Viser treff 680-699 av 942

    • Radar imaging with EISCAT 3D 

      Stamm, Johann; Vierinen, Juha; Urco, Juan M.; Gustavsson, Björn; Chau, Jorge L. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-04)
      A new incoherent scatter radar called EISCAT 3D is being constructed in northern Scandinavia. It will have the capability to produce volumetric images of ionospheric plasma parameters using aperture synthesis radar imaging. This study uses the current design of EISCAT 3D to explore the theoretical radar imaging performance when imaging electron density in the E region and compares numerical techniques ...
    • Radar observations of thermal plasma oscillations in the ionosphere 

      Vierinen, Juha; Gustavsson, Björn Johan; Hysell, David; Sulzer, M.; Perillat, Phil; Kudeki, Erhan (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-06-02)
      Incoherent scatter radar observations of ionospheric plasmas rely on echoes from electron density fluctuations with properties governed by the dispersion relations for ion acoustic and Langmuir waves. Radar observations of echoes associated with Langmuir waves (plasma lines) from thermal plasma are weak, and only a few near‐thermal level measurements have been reported. Plasma line echoes are typically ...
    • Radar size inference from statistics of RCS samples 

      Anfinsen, Stian Normann; Grydeland, Tom; Vierinen, Juha; Kastinen, Daniel; Ricker, Robert; Arntzen, Ingar M; Kero, J.; Høgda, Kjell Arild (Journal article; Tidsskriftartikkel; Peer reviewed, 2023)
      Radar Beam-park experiments have been very successful in characterizing the distribution of space debris objects, both in terms of orbital parameters but also in terms of limiting the estimates of their radar cross section, or RCS. A recent paper \[0\] used observed range and range rates to refine orbit estimates by matching up the observed SNR curve to that predicted by simulations. This gives good ...
    • Radar studies of ionospheric dust - plasma phenomena 

      Mann, Ingrid (Conference object; Konferansebidrag, 2018)
      Dust plasma phenomena occur in the Earth ionosphere in particular in the meteor ablation zone at altitudes ~50-95 km and above where radar meteors form. Radar also detect coherent polar mesospheric radar echoes (PME), i.e. radar echoes that are caused by spatial variations in the plasma refractive index at around 80 to 90 km altitude in the Earth’s mesosphere. During summer, PM(S)E form in the ...
    • Radar studies of ionospheric dusty plasma phenomena 

      Mann, Ingrid; Gunnarsdottir, Tinna; Häggström, Ingemar; Eren, Saliha; Tjulin, Anders; Myrvang, Margaretha; Rietveld, Mike T; Dalin, Peter; Jozwicki, Dorota; Trollvik, Henriette Marie Tveitnes (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-06-17)
      We discuss the influence of charged dust on radar observations in the Earth ionosphere. This region in the upper Earth atmosphere can be described as a partially ionized, low‐temperature plasma. Plasma parameters vary by orders of magnitude spatially and in time. Dust particles influence the charge balance, in some cases dusty plasma condition is met. The polar mesospheric echoes are an example of ...
    • Radio occultation observations of the solar corona over 1.60-1.86R⊙: Faraday rotation and frequency-shift analysis 

      Wexler, David; Hollweg, Joseph V; Efimov, Anatoli I; Song, Paul; Jensen, Elizabeth T; Lionello, Roberto; Vierinen, Juha; Coster, Anthea (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-09-02)
      The study of coronal energy transport, central to the solar wind acceleration problem, relies upon accurate representation of magnetic fields and plasma electron densities. This information is difficult to obtain in middle‐to‐lower coronal regions that may contain complex magnetic structures. Faraday rotation (FR) solar radio occultation observations, which reveal line‐of‐sight (LOS) integrated ...
    • Radiometric temperature reading of a hot ellipsoidal object inside the oral cavity by a shielded microwave antenna put flush to the cheek 

      Klemetsen, Øystein; Jacobsen, Svein Ketil; Birkelund, Yngve (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      A new scheme for detection of vesicoureteral reflux (VUR) in children has recently been proposed in the literature. The idea is to warm bladder urine via microwave exposure to at least fever temperatures and observe potential urine reflux from the bladder back to the kidney(s) by medical radiometry. As a preliminary step toward realization of this detection device, we present non-invasive temperature ...
    • Range-Doppler Mapping of Space-Based Targets Using the JRO 50 MHz Radar 

      Kesaraju, Saiveena; Mathews, J. D.; Milla, M.; Vierinen, Juha (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-02)
      The Jicamarca Radio Observatory (JRO) two-dimensional square array radar system operating at ~ 6-m wavelength was used to study the Moon and low Earth orbit satellites using the Range-Doppler inverse synthetic aperture radar technique also known as Delay-Doppler imaging. The radar data was collected on Oct 21, 2015. A circularly polarized coded pulse was transmitted from a quarter-array antenna ...
    • Ranking Using Transition Probabilities Learned from Multi-Attribute Data 

      Løkse, Sigurd; Jenssen, Robert (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-13)
      In this paper, as a novel approach, we learn Markov chain transition probabilities for ranking of multi-attribute data from the inherent structures in the data itself. The procedure is inspired by consensus clustering and exploits a suitable form of the PageRank algorithm. This is very much in the spirit of the original PageRank utilizing the hyperlink structure to learn such probabilities. ...
    • Rapid Colorimetric pH-Responsive Gold Nanocomposite Hydrogels for Sensing Applications 

      Salih, Ahmed E.; Elsherif, Mohamed; Alam, Fahad; Chiesa, Matteo; Butt, Haider (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-04-27)
      Surface functionalization of metallic nanoparticles (NPs) with external groups can be engineered to fabricate sensors that are responsive to various stimuli like temperature, pH, and numerous ions. Herein, we report the synthesis of gold nanoparticles (GNPs) functionalized with 3-mercaptopropionic acid (GNPs-MPA) and the doping of these nanoparticles into hydrogel materials using the ...
    • Rapid prototyping of 1xN multifocus gratings via additive direct laser writing 

      Reischke, Marie; Vanderpoorten, Oliver; Ströhl, Florian (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-04-05)
      Multifocus gratings (MFGs) enable microscopes and other imaging systems to record entire Z-stacks of images in a single camera exposure. The exact grating shape depends on microscope parameters like wavelength and magnification and defines the multiplexing onto a grid of MxN Z-slices. To facilitate the swift production and alteration of MFGs for a system and application at hand, we have developed ...
    • Rechargeable Iron-Ion Battery Using a Pure Ionic Liquid Electrolyte 

      Zhao, Yansong; Zhen, Yingpeng; Boström, Tobias Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-07-07)
      A rechargeable iron-ion battery (Fe-ion battery) has been fabricated in our laboratory using a pure ionic liquid electrolyte. Magnetic ionic liquids of 1-butyl-3-methylimidazolium tetrachloroferrate (BmimFeCl<sub>4</sub>) and 1-methyl-3-octylimidazolium tetrachloroferrate (OmimFeCl<sub>4</sub>) are synthesized and utilized as electrolytes in this work. The chemical structure of the two ionic ...
    • Reconsidering Representation Alignment for Multi-View Clustering 

      Trosten, Daniel Johansen; Løkse, Sigurd Eivindson; Jenssen, Robert; Kampffmeyer, Michael (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-13)
      Aligning distributions of view representations is a core component of today’s state of the art models for deep multi-view clustering. However, we identify several drawbacks with naïvely aligning representation distributions. We demonstrate that these drawbacks both lead to less separable clusters in the representation space, and inhibit the model’s ability to prioritize views. Based on these ...
    • Reconstructing force profiles with an amplitude-modulation AFM in tapping mode 

      Olukan, Tuza Adeyemi; Lai, Chia-Yun; Santos, Sergio; Amadei, Carlo Alberto; Chiesa, Matteo (Research report; Forskningsrapport, 2020-07)
      Here we demonstrate how to reconstruct force profiles with an amplitude-modulation AFM operated in in standard tapping mode. Our example is based on the Cypher scanning probe microscope from Asylum Research. The method is based on Sader and Katan’s algorithm, but we have implemented an experimental set-up that allows for robust reconstruction. We discuss the details here.
    • Reconstruction of intermittent time series as a superposition of pulses 

      Ahmed, Sajidah; Garcia, Odd Erik; Theodorsen, Audun (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-05)
      Fluctuations in a vast range of physical systems can be described as a superposition of uncorrelated pulses with a fixed shape, a process commonly referred to as a (generalized) shot noise or a filtered Poisson process. In this paper, we present a systematic study of a deconvolution method to estimate the arrival times and amplitudes of the pulses from realizations of such processes. The method shows ...
    • Reconstruction of precipitating electrons and three-dimensional structure of a pulsating auroral patch from monochromatic auroral images obtained from multiple observation points 

      Fukizawa, Mizuki; Sakanoi, Takeshi; Tanaka, Yoshimasa; Ogawa, Yasunobu; Hosokawa, Keisuke; Gustavsson, Björn Johan; Kauristie, Kirsti; Kozlovsky, Alexander; Raita, Tero; Brändström, Urban; Sergienko, Tima (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-07-12)
      In recent years, aurora observation networks using high-sensitivity cameras have been developed in the polar regions. These networks allow dimmer auroras, such as pulsating auroras (PsAs), to be observed with a high signal-to-noise ratio. We reconstructed the horizontal distribution of precipitating electrons using computed tomography with monochromatic PsA images obtained from three observation ...
    • 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 ...
    • The red-sky enigma over Svalbard in December 2002 

      Sigernes, F.; Shumilov, N.; Lloyd, N.; Havnes, O.; Lorentzen, D.A.; Neuber, R.; Hoppe, Ulf-Peter; Degenstein, D.; Moen, J.; Gjessing, Y.; Skartveit, A.; Raustein, E.; Ørbæk, J.B.; Deehr, C.S. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-07-27)
      On 6 December 2002, during winter darkness, an extraordinary event occurred in the sky, as viewed from Longyearbyen (78° N, 15° E), Svalbard, Norway. At 07:30 UT the southeast sky was surprisingly lit up in a deep red colour. The light increased in intensity and spread out across the sky, and at 10:00 UT the illumination was observed to reach the zenith. The event died out at about 12:30 UT. Spectral ...
    • 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 ...
    • Reinforced Auto-Zoom Net: Towards Accurate and Fast Breast Cancer Segmentation in Whole-Slide Images 

      Dong, Nanqing; Kampffmeyer, Michael C.; Liang, Xiaodan; Wang, Zeya; Dai, Wei; Xing, Eric P. (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-20)
      Convolutional neural networks have led to significant breakthroughs in the domain of medical image analysis. However, the task of breast cancer segmentation in whole-slide images (WSIs) is still underexplored. WSIs are large histopathological images with extremely high resolution. Constrained by the hardware and field of view, using high-magnification patches can slow down the inference process and ...