Blar i utgivelsesdato Institutt for fysikk og teknologi

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    • An imaging interferometry capability for the EISCAT Svalbard Radar. 

      Grydeland, Tom; Chau, J.L.; La Hoz, C.; Brekke, Asgeir (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-01-31)
      Interferometric imaging (aperture synthesis imaging) is a technique used by radio astronomers to achieve angular resolution that far surpasses what is possible with a single large aperture. A similar technique has been used for radar imaging studies of equatorial ionospheric phenomena at the Jicamarca Radio Observatory. We present plans for adding an interferometric imaging capability to the ...

    • The harmonizable representation of complex-valued nonstationary random processes 

      Hindberg, Heidi (Master thesis; Mastergradsoppgave, 2005-06-14)
      In this thesis we study the second-order statistical moment functions that characterizes complex-valued harmonizable processes. A real-valued harmonizable process has four Hermitian second-order functions. These functions are equivalent representations of the second-order statistical quantities of the process. For a complex-valued harmonizable process, however, we need the complementary functions ...

    • 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 ...

    • Relative drift between black aurora and the ionospheric plasma. 

      Blixt, Erik Mårten; Kosch, M.J.; Semeter, J. (Journal article; Tidsskriftartikkel, 2005-07-27)
      Black auroras are recognized as spatially well-defined regions within uniform diffuse aurora where the optical emission is significantly reduced. Although a well studied phenomenon, there is no generally accepted theory for black auroras. One theory suggests that black regions are formed when energetic magnetospheric electrons no longer have access to the loss cone. If this blocking mechanism drifts ...

    • The electron energy distribution during HF pumping, a picture painted with all colors. 

      Rietveld, Michael T.; Gustavsson, B.; Sergienko, T.; Grydeland, Tom; La Hoz, Cesar; Kosch, M.J.; Brändström, B.U.E.; Leyser, T.B.; Isham, B.; Gallop, P.; Aso, T.; Ejiri, M.; Steen, A.; Kaila, K.; Jussila, J.; Holma, H. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-07-28)
      The shape of the electron energy distribution has long been a central question in the field of highfrequency radio-induced optical emission experiments. This report presents estimates of the electron energy distribution function, fe(E), from 0 to 60 eV, based on optical multiwavelength (6300, 5577, 8446, 4278 A° ) data and 930-MHz incoherent scatter radar measurements of ion temperature, electron ...

    • Solar Wind from Coronal Funnels and Transition Region Lyalpha 

      Esser, Ruth; Lie-Svendsen, Øystein; Janse, Åse Marit; Killie, Mari Anne (Journal article; Tidsskriftartikkel; Peer reviewed, 2005-08-10)
      Using a newly developed gyrotropic solar wind model that extends continuously from the mid-chromosphere to 1 AU and that accounts for radiative losses in the transition region, we have studied the difference between the fast solar wind emanating from a funnel geometry and a ``traditional'' rapidly expanding wind. The main aim is to determine whether or not observations of the Lyalpha intensity in ...

    • The effect of electron bite-outs on artificial electron heating and the PMSE overshoot. 

      Belova, E.; Kassa, M.; Havnes, O. (Journal article; Peer reviewed; Tidsskriftartikkel, 2005-12-23)
      We have considered the effect that a local reduction in the electron density (an electron bite-out), caused by electron absorption on to dust particles, can have on the artificial electron heating in the height region between 80 to 90 km, where noctilucent clouds (NLC) and the radar phenomenon PMSE (Polar Mesospheric Summer Echoes) are observed. With an electron density profile without ...

    • Mikrobølgeradiometri anvendt til deteksjon av temperaturgradienter i brystvevsfantom 

      Klemetsen, Øystein (Master thesis; Mastergradsoppgave, 2006-06-01)
      En passiv, ikke-invasiv og ufarlig metode for detektering av brystkreft er motivasjonen for denne oppgaven. Basisen for mikrobølgeteori og radiometrisk teori er presentert. Videre presenteres grunnlaget for å kunne foreta passive målinger på brystvevsmodeller, målemetoder og forbedringsmuligheter innen mikrobølge radiometri. Vi studerer ulike forbedringsmuligheter ved å se på systemet ved Institutt ...

    • Statistical modelling of polarimetric SAR data 

      Doulgeris, Anthony Paul (Master thesis; Mastergradsoppgave, 2006-06-02)
      A statistical modelling technique is developed to analyse polarimetric synthetic aperture radar (PolSAR) images. Polarimetric SAR data consists of four complex scattering coefficients at each image location, requiring multivariate modelling techniques, and this work focuses on a simple class of multivariate distributions, the scale mixture of Gaussians. Three parametric model families of that ...

    • Low-frequency noise power spectrum density characterizing of SiGe HBTs 

      Qi, Peng (Master thesis; Mastergradsoppgave, 2006-06-06)
      The main purposes of this thesis are the Low-Frequency Noise measurement of Silicon-Germanium Heterojunction Bipolar Transistors and its Power Spectrum Density Characterizing. The new generation 375 GHZ SiGe HBTs were measured in this work. We show that most of PSDs of the new generation SiGe HBTs have very ”bumpy” spectra which is contributed by GR noise sources. We investigated their basic ...

    • Directional features of the downshifted peak observed in HF-induced stimulated electromagnetic emission spectra obtained using an interferometer. 

      Rietveld, Michael T.; Tereshchenko, E.D.; Belyey, Vasyl; Yurik, R.Yu; Brekke, Asgeir; Khudukon, B.Z.; Isham, B.; Hagfors, T.; Grill, M. (Journal article; Peer reviewed; Tidsskriftartikkel, 2006-08-09)
      A high frequency (HF) ionospheric modification experiment was carried out between 25 September and 8 October 2004, using the EISCAT HF transmitter located near Tromsø, Norway. During this experiment the spectra of the stimulated HF sideband waves (stimulated electromagnetic emission or SEE) induced by the HF pump were observed using an interferometer consisting of three spaced receiving antennas ...

    • Phase calibration of the EISCAT Svalbard Radar interferometer using optical satellite signatures. 

      Grydeland, Tom; Sullivan, J.M.; Blixt, Erik Mårten; Ivchenko, N.; Lockwood, M.; Lanchester, B.S. (Journal article; Peer reviewed; Tidsskriftartikkel, 2006-09-20)
      The link between natural ion-line enhancements in radar spectra and auroral activity has been the subject of recent studies but conclusions have been limited by the spatial and temporal resolution previously available. The next challenge is to use shorter sub-second integration times in combination with interferometric programmes to resolve spatial structure within the main radar beam, and so ...

    • Winter warmings, tides and planetary waves. Comparisions between CMAM (with interactive chemistry) and MFR-MetO observations and data. 

      Manson, A.H.; Hall, Chris; Meek, C.; Chshyolkova, T.; McLandress, C.; Avery, S.K.; Fritts, D.C.; Hocking, W.K.; Igarashi, K.; MacDougall, J.W.; Murayama, Y.; Riggin, D.C.; Thorsen, D.; Vincent, R.A. (Journal article; Peer reviewed; Tidsskriftartikkel, 2006-10-20)
      Following earlier comparisons using the Canadian Middle Atmosphere Model (CMAM, without interactive chemistry), the dynamical characteristics of the model are assessed with interactive chemistry activated. Time-sequences of temperatures and winds at Tromsø (70° N) show that the model has more frequent and earlier stratospheric winter warmings than typically observed. Wavelets at mesospheric heights ...

    • The relationship between small-scale and large-scale ionospheric electron density irregularities generated by powerful HF electromagnetic waves at high latitudes 

      Rietveld, Michael T.; Tereshcenko, E.D.; Khudukon, B.Z.; Brekke, Asgeir; Isham, B.; Hagfors, T. (Journal article; Tidsskriftartikkel; Peer reviewed, 2006-11-21)
      Satellite radio beacons were used in June 2001 to probe the ionosphere modified by a radio beam produced by the EISCAT high-power, high-frequency (HF) transmitter located near Tromsø (Norway). Amplitude scintillations and variations of the phase of 150- and 400-MHz signals from Russian navigational satellites passing over the modified region were observed at three receiver sites. In several papers ...

    • Particle precipitations during NEIAL events : simultaneous ground based observations at Svalbard 

      Lorentzen, Dag Arne; Lunde, June; Gustavsson, B; Ogawa, Y; Løvhaug, U.P.; Ogawa, Yasunobu (Journal article; Tidsskriftartikkel; Peer reviewed, 2007)
      In this paper we present Naturally Enhanced Ion Acoustic Lines (NEIALs) observed with the EISCAT Svalbard Radar (ESR). For the first time, long sequences of NEIALs are recorded, with more than 50 events within an hour, ranging from 6.4 to 140 s in duration. The events took place from ~08:45 to 10:00 UT, 22 January 2004. We combine ESR data with observations of optical aurora by a meridian scanning ...

    • On the secondary charging effects and structure of mesospheric dust particles impacting on rocket probes 

      Havnes, Ove; Næsheim, Lars Irgens (Journal article; Tidsskriftartikkel; Peer reviewed, 2007)

    • Dataverktøy til regning, skriving og tegning i naturfag 

      Haugland, Ole Anton (Book; Bok, 2007)

    • Dielectric microsphere manipulation and chain assembly by counter-propagating waves in a channel waveguide 

      Grujic, Katarina; Hellesø, Olav Gaute (Journal article; Tidsskriftartikkel; Peer reviewed, 2007)

    • Spatial scaling of optical fluctuations during substorm-time aurora 

      Kozelov, Boris V; Rypdal, Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2007)

    • Stretched exponential relaxation and ac universality in disordered dielectrics 

      Rasmussen, Jens Juul; Milovanov, Alexander V.; Rypdal, Kristoffer (Working paper; Arbeidsnotat, 2007-05-30)
      This paper is concerned with the connection between the properties of dielectric relaxation and ac (alternating-current) conduction in disordered dielectrics. The discussion is divided between the classical linear-response theory and a self-consistent dynamical modeling. The key issues are, stretched exponential character of dielectric relaxation, power-law power spectral density, and anomalous ...