopause reach a minimum, and it is presumedthat they consist of water ice with inclusions of smaller mesospheric smoke particles (MSPs). This workprovides ...