Now showing items 162-181 of 400

    • An interferometer experiment to explore the aspect angle dependence of stimulated electromagnetic emission spectra. 

      Isham, B.; Rietveld, Michael T.; Belyey, Vasyl; Hagfors, T.; Khudukon, B.; La Hoz, Cesar; Brekke, Asgeir; Yurik, R.Yu; Tereshchenko, E.D.; Grill, M.; Heinselman, C. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-01-31)
      When the Earth's ionosphere is irradiated by a radiofrequency (RF) electromagnetic wave of sufficiently high power density and tuned to match a natural E- or F-region plasma frequency, ionospheric magnetoionic wave modes may be excited and may generate RF electromagnetic sideband waves via nonlinear interactions. These secondary emissions, which may then escape from the ionosphere, have been termed ...
    • Interferometric radar observations of filamented structures due to plasma instabilities and their relation to dynamic auroral rays. 

      Grydeland, Tom; Hagfors, T.; Trondsen, T.S.; Blixt, Erik Mårten; Løvhaug, Unni Pia; La Hoz, Cesar (Journal article; Peer reviewed; Tidsskriftartikkel, 2004-04-02)
      Several explanations have been proposed for Naturally Enhanced ion-acoustic Echoes observed at midand high-latitude Incoherent Scatter observatories. A decisive measure for distinguishing between these explanations is whether or not simultaneously observed up- and downshifted enhancement occur simultaneously, or if they are the result of temporal and/or spatial averaging. The EISCAT Svalbard ...
    • Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer 

      Kube, Ralph; Garcia, Odd Erik; Theodorsen, Audun; Brunner, Daniel; Kuang, Adam; LaBombard, Brian; Terry, James L. (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-10)
      The Alcator C-Mod mirror Langmuir probe system has been used to sample data time series of fluctuating plasma parameters in the outboard mid-plane far scrape-off layer. We present a statistical analysis of one second long time series of electron density, temperature, radial electric drift velocity and the corresponding particle and electron heat fluxes. These are sampled during stationary plasma ...
    • Intermittent fluctuations due to uncorrelated Lorentzian pulses 

      Garcia, Odd Erik; Theodorsen, Audun (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-31)
      Fluctuations due to a super-position of uncorrelated Lorentzian pulses with a random distribution of amplitudes and duration times are considered. These are demonstrated to be strongly intermittent in the limit of weak pulse overlap, resulting in large skewness and flatness moments. The characteristic function and the lowest order moments are derived, revealing a parabolic relationship between the ...
    • Intermittent fluctuations in the Alcator C-Mod scrape-off layer 

      Garcia, Odd Erik; Fritzner, Sindre Markus; Kube, Ralph; Cziegler, Istvan; LaBombard, Brian; Terry, Jim L. (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Fluctuations in the boundary region of the Alcator C-Mod tokamak have been analyzed using gas puff imaging data. It is found that the fluctuation amplitudes in the near scrape-off layer follow a normal distribution while the far scrape-off layer fluctuations are dominated by large amplitude bursts due to radial motion of blob-like structures and have a positively skewed and flattened amplitude ...
    • Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas 

      Garcia, Odd Erik; Kube, Ralph; Theodorsen, Audun; Labombard, B; Terry, J.L (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-20)
      Plasma fluctuations in the scrape-off layer of the Alcator C-Mod tokamak in ohmic and high confinement modes have been analyzed using gas puff imaging data. In all cases investigated, the time series of emission from a single spatially resolved view into the gas puff are dominated by large-amplitude bursts, attributed to blob-like filament structures moving radially outwards and poloidally. There ...
    • Interpreting sea surface slicks on the basis of the normalized radar cross-section model using RADARSAT-2 copolarization dual-channel SAR images 

      Dmitry V., Ivonin; Skrunes, Stine; Brekke, Camilla; Ivanov, A. Yu. (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-03-24)
      A simple automatic multipolarization technique for discrimination of main types of thin oil films (of thickness less than the radio wave skin depth) from natural ones is proposed. It is based on a new multipolarization parameter related to the ratio between the damping in the slick of specially normalized resonant and nonresonant signals calculated using the normalized radar cross-section model ...
    • Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes 

      Jewitt, David; Luu, Jane; Rajagopal, Jayadev; Kotulla, Ralf; Ridgway, Susan; Liu, Wilson; Augusteijn, Thomas (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-30)
      We present observations of the interstellar interloper 1I/2017 U1 ('Oumuamua) taken during its 2017 October flyby of Earth. The optical colors B – V = 0.70 ± 0.06, V – R = 0.45 ± 0.05, overlap those of the D-type Jovian Trojan asteroids and are incompatible with the ultrared objects that are abundant in the Kuiper Belt. With a mean absolute magnitude <i>H <sub>V</sub></i> = 22.95 and assuming a ...
    • Investigation of exceptionally radar-dark regions on the lunar nearside 

      Tveito, Torbjørn; Vierinen, Juha; Serrano, Alessandra (Conference object; Konferansebidrag, 2019-08)
      Remote sensing of planetary surfaces is an effective method for gaining knowledge of the processes that shape the planetary bodies in our solar system. This is useful for uncovering the environment of the primordial solar system and to study the current state of the upper crusts of the other planets in our neighborhood. A recent 6-meter wavelength polarimetric radar map of the Moon [?] showed ...
    • Ion-dispersion and rapid electron fluctuations in the cusp : a case study 

      Lunde, June; Buchert, Stephan C; Ogawa, Yasunobu; Hirahara, Masafumi; Seki, Kanako; Ebihara, Yuusuke; Sakanoi, Takeshi; Asamura, Kazushi; Okada, Masaki; Raita, Tero; Häggström, Ingemar (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
    • Ionospheric bow waves and perturbations induced by the 21 August 2017 solar eclipse 

      Zhang, Shun-Rong; Erickson, Philip j.; Goncharenko, Larisa; Coster, Anthea; Rideout, William; Vierinen, Juha (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-04)
      During solar eclipses, the Moon's shadow causes a large reduction in atmospheric energy input, including not only the stratosphere but also the thermosphere and ionosphere. The eclipse shadow has a supersonic motion which is theoretically expected to generate atmospheric bow waves, similar to a fast‐moving river boat, with waves starting in the lower atmosphere and propagating into the ionosphere. ...
    • Irregular structures of the F layer at high latitudes during ionospheric heating. 

      Rietveld, Michael T.; Tereshchenko, E.D.; Kozlova, M.O.; Brekke, Asgeir; Evstafiev, O.V.; Khudukon, B.Z.; Nygren, T. (Journal article; Peer reviewed; Tidsskriftartikkel, 2000)
      Results on heating the ionospheric F region above Tromsø, Norway are presented. The ionosphere was monitored by satellite tomography and amplitude scintillation methods as well as the EISCAT incoherent scatter radar. No effect of heating was observed in the daytime. In the evening and in the pre-midnight sector, noticeable tilts of the F region were observed during heating periods. The tilts overlapped ...
    • Is a net life cycle balance for energy and materials achievable for a zero emission single-family building in Norway? 

      Kristjansdottir, Torhildur Fjola; Houlihan Wiberg, Aoife Anne Marie; Andresen, Inger; Georges, Laurent; Heeren, Niko; Good, Clara; Brattebø, Helge (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-01)
      In this study, the objective is to redesign a previous concept for a single-family Zero greenhouse gas Emission Building (ZEB). The concept is redesigned based on comparing greenhouse gas (GHG) emission loads and compensation from different design solutions applied in Norwegian single-family ZEB pilot buildings and selected sensitivity studies. The objective is to see if a previously developed ZEB ...
    • A K-Wishart Markov random field model for clustering of polarimetric SAR imagery 

      Moser, Gabriele; Akbari, Vahid; Eltoft, Torbjørn; Doulgeris, Anthony Paul; Anfinsen, Stian Normann; Sebastian, Serpico (Conference object; Konferansebidrag, 2011)
    • A K-Wishart Markov random field model for clustering of polarimetric SAR imagery 

      Akbari, Vahid; Moser, Gabriele; Doulgeris, Anthony Paul; Anfinsen, Stian Normann; Eltoft, Torbjørn; Serpico, Sebastian Bruno (Peer reviewed; Book; Bok; Bokkapittel; Chapter, 2011-10-20)
      A clustering method that combines an advanced statistical distribution with spatial contextual information is proposed for multilook polarimetric synthetic aperture radar (PolSAR) data. It is based on a Markov random field (MRF) model that integrates a K-Wishart distribution for the PolSAR data statistics conditioned to each image cluster and a Potts model for the spatial context. Specifically, the ...
    • K2 Campaign 5 observations of pulsating subdwarf B stars: Binaries and super-Nyquist frequencies 

      Reed, Michael D; Armbrecht, EL; Telting, John H; Baran, Andrzej S; Østensen, Roy; Blay, Pere; Kvammen, Andreas; Kuutma, Teet; Pursimo, Tapio; Ketzer, Laura; Jeffery, C. Simon (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-05)
      We report the discovery of three pulsating subdwarf B stars in binary systems observed with the <i>Kepler</i> space telescope during Campaign 5 of K2. EPIC 211696659 (SDSS J083603.98+155216.4) is a g-mode pulsator with a white dwarf companion and a binary period of 3.16 d. EPICs 211823779 (SDSS J082003.35+173914.2) and 211938328 (LB 378) are both p-mode pulsators with main-sequence F companions. The ...
    • Large amplitude blob propagation in the SOL of Alcator C-Mod and comparison to theoretical model 

      Kube, Ralph; Garcia, Odd Erik; LaBombard, Brian; Terry, James L.; Zweben, Stewart (Conference object; Konferansebidrag, 2012)
    • Late summer sea ice segmentation with multi-polarisation SAR features in C- and X-band 

      Fors, Ane Schwenke; Brekke, Camilla; Doulgeris, Anthony Paul; Eltoft, Torbjørn; Renner, Angelika; Gerland, Sebastian (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-09-01)
      In this study we investigate the potential of sea ice segmentation by C- and X-band multi-polarisation synthetic aperture radar (SAR) features during late summer. Five high-resolution satellite SAR scenes were recorded in the Fram Strait covering iceberg- fast first-year and old sea ice during a week with air temperatures varying around zero degrees Celsius. In situ data consisting of sea ice ...
    • Level crossings and excess times due to a superposition of uncorrelated exponential pulses 

      Theodorsen, Audun; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-10)
      A well-known stochastic model for intermittent fluctuations in physical systems is investigated. The model is given by a superposition of uncorrelated exponential pulses, and the degree of pulse overlap is interpreted as an intermittency parameter. Expressions for excess time statistics, that is, the rate of level crossings above a given threshold and the average time spent above the threshold, are ...
    • Level crossings, excess times, and transient plasma-wall interactions in fusion plasmas 

      Theodorsen, Audun; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-04-19)
      Based on a stochastic model for intermittent fluctuations in the boundary region of magnetically confined plasmas, an expression for the level crossing rate is derived from the joint distribution of the process and its derivative. From this the average time spent by the process above a certain threshold level is obtained. This provides novel predictions of plasma–wall interactions due to transient ...