Institutt for fysikk og teknologi: Nye registreringer

Viser treff 1341-1360 av 1428

    • Simulations of plasma filament dynamics in toroidal geometry 

      Rønningen, Petter (Master thesis; Mastergradsoppgave, 2010-05-18)
      Interchange driven propagation of so-called "blobs" arises in basic laboratory plasmas, in the scrape-off layer of fusion plasmas and as Equatorial Spread-F (ESF) phenomena. The propagation of such blobs has been demonstrated in the VTF experiment at MIT and in earlier simulations. Experimental results show that the velocity of these blobs is inverse proportional to the neutral gas pressure. These ...

    • Numerical studies of radial filament motion in toroidally confined plasmas 

      Kube, Ralph (Master thesis; Mastergradsoppgave, 2010-05)
      Numerical studies of radial filament motions in the SOL of toroidally confined plasmas are studies. We use a two dimensional two-field model to characterize blob-like structures in the radial-poloidal domain. These structures are observed to achieve velocities in the order of the ion acoustic velocity in the SOL of tokamaks and other toroidal confinement devices. By numerical means we find a ...

    • Review and test of funnel shape geometries in solar wind acceleration 

      Trollebø, Robert (Master thesis; Mastergradsoppgave, 2009-12-15)
      The origin and heating of the solar wind is still a puzzle. We review in this study the idea that the solar wind originates in coronal funnels. We place emphasis on the fast solar wind. This study provides primarily a historic overview over the development of the idea of funnel expansion. We present examples of recent solar wind studies that investigate the funnel geometry. These studies include ...

    • On the relationship between auroral absorption, electrojet currents and plasma convection 

      Hansen, Truls Lynne; Kellerman, A. C.; Makarevich, R. A.; Honary, F. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009-02-02)
      In this study, the relationship between auroral absorption, electrojet currents, and ionospheric plasma convection velocity is investigated using a series of new methods where temporal correlations are calculated and analysed for different events and MLT sectors. We employ cosmic noise absorption (CNA) observations obtained by the Imaging Riometer for Ionospheric Studies (IRIS) system in ...

    • Climatic trends in E-region critical frequency and virtual height above Tromsø (70 degrees N, 10 degrees E) 

      Cannon, P. S.; Hall, Chris; Brekke, Asgeir (Journal article; Tidsskriftartikkel; Peer reviewed, 2007-11-29)
      We have examined the long time series of observations of E-region virtual height (1948–2006) and critical frequency (1935-2006) hitherto made by the Tromsø ionosonde at 70 degrees N, 19 degrees E. Combining a simplistic trend analysis with a rigorous treatment of errors we identify a negative trend in critical frequency. While a similar analysis of the virtual height h'E also suggests a negative ...

    • Phenomena induced by powerful HF pumping towards magnetic zenith with a frequency near the F-region critical frequency and the third electron gyro harmonic frequency 

      Brekke, Asgeir; Blagoveshchenskaya, N. F.; Carlson, H. C.; Kornienko, V. A.; Borisova, T. D.; Rietveld, M. T.; Yeoman, T. K. (Journal article; Tidsskriftartikkel; Peer reviewed, 2009-01-08)
      Multi-instrument observational data from an experiment on 13 October 2006 at the EISCAT/HEATING facility at Tromsø, Norway are analysed. The experiment was carried out in the evening hours when the electron density in the F-region dropped, and the HF pump frequency fH was near and then above the critical frequency of the F2 layer. The distinctive feature of this experiment is that the pump frequency ...

    • Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance 

      Brekke, Asgeir; Oyama, S; Watkins, B. J.; Maeda, S.; Shinagawa, H.; Nozawa, S.; Ogawa, Y.; Lathuillere, C.; Kofman, W. (Journal article; Tidsskriftartikkel; Peer reviewed, 2008-06-11)
      Lower-thermospheric winds at high latitudes during moderately-disturbed geomagnetic conditions were studied using data obtained with the European Incoherent Scatter (EISCAT) Kiruna-Sodankylä-Tromsø (KST) ultrahigh frequency (UHF) radar system on 9–10 September 2004. The antenna-beam configuration was newly designed to minimize the estimated measurement error of the vertical neutralwind speed in the ...

    • A multiwavelet approach to the direct solution of the Poisson equation: implementation and optimization 

      Jensen, Stig Rune (Master thesis; Mastergradsoppgave, 2009-11-15)
      This work is presenting a fully numerical approach for the direct solution of the Poisson equation for the electrostatic potential given by an arbitrary charge density. Efficient solution of this equation is important in many fields of science, where the current work is dealing with nuclear and electronic potential calculations, used in the field of computational chemistry. The equation is solved ...

    • Dataverktøy til regning, skriving og tegning i naturfag 

      Haugland, Ole Anton (Book; Bok, 2007)

    • Fysikk i den polare atmosfæren og nordlyset 

      Brekke, Asgeir (Research report; Forskningsrapport, 2008)
      Den polare atmosfæren har fått mer oppmerksomhet i den senere tid enn den vanligvis har vært forunt. Dette henger sammen med tanken om at den er så ren og upåvirket av eventuelle forurensninger som vi pumper ut i atmosfæren i de mer urbane strøk. Dersom atmosfæren tar skade av denne aktiviteten, forventer en å se skadevirkningene først og klarest i den polare atmosfæren. Svekkelsen av ozonlaget ...

    • Three photometric methods tested on ground-based data of Q 2237+0305 

      Burud, I.; Østensen, R.; Stabell, R.; Magain, P.; Courbin, F.; Refsda, S.; Remy, M.; Teuber, J. (Journal article; Tidsskriftartikkel; Peer reviewed, 1998-09-09)
      The Einstein Cross, Q 2237+0305, has been photometrically observed in four bands on two successive nights at NOT (La Palma, Spain) in October 1995. Three independent algorithms have been used to analyse the data: an automatic image decomposition technique, a CLEAN algorithm and the new MCS deconvolution code. The photometric and astrometric results obtained with the three methods are presented. ...

    • Burst statistics of fluctuations in a simple magnetized torus configuration 

      Rypdal, Kristoffer; Živkovic, Tatjana; Østvand, Lene (Working paper; Arbeidsnotat, 2009-04-19)
      In a toroidal plasma confined by a purely toroidal magnetic field the plasma transport is governed by electrostatic turbulence driven by the flute interchange instability on the low-field side of the torus cross section. In this paper we revisit experimental data obtained from the Blaamann torus at the University of Tromso. On time-scales shorter than the poloidal rotation time, the time series of ...

    • Design, implementering og evaluering av et trådløst medisinsk radiometer basert på IEEE 802.15.4-standarden og Zigbee. 

      Johansen, Amund Kronen (Master thesis; Mastergradsoppgave, 2009-06-01)
      Brystkreft er den vanligste kreftformen for kvinner og overlevelsesraten er betydelig høyere ved tidlig deteksjon. De vanligste undersøkelsesmetodene (mammografi, ultralyd, MRI) er basert på aktive metoder som medfører en viss strålingsfare. Et enkelt, ikke-invasivt instrument som baserer seg på passive metoder er derfor motivasjonen for denne masteroppgaven. Oppgaven beskriver en konseptuell ...

    • Optisk resonans i mikrokuler av glass med høy brytningsindeks 

      Husabø, Bjarne Janson (Master thesis; Mastergradsoppgave, 2009-06-15)
      I denne oppgaven har vi sett på effekten av lys som kobles fra en bølgeleder inn i optiske mikrokuler av høyindeksglass. Vi har studert Q-faktorer, og funnet at disse er lavere for kuler omgitt av vann enn tørre kuler, men at forskjellen er mindre enn mellom individuelle kuler. Vi har observert høyere ordens resonanser i kuler med større diameter. Vi har også forsøkt å utnytte resonans til å flytte ...

    • Monostatisk antennearray for UWB radar 

      Andersen, Rolf (Master thesis; Mastergradsoppgave, 2009-06)
      Ultrabredbåndet (ultrawideband - UWB) radar brukt til deteksjon av bryst-kreft viser oppløftende resultater på grunn av dens gode romlige oppløsning og dype penetreringsdybde. Bakgrunnen for å bruke UWB-radar til dette formålet er kontrasten mellom de dielektriske egenskapene til friskt brystvev og en kreftsvulst. Noe som vil føre til relativt mye reflektert energi fra kreftsvulsten. En av utfordringene ...

    • Estimering av dempingskoeffisienter i elastiske materialer ved hjelp av bredbåndet ultralyd 

      Ali, Josoph Abuker (Master thesis; Mastergradsoppgave, 2009-07-01)
      Dette er en eksperimentell oppgave der et bredbåndet ultralydsystem er brukt til å undersøke hvordan dempingen av ultralydbølger i elastiske materialer, avhenger av frekvensen. For å gjøre denne undersøkelsen ble det utviklet en holder i pleksiglass med en ultralydtransduser på hver side. I denne holderen kan prøver av ulike materialer lett festes og undersøkes ved at holderen plasseres i et vannbad. ...

    • Self-similar transport processes in a two-dimensional realization of multiscale magnetic field turbulence 

      Chiaravalloti, Francesco; Milovanov, Alexander V.; Zimbardo, Gaetano (Journal article; Tidsskriftartikkel; Peer reviewed, 2004-12-14)
      We present the results of a numerical investigation of charged-particle transport across a synthesized magnetic configuration composed of a constant homogeneous background field and a multiscale perturbation component simulating an effect of turbulence on the microscopic particle dynamics. Our main goal is to analyze the dispersion of ideal test particles faced to diverse conditions in the turbulent ...

    • Electron fishbones: theory and experimental evidence 

      Milovanov, Alexander V.; Zonca, F.; Buratti, P.; Cardinali, A.; Chen, L.; Dong, J.-Q.; Long, Y.-X.; Romanelli, F.; Smeulders, P.; Wang, L.; Wang, Z.-T.; Castaldo, C.; Cesario, R.; Giovannozzi, E.; Marinucci, M.; Ridolfini, V. Pericoli (Journal article; Tidsskriftartikkel; Peer reviewed, 2007-07-19)
      We discuss the processes underlying the excitation of fishbone-like internal kink instabilities driven by supra-thermal electrons generated experimentally by different means: Electron Cyclotron Resonance Heating (ECRH) and by Lower Hybrid (LH) power injection. The peculiarity and interest of exciting these electron fishbones by ECRH only or by LH only is also analyzed. Not only the mode stability ...

    • The WSO, a world-class observatory for the ultraviolet 

      Solheim, Jan Erik; Barstow, M.A.; Binette, L.; Brosch, N.; Cheng, F-Z.; Dennefeld, M.; Gomez de Castro, A.I.; Haubold, H.; van der Hucht, K.A.; Kappelmann, N.; Martinez, P.; Ribak, E.N.; Moisheev, A.; Pagano, I.; Sahade, J.; Wamsteker, W.; Werner, K.; Becker-Ross, H.; Florek, S.; Shustov, B. (Conference object; Konferansebidrag, 2002-09-17)
      The World Space Observatory is an unconventional space project proceeding via distributed studies. The present design, verified for feasibilty, consists of a 1.7-meter telescope operating at the second Largangian point of the Earth-Sun system. The focal plane instruments consist of three UV spectrometers covering the spectral band from Lyman alpha to the atmospheric cutoff with R~55,000 and offering ...

    • HS 0705+6700: a new eclipsing sdB binary 

      Østensen, R.; Solheim, Jan Erik; Johannessen, F. (Journal article; Tidsskriftartikkel, 2001-10-09)
      We report the discovery of an eclipsing binary – HS 0705+6700 – being an sdB star with a faint companion. From its light curve the orbital period of 8263.87 s, the mass ratio of the system q = 0.28, the inclination of 84.◦4 and other system parameters are derived. The companion does not contribute to the optical light of the system except through a strong reflection effect. The semiamplitude of ...