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  • Outlier classification using autoencoders: Application for fluctuation driven flows in fusion plasmas 

    Kube, Ralph; Bianchi, Filippo Maria; LaBombard, Brian; Brunner, Dan (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-01-16)
    Understanding the statistics of fluctuation driven flows in the boundary layer of magnetically confined plasmas is desired to accurately model the lifetime of the vacuum vessel components. Mirror Langmuir probes (MLPs) are a novel diagnostic that uniquely allow us to sample the plasma parameters on a time scale shorter than the characteristic time scale of their fluctuations. Sudden large-amplitude ...
  • Statistical properties of the plasma fluctuations and turbulent cross-field fluxes in the outboard mid-plane scrape-off layer of Alcator C-Mod 

    Kube, Ralph; Garcia, Odd Erik; Theodorsen, Audun; Kuang, Adam; LaBombard, Brian; Terry, Jim L.; Brunner, Dan (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-12-29)
    The Alcator C-Mod mirror Langmuir probe diagnostic is used to characterize plasma fluctuations in the outboard mid-plane scrape-off layer (SOL). Ohmically heated L-mode plasmas with Greenwald fractions from 0.1 to 0.45 are analyzed. In plasmas with a low line-averaged core density, the radial profiles of the average electron density and temperature feature a two-scale structure with a strong gradient ...
  • 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 ...
  • Evaluation of feature ranking and regression methods for oceanic chlorophyll-a estimation 

    Blix, Katalin; Eltoft, Torbjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-22)
    This paper evaluates two alternative regression techniques for oceanic chlorophyll-a (Chl-a) content estimation. One of the investigated methodologies is the recently introduced Gaussian process regression (GPR) model. We explore two feature ranking methods derived for the GPR model, namely sensitivity analysis (SA) and automatic relevance determination (ARD). We also investigate a second ...
  • Method for detection of leads from Sentinel-1 SAR images 

    Murashkin, Dmitrii; Spreen, Gunnar; Huntemann, Marcus; Dierking, Wolfgang Fritz Otto (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-05)
    The presence of leads with open water or thin ice is an important feature of the Arctic sea ice cover. Leads regulate the heat, gas and moisture fluxes between the ocean and atmosphere and are areas of high ice growth rates during periods of freezing conditions. Here, an algorithm providing an automatic lead detection based on synthetic aperture radar images is described that can be applied to a ...
  • Evaluation of the Weather Research and Forecasting (WRF) model with respect to wind in complex terrain 

    Solbakken, Kine; Birkelund, Yngve (Journal article; Tidsskriftartikkel; Peer reviewed, 2018)
    In this study the performance of the Weather Research and Forecast (WRF) model in a complex and coastal terrain has been evaluated with focus on wind resource assessment. The study area is a small community on the northern part of the island Senja, Norway. The community, with fishery and seafood as its main industry, is being limited by poor grid connection. One of the solutions is to increase ...
  • Does your lab use social media? Sharing three years of experience in science communication 

    Pavlov, Alexey K.; Meyer, Amelie; Rösel, Anja; Cohen, Lana; King, Jennifer; Itkin, Polona; Negrel, Jean; Gerland, Sebastian; Hudson, Stephen R.; Dodd, Paul A.; de Steur, Laura; Mathisen, Stig; Cobbing, Nick; Granskog, Mats A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06-27)
    Effective science communication is essential to share knowledge and recruit the next generation of researchers. Science communication to the general public can, however, be hampered by limited resources and a lack of incentives in the academic environment. Various social media platforms have recently emerged, providing free and simple science communication tools to reach the public and young people ...
  • The asymmetric geospace as displayed during the geomagnetic storm on 17 August 2001 

    Østgaard, Nikolai; Reistad, Jone Peter; Tenfjord, Paul; Laundal, Karl Magnus; Rexer, Theresa; Haaland, Stein; Snekvik, Kristian; Hesse, Michael; Milan, Stephen Eric; Ohma, Anders (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-11-29)
    Previous studies have shown that conjugate auroral features are displaced in the two hemispheres when the interplanetary magnetic field (IMF) has a transverse (<i><sub>Y</sub></i>) component. It has also been shown that a <i>B<sub>Y</sub></i> component is induced in the closed magnetosphere due to the asymmetric loading of magnetic flux in the lobes following asymmetric dayside reconnection when the ...
  • 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 ...
  • 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 ...
  • Retrieving horizontally resolved wind fields using multi-static meteor radar observations 

    Stober, Gunter; Chau, Jorge L.; Vierinen, Juha; Jacobi, Christoph; Wilhelm, Sven (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-08-27)
    Recently, the MMARIA (Multi-static, Multi-frequency Agile Radar for Investigations of the Atmosphere) concept of a multi-static VHF meteor radar network to derive horizontally resolved wind fields in the mesosphere–lower thermosphere was introduced. Here we present preliminary results of the MMARIA network above Eastern Germany using two transmitters located at Juliusruh and Collm, and five receiving ...
  • Survey of conditions for artificial aurora experiments by the second electron gyro-harmonic at EISCAT Troms? using dynasonde data 

    Tsuda, T. T.; Rietveld, Michael T; Kosch, M.J; Oyama, S; Ogawa, Y; Hosokawa, K.; Nozawa, S; Kawabata, T; Mizuno, A (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06-06)
    We report a brief survey of matching conditions for artificial aurora optical experiments utilizing the second electron gyro-harmonic (2.7-MHz frequency) in F region heating with O-mode at the EISCAT Tromsø site using dynasonde data from 2000 to 2017. Our survey indicates the following: The possible conditions for successful artificial aurora experiments are concentrated on twilight hours in both ...
  • Skewed Lorentzian pulses and exponential frequency power spectra 

    Garcia, Odd Erik; Theodorsen, Audun (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-18)
    Frequency power spectra due to a super-position of uncorrelated Lorentzian pulses with a random distribution of amplitudes are considered. For pulses with a constant duration, there is an exponential frequency spectrum which is independent of the degree of pulse overlap and the pulse amplitude distribution. The spectrum is furthermore shown to be unaffected by skewness of the Lorentzian pulses and ...
  • 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 ...
  • Automatic autonomous vision-based power line inspection: A review of current status and the potential role of deep learning 

    Nguyen, van Nhan; Jenssen, Robert; Roverso, Davide (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-09)
    To maintain the reliability, availability, and sustainability of electricity supply, electricity companies regularly perform visual inspections on their transmission and distribution networks. These inspections have been typically carried out using foot patrol and/or helicopter-assisted methods to plan for necessary repair or replacement works before any major damage, which may cause power outage. ...
  • 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 ...
  • Summers with low Arctic sea ice linked to persistence of spring atmospheric circulation patterns 

    Kapsch, Marie-Luise; Skific, Natasa; Graversen, Rune; Tjernström, Michael; Francis, Jennifer A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-30)
    The declining trend of Arctic September sea ice constitutes a significant change in the Arctic climate system. Large yearto-year variations are superimposed on this sea–ice trend, with the largest variability observed in the eastern Arctic Ocean. Knowledge of the processes important for this variability may lead to an improved understanding of seasonal and long-term changes. Previous studies suggest ...
  • 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. ...
  • Numerical and experimental evaluation of high-frequency unfocused polymer transducer arrays 

    Habib, Anowarul; Wagle, Sanat; Decharat, Adit; Melandsø, Frank (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06-12)
    High-frequency unfocused polymer array transducers are developed using an adhesive-free layer-by-layer assembly method. The current paper focuses on experimental and numerical methods for measuring the acoustic performance of these types of array transducers. Two different types of numerical approaches were used to simulate the transducer performance, including a finite element method (FEM) study ...
  • Non-Oberbeck-Boussinesq zonal flow generation 

    Held, M; Wiesenberger, M; Kube, Ralph; Kendl, Alexander (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-26)
    Novel mechanisms for zonal flow (ZF) generation for both large relative density fluctuations and background density gradients are presented. In this non-Oberbeck–Boussinesq (NOB) regime ZFs are driven by the Favre stress, the large fluctuation extension of the Reynolds stress, and by background density gradient and radial particle flux dominated terms. Simulations of a nonlinear full-F gyro-fluid ...

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