Recent additions

  • Formation of an additional density peak in the bottom side of the sodium layer associated with the passage of multiple mesospheric frontal systems 

    Narayanan, Viswanathan Lakshmi; Nozawa, Satonori; Oyama, Shin-Ichiro; Mann, Ingrid; Shiokawa, Kazuo; Otsuka, Yuichi; Saito, Norihito; Wada, Satoshi; Kawahara, Takuya D.; Takahashi, Toru (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-18)
    We present a detailed investigation of the formation of an additional sodium density peak at altitudes of 79–85 km below the main peak of the sodium layer based on sodium lidar and airglow imager measurements made at Ramfjordmoen near Tromsø, Norway, on the night of 19 December 2014. The airglow imager observations of OH emissions revealed four passing frontal systems that resembled mesospheric ...
  • Deep Image Translation With an Affinity-Based Change Prior for Unsupervised Multimodal Change Detection 

    Luppino, Luigi Tommaso; Kampffmeyer, Michael; Bianchi, Filippo Maria; Moser, Gabriele; Serpico, Sebastiano Bruno; Jenssen, Robert; Anfinsen, Stian Normann (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-17)
    Image translation with convolutional neural networks has recently been used as an approach to multimodal change detection. Existing approaches train the networks by exploiting supervised information of the change areas, which, however, is not always available. A main challenge in the unsupervised problem setting is to avoid that change pixels affect the learning of the translation function. We propose ...
  • Two-dimensional TIRF-SIM–traction force microscopy (2D TIRF-SIM-TFM) 

    Barbieri, Liliana; Colin-York, Huw; Korobchevskaya, Kseniya; Li, Di; Wolfson, Deanna; Karedla, Narain; Schneider, Falk; Ahluwalia, Balpreet Singh; Seternes, Tore; Dalmo, Roy Ambli; Dustin, Michael L.; Li, Dong; Fritzsche, Marco (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-12)
    Quantifying small, rapidly evolving forces generated by cells is a major challenge for the understanding of biomechanics and mechanobiology in health and disease. Traction force microscopy remains one of the most broadly applied force probing technologies but typically restricts itself to slow events over seconds and micron-scale displacements. Here, we improve >2-fold spatially and >10-fold temporally ...
  • Reducing Objective Function Mismatch in Deep Clustering with the Unsupervised Companion Objective 

    Trosten, Daniel Johansen; Jenssen, Robert; Kampffmeyer, Michael (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-19)
    Preservation of local similarity structure is a key challenge in deep clustering. Many recent deep clustering methods therefore use autoencoders to help guide the model's neural network towards an embedding which is more reflective of the input space geometry. However, recent work has shown that autoencoder-based deep clustering models can suffer from objective function mismatch (OFM). In order to ...
  • The influence of surface charge on the coalescence of ice and dust particles in the mesosphere 

    Baptiste, Joshua; Williamsen, Connor; Fox, John; Stace, Anthony, J.; Hassan, Muhammad; Braun, Stefanie; Mann, Ingrid; Besley, Elena (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-09)
    Agglomeration of charged ice and dust particles in the mesosphere and lower thermosphere is studied using a classical electrostatic approach, which is extended to capture the induced polarisation of surface charge. Collision outcomes are predicted whilst varying the particle size, charge, dielectric constant, relative kinetic energy, collision geometry and the coefficient of restitution. In addition ...
  • Conjugate ionospheric perturbation during the 2017 solar eclipse 

    Zhang, Shunrong; Erickson, Philip J.; Vierinen, Juha; Aa, Ercha; Rideout, William; Coster, Anthea; Goncharenko, Larisa (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-16)
    We report new findings of total electron content (TEC) perturbations in the southern hemisphere at conjugate locations to the northern eclipse on August 21, 2017. We identified a persistent conjugate TEC depletion by 10%–15% during the eclipse time, elongating along magnetic latitudes with at least ∼5° latitudinal width. As the Moon's shadow swept southward, this conjugate depletion moved northward ...
  • Anomalous transport due to large coherent structures in a magnetized toroidal plasma 

    Fredriksen, Åshild; Pécseli, Hans L; Trulsen, Jan Karsten (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-11-18)
    Anomalous transport due to large coherent structures, or coherent events, is studied experimentally in a magnetized toroidal discharge plasma. The present analysis emphasizes anomalous plasma losses as well as transport of electron thermal energy density across magnetic field lines. The experiment was carried out in the Blaamann device at the University of Tromsø. The diagnostics are based on data ...
  • A New Technique for Investigating Dust Charging in the PMSE Source Region 

    Mahmoudian, Alireza; Kosch, Michael J.; Vierinen, Juha; Rietveld, Michael T (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-21)
    A new technique for investigating dust charging in the PMSE (polar mesospheric summer echoes) source region is proposed and discussed in this paper. The first high-frequency (HF) modulation of the PMSE with varying pump power was employed during a recent experimental campaign at EISCAT (European Incoherent Scatter Scientific Association). Two experiment setups including HF pump power stepping as ...
  • Multi-frequency polarimetric SAR signatures of lead sea ice and oil spills 

    Johansson, Malin; Brekke, Camilla; Spreen, Gunnar (Journal article; Tidsskriftartikkel; Peer reviewed; Conference object; Konferansebidrag, 2017-12-04)
    Synthetic aperture radar is used to identify and monitor oil spills. Separation from oil spill look-alikes is an important part of a fully automatic oil spill detection scheme. Here we investigate the polarimetric signatures for oil spills and newly formed sea ice (a well-known look-alike) in fully polarimetric Radarsat-2 satellite scenes. Using the fully polarimetric scenes we calculate four different ...
  • Multistatic Specular Meteor Radar Network in Peru: System Description and Initial Results 

    Chau, Jorge L.; Urco, Miguel; Vierinen, Juha; Harding, Brian; Clahsen, Matthias; Pfeffer, Nico; Kuyeng, Karim; Milla, Marco; Erickson, Philip J. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-10)
    The mesosphere and lower thermosphere (MLT) region is dominated globally by dynamics at various scales: planetary waves, tides, gravity waves, and stratified turbulence. The latter two can coexist and be significant at horizontal scales less than 500 km, scales that are difficult to measure. This study presents a recently deployed multistatic specular meteor radar system, SIMONe Peru, which can be ...
  • Chip Based Optical Nanoscopy: System Integration and Automation 

    Hansen, Daniel Henry (Mastergradsoppgave; Master thesis, 2019-05-15)
    An integrated photonic chip based nanoscopy system has previously been developed at UiT, which allows for several advantages over conventional total internal reflection fluorescence microscopy and nanoscopy (i.e. super-resolutionnanoscopy). While the proof-of-concept has been demonstrated, there were several important system optimization tasks that were needed for making the ...
  • Can We Automate Diagrammatic Reasoning? 

    Sekh, Arif Ahmed; Dogra, Debi Prasad; Kar, Samarjit; Roy, Partha Pratim; Prosad, Dilip K. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-06)
    Diagrammatic reasoning (DR) problems are well known. However, solving DR problems represented in 4 × 1 Raven’s Progressive Matrix (RPM) form using computer vision and pattern recognition has not yet been tried. Emergence of deep learning techniques aided by advanced computing can be exploited to solve such DR problems. In this paper, we propose a new learning framework by combining LSTM and Convolutional ...
  • Video trajectory analysis using unsupervised clustering and multi-criteria ranking 

    Sekh, Arif Ahmed; Dogra, Debi Prasad; Kar, Samarjit; Roy, Partha Pratim (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-13)
    Surveillance camera usage has increased significantly for visual surveillance. Manual analysis of large video data recorded by cameras may not be feasible on a larger scale. In various applications, deep learning-guided supervised systems are used to track and identify unusual patterns. However, such systems depend on learning which may not be possible. Unsupervised methods relay on suitable features ...
  • Horizontal electric fields from flow of auroral O+(2P) ions at sub-second temporal resolution 

    Tuttle, Sam; Lanchester, Betty; Gustavsson, Björn Johan; Keith Whiter, Daniel; Ivchenko, Nickolay; Fear, R. C.; Lester, Mark (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-07-14)
    Electric fields are a ubiquitous feature of the ionosphere and are intimately linked with aurora through particle precipitation and field-aligned currents. They exhibit order-of-magnitude changes on temporal and spatial scales of seconds and kilometres respectively which are not easy to measure; knowing their true magnitude and temporal variability is important for a theoretical understanding of ...
  • Intermittent fluctuations due to Lorentzian pulses in turbulent thermal convection 

    Decristoforo, Gregor; Theodorsen, Audun; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-08-03)
    Turbulent motions due to flux-driven thermal convection are investigated by numerical simulations and stochastic modeling. Tilting of convection cells leads to the formation of sheared flows and quasi-periodic relaxation oscillations for the energy integrals far from the threshold for linear instability. The probability density function for the temperature and radial velocity fluctuations in the ...
  • Blob interactions in 2D scrape-off layer simulations 

    Decristoforo, Gregor; Militello, Fulvio; Nicholas, Thomas; Omotani, John; Marsden, Chris; Walkden, Nick; Garcia, Odd Erik (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-01)
    Interaction of coherent structures known as blobs in the scrape-off layer of magnetically confined plasmas is investigated. Isolated and interacting seeded blobs, as well as full plasma turbulence, are studied by two-dimensional numerical simulations. The features of the blobs (position, size, amplitude) are determined with a blob tracking algorithm, which identifies them as coherent structures with ...
  • Snow and Ice Thickness Retrievals Using GNSS-R: Preliminary Results of the MOSAiC Experiment 

    Munoz-Martin, Joan Francesc; Perez, Adrian; Camps, Adriano; Ribó, Serni; Cardellach, Estel; Stroeve, Julienne; Nandan, Vishnu; Itkin, Polona; Tonboe, Rasmus; Hendricks, Stefan; Huntemann, Marcus; Spreen, Gunnar; Pastena, Massimiliano (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-10)
    The FSSCat mission was the 2017 ESA Sentinel Small Satellite (S⌃3) Challenge winner and the Copernicus Masters competition overall winner. It was successfully launched on 3 September 2020 onboard the VEGA SSMS PoC (VV16). FSSCat aims to provide coarse and downscaled soil moisture data and over polar regions, sea ice cover, and coarse resolution ice thickness using a combined L-band microwave radiometer ...
  • Hyperspectral Nonlinear Unmixing by Using Plug-and-Play Prior for Abundance Maps 

    Wang, Zhicheng; Zhuang, Lina; Gao, Lianru; Marinoni, Andrea; Zhang, Bing; Ng, Michael K. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-16)
    Spectral unmixing (SU) aims at decomposing the mixed pixel into basic components, called endmembers with corresponding abundance fractions. Linear mixing model (LMM) and nonlinear mixing models (NLMMs) are two main classes to solve the SU. This paper proposes a new nonlinear unmixing method base on general bilinear model, which is one of the NLMMs. Since retrieving the endmembers’ abundances represents ...
  • Millstone Hill ISR Measurements of Small Aspect Angle Spectra 

    Longley, William; Erickson, Philip J.; Vierinen, Juha; Oppenheim, Meers; Lind, Frank David; Dimant, Yakov (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-04)
    The Millstone Hill incoherent scatter (IS) radar is used to measure spectra close to perpendicular to the Earth's magnetic field, and the data are fit to three different forward models to estimate ionospheric temperatures. IS spectra measured close to perpendicular to the magnetic field are heavily influenced by Coulomb collisions, and the temperature estimates are sensitive to the collision operator ...
  • Automatic Grading of Retinal Blood Vessel in Deep Retinal Image Diagnosis 

    Debasis, Maji; Sekh, Arif Ahmed (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-01)
    Automatic grading of retinal blood vessels from fundus image can be a useful tool for diagnosis, planning and treatment of eye. Automatic diagnosis of retinal images for early detection of glaucoma, stroke, and blindness is emerging in intelligent health care system. The method primarily depends on various abnormal signs, such as area of hard exudates, area of blood vessels, bifurcation points, ...

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