Viser treff 41-60 av 1261

    • GNSS Scintillations in the Cusp, and the Role of Precipitating Particle Energy Fluxes 

      Ivarsen, Magnus Fagernes; Jin, Yaqi; Spicher, Andres; St-Maurice, Jean-Pierre; Park, Jaeheung; Billett, Daniel (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-16)
      Using a large data set of ground-based GNSS scintillation observations coupled with in situ particle detector data, we perform a statistical analysis of both the input energy flux from precipitating particles, and the observed occurrence of density irregularities in the northern hemisphere cusp. By examining trends in the two data sets relating to geomagnetic activity, we conclude that observations ...
    • Automated tilt compensation in acoustic microscopy 

      Gupta, Shubham Kumar; Habib, Anowarul; Kumar, Prakhar; Melandsø, Frank; Ahmad, Azeem (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-12)
      Scanning acoustic microscopy (SAM) is a potent and nondestructive technique capable of producing three-dimensional topographic and tomographic images of specimens. This is achieved by measuring the differences in time of flight (ToF) of acoustic signals emitted from various regions of the sample. The measurement accuracy of SAM strongly depends on the ToF measurement, which is affected by tilt in ...
    • View it like a radiologist: Shifted windows for deep learning augmentation of CT images 

      Østmo, Eirik Agnalt; Wickstrøm, Kristoffer; Radiya, Keyur; Kampffmeyer, Michael; Jenssen, Robert (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-23)
      Deep learning has the potential to revolutionize medical practice by automating and performing important tasks like detecting and delineating the size and locations of cancers in medical images. However, most deep learning models rely on augmentation techniques that treat medical images as natural images. For contrast-enhanced Computed Tomography (CT) images in particular, the signals producing the ...
    • On mechanisms for high-frequency pump-enhanced optical emissions at 557.7 and 630.0gnm from atomic oxygen in the high-latitude F-region ionosphere 

      Leyser, Thomas B.; Sergienko, Tima; Brändström, Urban; Gustavsson, Björn Johan; Rietveld, Michael T. (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-12-13)
      The EISCAT (European Incoherent Scatter Scientific Association) Heating facility was used to transmit powerful high-frequency (HF) electromagnetic waves into the Fregion ionosphere to enhance optical emissions at 557.7 and 630.0 nm from atomic oxygen. The emissions were imaged by several stations of ALIS (Auroral Large Imaging System) in northern Sweden, and the EISCAT UHF incoherent scatter radar ...
    • Impact of the Nares Strait sea ice arches on the long-term stability of the Petermann Glacier ice shelf 

      Prakash, Abhay; Zhou, Qin; Hattermann, Tore; Kirchner, Nina (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-12-12)
      One of the last remaining floating tongues of the Greenland ice sheet (GrIS), the Petermann Glacier ice shelf (PGIS), is seasonally shielded from warm Atlantic water (AW) by the formation of sea ice arches in the Nares Strait. However, continued decline of the Arctic sea ice extent and thickness suggests that arch formation is likely to become anomalous, necessitating an investigation into ...
    • Discriminative multimodal learning via conditional priors in generative models 

      Andrade Mancisidor, Rogelio; Kampffmeyer, Michael Christian; Aas, Kjersti; Jenssen, Robert (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-11-02)
      Deep generative models with latent variables have been used lately to learn joint representations and generative processes from multi-modal data, which depict an object from different viewpoints. These two learning mechanisms can, however, conflict with each other and representations can fail to embed information on the data modalities. This research studies the realistic scenario in which all ...
    • Sub-ppm Methane Detection with Mid-Infrared Slot Waveguides 

      Yallew, Henock Demessie; Vlk, Marek; Datta, Anurup; Alberti, Sebastian; Zakoldaev, Roman A.; Høvik, Jens; Aksnes, Astrid; Jagerska, Jana (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-11-21)
      Hybrid integration of photonic chips with electronic and micromechanical circuits is projected to bring about miniature, but still highly accurate and reliable, laser spectroscopic sensors for both climate research and industrial applications. However, the sensitivity of chip-scale devices has been limited by immature and lossy photonic waveguides, weak light–analyte interaction, and etalon effects ...
    • Machine learning assisted multifrequency AFM: Force model prediction 

      Elsherbiny, Lamiaa; Santos Hernandez, Sergio; Gadelrab, Karim; Olukan, Tuza; Font, Josep; Barcons, Victor; Chiesa, Matteo (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-12-05)
      Multifrequency atomic force microscopy (AFM) enhances resolving power, provides extra contrast channels, and is equipped with a formalism to quantify material properties pixel by pixel. On the other hand, multifrequency AFM lacks the ability to extract and examine the profile to validate a given force model while scanning. We propose exploiting data-driven algorithms, i.e., machine learning packages, ...
    • A comparison of constant false alarm rate object detection algorithms for iceberg identification in L- and C-band SAR imagery of the Labrador Sea 

      Færch, Laust; Dierking, Wolfgang Fritz Otto; Hughes, Nick; Doulgeris, Anthony Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-12-15)
      In this study, we pursue two objectives: first, we compare six different “constant false alarm rate” (CFAR) algorithms for iceberg detection in SAR images, and second, we investigate the effect of radar frequency by comparing the detection performance at C- and L-band. The SAR images were acquired over the Labrador Sea under melting conditions. In an overlapping optical Sentinel-2 image, 492 icebergs ...
    • Data science in wind energy: a case study for Norwegian offshore wind 

      Chen, Hao; Birkelund, Yngve; Zhang, Qixia (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-11-17)
      In the digital and green transitions, rapidly growing renewable energies are accumulating more and more data. Big data gives room to apply emerging data science to solve challenges in the energy sector. Offshore wind power receives accelerating attention due to its sufficient resources and cleanness. This paper uses data science, including statistical analysis and machine learning, to systematically ...
    • Inferring neutral winds in the ionospheric transition region from atmospheric-gravity-wave traveling-ionospheric-disturbance (AGW-TID) observations with the EISCAT VHF radar and the Nordic Meteor Radar Cluster 

      Günzkofer, Florian; Pokhotelov, Dimitry; Stober, Gunter; Mann, Ingrid Brigitte; Vadas, Sharon L.; Becker, Erich; Tjulin, Anders; Kozlovsky, Alexander; Tsutsumi, Masaki; Gulbrandsen, Njål; Nozawa, Satonori; Lester, Mark; Belova, Evgenia; Kero, Johan; Mitchell, Nicholas J.; Borries, Claudia (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-18)
      Atmospheric gravity waves and traveling ionospheric disturbances can be observed in the neutral atmosphere and the ionosphere at a wide range of spatial and temporal scales. Especially at medium scales, these oscillations are often not resolved in general circulation models and are parameterized. We show that ionospheric disturbances forced by upward-propagating atmospheric gravity waves can be ...
    • Ionospheric Flow Vortex Induced by the Sudden Decrease in the Solar Wind Dynamic Pressure 

      Jin, Yaqi; Moen, Jøran Idar; Spicher, Andres; Liu, Jianjun; Clausen, Lasse; Miloch, Wojciech Jacek (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-30)
      Abrupt changes in the solar wind dynamic pressure can greatly affect the Earth's magnetosphere-ionosphere system. We present an ionospheric flow vortex in the morning sector during the sudden decrease in the solar wind dynamic pressure. The flow vortex was clearly observed by both the Hankasalmi radar and the azimuthal scan mode of the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR). The ...
    • 3D refractive index reconstruction from phaseless coherent optical microscopy data using multiple scattering-based inverse solvers - a study 

      Qin, Yingying; Butola, Ankit; Agarwal, Krishna (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-11-27)
      Reconstructing 3D refractive index profile of scatterers using optical microscopy measurements presents several challenges over the conventional microwave and RF domain measurement scenario. These include phaseless and polarization-insensitive measurements, small numerical aperture, as well as a Green's function where spatial frequencies are integrated in a weighted manner such that far-field angular ...
    • Analysis of Deep Convolutional Neural Networks Using Tensor Kernels and Matrix-Based Entropy 

      Wickstrøm, Kristoffer Knutsen; Løkse, Sigurd Eivindson; Kampffmeyer, Michael Christian; Yu, Shujian; Príncipe, José C.; Jenssen, Robert (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-06-03)
      Analyzing deep neural networks (DNNs) via information plane (IP) theory has gained tremendous attention recently to gain insight into, among others, DNNs’ generalization ability. However, it is by no means obvious how to estimate the mutual information (MI) between each hidden layer and the input/desired output to construct the IP. For instance, hidden layers with many neurons require MI estimators ...
    • Analyzing the Impact of Peak-Shaving on Load Reduction and on Battery Energy Storage System Degradation: A Simulation-Based Study in Husøy 

      Kournoutis, Georgios (Mastergradsoppgave; Master thesis, 2023-11-14)
      The island of Husøy, in Northern Senja, Norway, faces numerous voltage quality difficulties, which arise from the consequent surge in electricity demand by the local growing fishing industry. Collaborating with the local distribution system operator (DSO), Arva, the current study explores the implementation of Battery Energy Storage Systems (BESS) using a peak-shaving strategy to alleviate high-demand ...
    • On Measures of Uncertainty in Classification 

      Chlaily, Saloua; Ratha, Debanshu; Lozou, Pigi; Marinoni, Andrea (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-12)
      Uncertainty is unavoidable in classification tasks and might originate from data (e.g., due to noise or wrong labeling), or the model (e.g., due to erroneous assumptions, etc). Providing an assessment of uncertainty associated with each outcome is of paramount importance in assessing the reliability of classification algorithms, especially on unseen data. In this work, we propose two measures of ...
    • Simultaneous Global Ionospheric Disturbances Associated With Penetration Electric Fields During Intense and Minor Solar and Geomagnetic Disturbances 

      Zhang, Shun-Rong; Nishimura, Yukitoshi; Vierinen, Juha-Pekka; Lyons, Larry R.; Knipp, Delores J.; Gustavsson, Björn Johan; Waghule, Bhagyashree V.; Erickson, Philip J.; Coster, Anthea J.; Aa, Ercha; Spicher, Andres (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-29)
      A new observational phenomenon, named Simultaneous Global Ionospheric Density Disturbance (SGD), is identified in GNSS total electron content (TEC) data during periods of three typical geospace disturbances: a Coronal Mass Ejection-driven severe disturbance event, a high-speed stream event, and a minor disturbance day with a maximum Kp of 4. SGDs occur frequently on dayside and dawn sectors, with ...
    • The effect of a water-ice mantle on dust trajectories in the Kuiper belt 

      Gjelsvik, Amalie (Mastergradsoppgave; Master thesis, 2023-07-12)
      The New Horizons spacecraft has travelled through the Solar System and has reached a distance of 55 AU as of 2023. For one of the first times, the dust flux in the outer Solar System has been measured, using the instrument Student Dust Counter (SDC) onboard New Horizons. Between 30 and 50 AU is the Kuiper belt, which is a disk consisting of icy objects. These objects can undergo collisions, causing ...
    • A deep learning approach for anomaly identification in PZT sensors using point contact method 

      Kalimullah, Nur M M; Shelke, Amit; Habib, Anowarul (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-08-21)
      The implementation of piezoelectric sensors is degraded due to surface defects, delamination, and extreme weathering conditions, to mention a few. Hence, the sensor needs to be diagnosed before the efficacious implementation in the structural health monitoring (SHM) framework. To rescue the problem, a novel experimental method based on Coulomb coupling is utilised to visualise the evolution of ...
    • Investigating Spatial and Temporal Structuring of E-Region Coherent Scattering Regions Over Northern Norway 

      Huyghebaert, Devin Ray; Chau, Jorge L.; Spicher, Andres; Ivarsen, Magnus Fagernes; Clahsen, Matthias; Latteck, Ralph; Vierinen, Juha-Pekka (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-09-26)
      Recently, it has been shown that the Spread Spectrum Interferometric Multistatic meteor radar Observing Network radar system located in northern Norway is capable of measuring ionospheric E-region coherent scatter with spatial and temporal resolutions on the order of 1.5 km and 2 s, respectively. Four different events from June and July of 2022 are examined in the present study, where the coherent ...