Mastergradsoppgaver i fysikk

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Mastergradsoppgaver i fysikk

The collection contains 20 document(s)

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• Suppression of fingering instabilities in superconductors by magnetic braking

  Lator, Elijah (Master thesis; Mastergradsoppgave, Nov-2012)

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  Abstract:	Superconductors are materials that can transport electric current without resistance and loss of energy at low temperature. This thesis is a theoretical investigation problem about the thermomagnetic instability in superconductor and its suppression by deposing a metallic layer.
  URI:	http://hdl.handle.net/10037/4779

  File(s) in this item: 1

  thesis.pdf   (1.311Mb)
• Drift wave turbulence and zonal flows

  Meyer, Ole Hauke Heinz (Master thesis; Mastergradsoppgave, 15-Nov-2012)

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  Abstract:

  Anomalously large radial transport levels in fusion devices is commonly believed to be the cause of small-scale edge localized electrostatic drift wave turbulence. We review the basic drift wave instability mechanism and show how poloidally elongated structures can self-consistently emerge from the small-scale turbulent motions through envelope modulation governed by the cubic nonlinear Schrödinger equation. There has been extensive study of the zonal flow - drift wave system recently, showing that zonal structures effectively reduce radial transport levels. We study the drift wave turbulence model due to Hasegawa and Wakatani (OHW), which upon subtle modification (MHW) also allows for zonal flow formation which is characteristic for the edge region of fusion devices. There is experimental evi- dence of long-range correlations; we investigate whether zonal flows give rise to such behavior in the hydrodynamic and quasi-adiabatic state of the OHW and MHW models. Rescaled range analysis gives no indication of long-range correlation. Struc- ture function analysis confirm this finding for the zonal flow free simulations where fluctuations are essentially Gaussian. Heavy tails in probability distributions of tur- bulent quantities due to the emergence of zonal flows in the quasi-adiabatic state of MHW complicate the analysis and increase in self-similarity parameters computed from structure functions cannot be used as proof for long-range correlation. The finding of this work is that significantly longer time-series are needed to clarify whether long-range correlations are an artefact of zonal structures or not.

  URI:

  http://hdl.handle.net/10037/4778

  File(s) in this item: 1

  thesis.pdf   (24.64Mb)
• Spectral analysis of radar coherent echoes and its relation to turbulence

  Pokhrel, Marshal (Master thesis; Mastergradsoppgave, Nov-2012)

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  Abstract:

  The measurements of polar mesosphere summer echoes has been performed since a long time by the ground based techniques with EISCAT VHF and UHF radar system and recently with MORRO. Based on these observation, my thesis is focussed on the data obtained from manda program to get data from EISCAT 3D demonstrator antenna array in Kiruna that receives from EISCAT VHF transmitter here from Tromso in the year July 2011 to analyse the Polar Mesospheric Summer Echoes(PMSE). The thesis starts with the data analysis of the PMSE observing its parameters like spectral width, doppler shift and amplitude. These parameters are built in a profile and plotted as a function of time and height. In addition, the widely accepted fact of the dependence of PMSE with turbulence is shown in the thesis which is made by showing the profiles of dissipation rate as a function of height and time. Focus is made on calculation of spectral width and its variations with height in different times. In addition , the dissipation rate has been depicted and the physics underlying beneath it has been explained.

  URI:

  http://hdl.handle.net/10037/4642

  File(s) in this item: 1

  thesis.pdf   (2.843Mb)
• Studies of plasma potential with emissive probes in the low temperature plasma experiment NJORD

  Schregel, Christian-Georg (Master thesis; Mastergradsoppgave, 02-Nov-2012)

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  Abstract:

  In this thesis, the concept of an emissive probe has been used to obtain the plasma potential in the low temperature plasma experiment NJORD. An emissive probe is a probe concept in which a wire is heated strong enough to emit a Richardson current. The probe is then swept through several voltage biases and thus, an I-V trace obtained. With the current from the emission and the collected current, this gives in principle very easy access to the plasma potential. NJORD is a plasma discharge driven by a radio frequency in what is called helicon range. This specifies a small frequency band of oscillations that connect well to the electrons. While having good heating properties, it induces a set of problems for the emissive probe due to the oscillations. Applying modelling and monitoring how the recorded traces deviate from the expected ideal traces, however, gives some insight into the physical processes taking place and made it possible to prove the existence of a second electron population. Observing two electron populations with this concept is a novelty and could help completing the theory behind the so called "helicon double layer thruster" concept.

  URI:

  http://hdl.handle.net/10037/4639

  File(s) in this item: 1

  thesis.pdf   (8.253Mb)
• Multi-sensor data fusion and feature extraction for forest applications

  Yitayew, Temesgen Gebrie (Mastergradsoppgave; Master thesis, 15-May-2012)

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  Abstract:

  The purpose of this study was to extract, evaluate and select different multi-frequency polarimetric SAR and multi-spectral optical features to demonstrate the benefit of multi-sensor data fusion for forest applications. Multi-frequency fully Polarimetric SAR data at P-, L- and C-band and multi-spectral Landsat TM data acquired over the Nezer forest in France were used for demonstration. The scene is composed of homogeneous fields of either bare soil or maritime pine trees of different ages, and the application was discriminating the bare soil, and the trees in terms of their ages. A total of twenty-six features; six from each of the three Polarimetric SAR datasets and eight from the optical dataset were extracted. Significant classification accuracy improvement (up to 12%) was achieved by fusing SAR and optical datasets. Therefore, attention should be given to the combined use of them whenever they are available. Five features were found to jointly preserve 98.5% of the classification information of the available set. In addition to retaining most of the valuable information, these few identified features were found useful to interpret the scene in terms of the different forest scattering mechanisms. Therefore, they can be reasonably expected to be used for other forest applications too.

  URI:

  http://hdl.handle.net/10037/4609

  File(s) in this item: 1

  thesis.pdf   (5.828Mb)

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