Recent additions

  • Maximizing Interpretability and Cost-Effectiveness of Surgical Site Infection (SSI) Predictive Models Using Feature-Specific Regularized Logistic Regression on Preoperative Temporal Data 

    Kocbek, Primoz; Fijacko, Nino; Soguero-Ruiz, Cristina; Mikalsen, Karl Øyvind; Maver, Uros; Brzan, Petra Povalej; Stozer, Andraz; Jenssen, Robert; Skrøvseth, Stein Olav; Stiglic, Gregor (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-02-19)
    This study describes a novel approach to solve the surgical site infection (SSI) classification problem. Feature engineering has traditionally been one of the most important steps in solving complex classification problems, especially in cases with temporal data. The described novel approach is based on abstraction of temporal data recorded in three temporal windows. Maximum likelihood L1-norm ...
  • A red tide in the pack ice of the Arctic Ocean 

    Olsen, Lasse Mork; Duarte, Pedro; Peralta-Ferriz, Cecilia; Kauko, Hanna Maria; Johansson, Malin; Peeken, Ilka; Różańska-Pluta, Magdalena; Tatarek, Agnieszka; Wiktor, Jozef; Fernández-Méndez, Mar; Wagner, Penelope Mae; Pavlov, Alexey K.; Hop, Haakon; Assmy, Phillipp (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-02)
    In the Arctic Ocean ice algae constitute a key ecosystem component and the ice algal spring bloom a critical event in the annual production cycle. The bulk of ice algal biomass is usually found in the bottom few cm of the sea ice and dominated by pennate diatoms attached to the ice matrix. Here we report a red tide of the phototrophic ciliate <i>Mesodinium rubrum</i> located at the ice-water interface ...
  • Dust trajectory simulations around Sun, Vega, and Fomalhaut 

    Stamm, Johann Immanuel; Czechowski, Andrzej; Mann, Ingrid; Baumann, Carsten; Myrvang, Margaretha (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-06-20)
    <p><i>Context - </i>Vega and Fomalhaut display a thermal emission brightness that can possibly arise from hot dust near the stars, an inner extension of their planetary debris disks. There was brought up an idea that nm-sized dust particles are kept in the vicinity of the stars by electromagnetic forces. This resembles the trapping that model calculations show in the corotating magnetic field in the ...
  • Detection of meteoroid hypervelocity impacts on the Cluster spacecraft: First results 

    Vaverka, Jakub; Pellinen-Wannberg, Asta; Kero, Johan; Mann, Ingrid; De Spiegeleer, Alexandre; Hamrin, Maria; Norberg, Carol; Pitkaenen, Timo (Journal article; Peer reviewed, 2017-06-29)
    We present the first study of dust impact events on one of the Earth‐orbiting Cluster satellites. The events were identified in the measurements of the wide band data (WBD) instrument on board the satellite operating in monopole configuration. Since 2009 the instrument is operating in this configuration due to the loss of three electric probes and is therefore measuring the potential between the ...
  • Single-input and multiple-output surface acoustic wave sensing for damage quantification in piezoelectric sensors 

    Pamwani, Lavish; Habib, Anowarul; Melandsø, Frank; Ahluwalia, Balpreet Singh; Shelke, Amit (Journal article; Peer reviewed, 2018-06-22)
    The main aim of the paper is damage detection at the microscale in the anisotropic piezoelectric sensors using surface acoustic waves (SAWs). A novel technique based on the single input and multiple output of Rayleigh waves is proposed to detect the microscale cracks/flaws in the sensor. A convex-shaped interdigital transducer is fabricated for excitation of divergent SAWs in the sensor. An angularly ...
  • ICEBEAR: An All‐Digital Bistatic Coded Continuous Wave Radar for Studies of the E Region of the Ionosphere 

    Huyghebaert, Devin; Hussey, Glenn; Vierinen, Juha; McWilliams, Kathryn; St‐Maurice, Jean-Pierre (Journal article; Peer reviewed, 2019-04-15)
    The Ionospheric Continuous-wave E region Bistatic Experimental Auroral Radar (ICEBEAR) is a coherent scatter ionospheric radar. It operates at a frequency of 49.5 MHz, which is ideal for observing E region coherent echoes. The radar is located in Saskatchewan, Canada, and is operated by the University of Saskatchewan. The ICEBEAR system uses a continuous-wave (CW) signal and requires isolation between ...
  • Improved LLM Methods Using Linear Regression 

    Zhao, Zihang; Lang, Wenhui; Doulgeris, Anthony Paul; Chen, Lu (Journal article; Peer reviewed, 2017-12-04)
    This paper is focused on investigations of the improved correction of the effect of variation in incidence angle on ScanSAR data. Conventional correction methods (such as LLM, locally linear mapping) typically assume that each target class has a similarity distribution in the middle of the image. The objectives of this study are to extend the correction algorithm to full swath width without any ...
  • Speeding Up Non-Gaussian POLSAR Image Analysis 

    Doulgeris, Anthony Paul; Hu, Dingsheng (Journal article; Peer reviewed, 2017-12-04)
    Non-Gaussian statistical models fit SAR data better than Gaussian-based statistics, in most cases, but are complicated and time-consuming to use for unsupervised image segmentation via probabilistic clustering. The more advanced the model, the more complicated and slow the clustering. The U-distribution has been demonstrated to be one of the most flexible models, capturing the Gaussian/Wishart, the ...
  • 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 ...
  • First Simultaneous Rocket and Radar Detections of Rare Low Summer Mesospheric Clouds 

    Havnes, O.; Latteck, R.; Hartquist, T.W.; Antonsen, T. (Journal article; Peer reviewed, 2018-06-10)
    On 30 June 2016 a layer of dust, possibly meteoric smoke particles (MSPs), was observed with a rocket borne probe at 69.29°N, 16.02°E and altitudes of ~74 km where patchy thin cloud layers, detected with the Middle Atmosphere Alomar Radar System, were present. The rocket traversed a layer with a net positive dust charge density of ~107 unit charges per cubic meters and a number density of neutral ...
  • 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 ...
  • First results from the Njord device for space related plasma experiments 

    Fredriksen, Åshild; Tribulato, Giulio; Watts, Christopher (Conference object; Konferansebidrag, 2007-08-05)
    The Njord device at Aurolab, University of Tromsø, has been constructed to carry out experiments on instabilities and heating in plasma flows and beams, with relevance to near-Earth space plasmas. For plasma production, Njord combines a 13.56 MHz RF source with a Double Plasma chamber equipped with filaments along the walls. The source is equipped dwith two coils operated at 0-6A, providing magnetic ...
  • Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study 

    Wexler, David; Hollweg, J. V.; Efimov, A. I.; Lukanina, L. A.; Coster, Anthea; Vierinen, Juha; Jensen, E. A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-01-31)
    Fluctuations in plasma electron density may play a role in solar coronal energy transport and the dissipation of wave energy. Transcoronal spacecraft radio sounding observations reveal frequency fluctuations (FFs) that encode the electron number density disturbances, allowing an exploration of the coronal compressive wave and advected inhomogeneity models. Primary FF observations from MESSENGER 2009 ...
  • Modeling of photovoltaic power generation and electric vehicles charging on city-scale: A review 

    Shepero, Mahmoud; Munkhammar, Joakim; Widén, Joakim; DK Bishop, Justin; Boström, Tobias (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-19)
    <p>Photovoltaics (PV) and electric vehicles (EVs) are promising technologies for increasing energy efficiency and the share of renewable energy sources in power and transport systems. As regards the deployment, use and system integration of these technologies, spatio-temporal modeling of PV power production and EV charging is of importance for several purposes such as urban planning and power grid ...
  • Gaussian Markov random field priors in ionospheric 3D multi-instrument tomography 

    Norberg, J.; Vierinen, Juha; Roininen, L; Orispää, M.; Kauristie, K; Rideout, W.; Coster, A. J.; Lehtinen, M (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-08-22)
    In ionospheric tomography, the atmospheric electron density is reconstructed from different electron density related measurements, most often from ground-based measurements of satellite signals. Typically, ionospheric tomography suffers from two major complications. First, the information provided by measurements is insufficient and additional information is required to obtain a unique solution. ...
  • Bistatic Observations of the Ocean Surface with HF Radar, Satellite and Airborne Receivers 

    Bernhardt, Paul A.; Siefring, Carl L.; Briczinski, Stanley C.; Vierinen, Juha; Miller, Ethan; Howarth, Andrew; James, H. Gordon; Blincoe, Eugene (Journal article; Peer reviewed, 2017-12-25)
    A new concept has been developed which can view vast regions of the Earth’s surface. Ground HF transmissions are reflected by the ionosphere to illuminate the ocean over a few thousand kilometers. HF receivers detect the radio waves scattered by the sea and land surface. Using the theory of radio wave scatter from ocean surfaces, the HF data is then processed to yield the directional wave-height ...
  • EISCAT 3D: the next generation international atmosphere and geospace research radar 

    Kero, Johan; Kastinen, D; Vierinen, Juha; Grydeland, Tom; Heinselman, Craig J.; Markkanen, Jussi; Tjulin, A. (Journal article; Tidsskriftartikkel, 2019)
    EISCAT_3D is the next generation international atmosphere- and geospace research radar under development in Arctic Europe. Construction have started in September 2017 and the radar system is expected to be operational in the end of 2021. The EISCAT_3D facility will be distributed across three sites in Northern Scandinavia - in Skibotn, Norway, near Kiruna in Sweden, and near Karesuvanto in Finland. ...
  • Next-generation Space Object Radar Tracking Simulator: SORTS++ 

    Kastinen, D; Vierinen, Juha; Kero, Johan; Hesselbach, S; Grydeland, Tom; Krag, Holger (Journal article; Tidsskriftartikkel, 2019)
    We describe the software toolbox SORTS++ which is the next-generation Space Object Radar Tracking Simulator (SORTS). This toolbox is able to simulate general Space Surveillance and Tracking (SST) applications from catalogue maintenance to cold-start performance for radar systems or collections of radar systems. We have applied this toolbox to the EISCAT 3D radar system, currently under construction, ...
  • 2018 Beam-park observations of space debris with the EISCAT radars 

    Vierinen, Juha; Kastinen, D; Markkanen, Jussi; Grydeland, Tom; Kero, Johan; Horstmann, A.; Hesselbach, S.; Kebschull, C.; Røynestad, Elisabeth; Krag, Holger (Journal article; Tidsskriftartikkel, 2019)
    Monitoring the evolution of the space debris environment requires regular radar observations of the space debris population. This study presents the results from 24 hours of beam-park observations of space objects conducted simultaneously with the EISCAT Svalbard and Tromsø radars on and between January 4th and 5th, 2018. The measurements are processed with a new matched filter bank analysis program, ...
  • Quad-Polarimetric SAR for Detection and Characterization of Icebergs 

    Akbari, Vahid; Brekke, Camilla; Doulgeris, Anthony Paul; Storvold, Rune; Sivertsen, Agnar H. (Conference object; Konferansebidrag, 2016)
    This paper evaluates the performance of fully polarimetric SAR data in iceberg detection and characterization. The study aims to explore the potential of RADARSAT-2 SAR data to detect icebergs and growlers in Svalbard that have broken off from the glaciers nearby. To be able to detect iceberg/growlers in a SAR image, a significant contrast between iceberg and background clutter is required. The ...

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