Now showing items 174-193 of 393

    • 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; Bokkapittel; Bok; Book; 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 ...
    • Light and photosynthetic microalgae: A review of cellular- and molecular-scale optical processes 

      Lehmuskero, Anni Maria; Chauton, Matilde Skogen; Boström, Tobias (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-08)
      Light and its interaction with microalgae are essential concerns in the context of microalgae studies. The optical properties of microalgae have a great impact on the remote sensing ocean color, underwater light distribution and biomass accumulation, to mention some areas. A deep understanding of these processes requires knowledge on both the physical light interaction mechanisms with algae, and ...
    • Linear scaling Coulomb interaction in the multiwavelet basis, a parallel implementation 

      Jensen, Stig Rune; Juselius, Jonas; Durdek, Antoine Pacifique Romain; Flå, Tor; Wind, Peter; Frediani, Luca (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-08-27)
      We present a parallel and linear scaling implementation of the calculation of the electrostatic potential arising from an arbitrary charge distribution. Our approach is making use of the multi-resolution basis of multiwavelets. The potential is obtained as the direct solution of the Poisson equation in its Green’s function integral form. In the multiwavelet basis, the formally non local ...
    • Live-cell imaging of human spermatozoa using structured illumination microscopy 

      Opstad, Ida Sundvor; Popova, Daria; Acharya, Ganesh; Basnet, Purusotam; Ahluwalia, Balpreet Singh (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-11-05)
      Structural details of spermatozoa are interesting from the perspectives of fundamental biology and growing reproductive health problems. Studies of nanostructural details of these extremely motile cells have been limited to fixed cells, largely using electron microscopy. Here we provide the protocols for and demonstrate live-cell multi-color super-resolution imaging of human spermatozoa using ...
    • Localized mesosphere-stratosphere-troposphere radar echoes from the E region at 69 degrees N: Properties and physical mechanisms 

      Rapp, Markus; Leitert, Lasse; Latteck, Ralph; Zecha, Marius; Hoffmann, Peter; Höffner, Josef; Hoppe, Ulf-Peter; La Hoz, Cesar; Thrane, Eivind (Journal article; Tidsskriftartikkel; Peer reviewed, 2011-02-25)
      We present the first observations, to our knowledge, of a new class of high‐latitude mesosphere‐stratosphere‐troposphere radar echoes from the E region as observed with the Arctic Lidar Observatory for Middle Atmosphere Research wind radar during the period 2004–2008. These echoes occur primarily during the summer months and in the altitude range from 93 to 114 km, with a pronounced peak of maximum ...
    • Long-range memory in internal and forced dynamics of millennium-long climate model simulations 

      Østvand, Lene; Nilsen, Tine; Rypdal, Kristoffer; Divine, Dmitry, V.; Rypdal, Martin wibe (Journal article; Tidsskriftartikkel; Peer reviewed, 2014)
      Northern Hemisphere (NH) temperature records from a palaeoclimate reconstruction and a number of millennium-long climate model experiments are investigated for long-range memory (LRM). The models are two Earth system models and two atmosphere–ocean general circulation models. The periodogram, detrended fluctuation analysis and wavelet variance analysis are applied to examine scaling properties ...
    • Longitudinal development of a substorm brightening arc 

      Aslaksen, Torsten; Shiokawa, K.; Ieda, A.; Nakajima, A.; Sakaguchi, K.; Nomura, R.; Greffen, M.; Spanswick, E.; Donovan, E.; Mende, S. B.; McFadden, J.; Glassmeier, K. H.; Angelopoulos, V.; Miyashita, Y. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)
    • A low-cost coastal buoy for ice and metocean measurements 

      Petrich, Christian; O'Sadnick, Megan Eileen; Kleven, Øystein; Sæther, Irina Vasiljeva (Journal article; Tidsskriftartikkel; Peer reviewed; Conference object; Konferansebidrag, 2019-06)
      Regionally, an ice cover in fjords of mainland Norway may form and break up repeatedly during winter. Due to relatively high water temperatures, the freeze-up process is expected to be related to freshwater-induced stratification in the fjords in conjunction with low air temperatues. In an attempt to identify the variability of water conditions in the fjords leading up to and during ice cover ...
    • Low-dimensionality and predictability of solar wind and global magnetosphere during magnetic storms 

      Zivkovic, Tatjana; Rypdal, Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
      The storm index SYM-H, the solar wind velocity v, and interplanetary magnetic field Bz show no signatures of low-dimensional dynamics in quiet periods, but tests for determinism in the time series indicate that SYM-H exhibits a significant low-dimensional component during storm time, suggesting that self-organization takes place during magnetic storms. Even though our analysis yields no discernible ...
    • Low-frequency radio absorption in Cassiopeia A 

      Arias, Maria; Vink, J; De Gasperin, F; Salas, P; Oonk, JBR; Van Weeren, RJ; Van Amesfoort, AS; Anderson, J; Beck, R; Bell, ME; Bentum, MJ; Best, P; Blaauw, R; Breitling, F; Broderick, JW; Brouw, WN; Bruggen, M; Butcher, HR; Ciardi, B; De Geus, E; Deller, A; Van Dijk, PCG; Duscha, S; Eisloffel, J; Garrett, MA; Grie?meier, JM; Gunst, AW; Van Haarlem, MP; Heald, G; Hessels, J; Horandel, J; Holties, HA; Van Der Horst, AJ; Iacobelli, M; Juette, E; Krankowski, A; Van Leeuwen, J; Mann, G; McKay, Derek; McKean, JP; Mulder, H; Nelles, A; Orru, E; Paas, H; Pandey-Pommier, M; Pandey, VN; Pekal, R; Pizzo, R; Polatidis, AG; Reich, W; Rottgering, HJA; Rothkaehl, H; Schwarz, DJ; Smirnov, O; Soida, M; Steinmetz, M; Tagger, M; Thoudam, S; Toribio, MC; Vocks, C; Van Der Wiel, MHD; Wijers, RAMJ; Wucknitz, O; Zarka, P; Zucca, Philippe M. (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-08)
      <i>Context</i>: Cassiopeia A is one of the best-studied supernova remnants. Its bright radio and X-ray emission is due to shocked ejecta. Cas A is rather unique in that the unshocked ejecta can also be studied: through emission in the infrared, the radio-active decay of <sup>44</sup>Ti, and the low-frequency free-free absorption caused by cold ionised gas, which is the topic of this paper.<p> ...
    • Machine Learning Automatic Model Selection Algorithm for Oceanic Chlorophyll-a Content Retrieval 

      Blix, Katalin; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-17)
      Ocean Color remote sensing has a great importance in monitoring of aquatic environments. The number of optical imaging sensors onboard satellites has been increasing in the past decades, allowing to retrieve information about various water quality parameters of the world’s oceans and inland waters. This is done by using various regression algorithms to retrieve water quality parameters from remotely ...
    • Machine Learning simulations of quad-polarimetric features from dual-polarimetric measurements over sea ice 

      Blix, Katalin; Espeseth, Martine; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06)
      In this paper, we investigated the capabilities of the Gaussian Process Regression (GPR) algorithm in predicting of two quad-polarimetric parameters (relevant for sea ice analysis) from 6-dimensional dual-polarimetric input vectors. The GRP is trained on few hundred samples selected randomly from an image subset, and tested on the entire image. The performance is assessed by visual comparisons, and ...
    • Magnetic field-aligned plasma currents in gravitational fields 

      Garcia, Odd Erik; Leer, Egil; Pecseli, Hans; Trulsen, Jan Karsten (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-03-03)
      Analytical models are presented for currents along vertical magnetic field lines due to slow bulk electron motion in plasmas subject to a gravitational force. It is demonstrated that a general feature of this problem is a singularity in the plasma pressure force that develops at some finite altitude when a plasma that is initially in static equilibrium is set into slow motion. Classical fluid models ...
    • Magnetotelluric signatures of the complex tertiary fold–thrust belt and extensional fault architecture beneath Brøggerhalvøya, Svalbard 

      Beka, Thomas Ibsa; Bergh, Steffen G; Smirnov, Maxim; Birkelund, Yngve (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-18)
      Magnetotelluric (MT) data were recently collected on Brøggerhalvøya, Svalbard, in a 0.003–1000 s period range along a curved WNW–ESE profile. The collected data manifested strong three-dimensional (3D) effects. We modelled the full impedance tensor with tipper and bathymetry included in 3D, and benchmarked the result with determinant data two-dimensional (2D) inversion. The final inversion results ...