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norskInstitutt for fysikk og teknologi: Recent submissions
Now showing items 1101-1120 of 1407
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Investigations of ionospheric disturbances using coherent HF instrumentation
(Master thesis; Mastergradsoppgave, 2016-05-15)This work is based on long term monitoring the HF signal data at 9.996 MHz at mid-latitudes from the short radio-path Moscow-Kharkiv and at high-latitudes from the longer radio-path Moscow-Tromso for 2013. The HF signal transmitter is the radio station RWM in Moscow, Russia. The receiver stations are located in Tromso (Norway) and Kharkiv (Ukraine). Using intensity and the Doppler frequency shift ... -
Investigation of the ion composition in the topside ionosphere at solar maximum using incoherent scatter technique
(Master thesis; Mastergradsoppgave, 2016-05-15)The aim of this study was to investigate the altitudinal and diurnal variations of light ion densities in the topside ionosphere during the 23rd and 24th solar maximums. This made it possible to understand the behavior of the ion composition after extended solar minimum and compare how it differs from the preceding solar maximum. The observed variations are compared with estimates of empirical (IRI) ... -
Arctic Cirrus Clouds: A Comparison of Properties Derived from Measurements by Ground-Based and Spaceborne Lidar Systems
(Master thesis; Mastergradsoppgave, 2015-12-15)The purpose of this thesis is to investigate Arctic cirrus clouds. In this work, data from the ground-based lidar system at ALOMAR, Andøya Space Center. and the spaceborne lidar onboard the CALIPSO satellite is used. Cirrus clouds are an important factor in modeling climate changes, which is one of the major research fields of this time. Most of the cirrus cloud research concentrates on investigating ... -
Super-Resolution Imaging of Sub-Mitochondrial Structures using Structured Illumination Microscopy
(Master thesis; Mastergradsoppgave, 2016-05-15)Modern science is based on observation, and its advances are limited by what is possible to observe. For centuries optical microscopy was limited by the diffraction of light, making structures closer together than half the wavelength of light unresolvable. In recent years, the new field of optical nanoscopy has emerged, enabling diffraction-limited structures to be resolved. As opposed to ... -
Auto-correlation function and frequency spectrum due to a super-position of uncorrelated exponential pulses
(Peer reviewed; Journal article; Tidsskriftsartikkel, 2017-03)The auto-correlation function and the frequency power spectral density due to a super-position of uncorrelated exponential pulses are considered. These are shown to be independent of the degree of pulse overlap and thereby the intermittency of the stochastic process. For constant pulse duration and a one-sided exponential pulse shape, the power spectral density has a Lorentzian shape which is flat ... -
Power law spectra and intermittent fluctuations due to uncorrelated Lorentzian pulses
(Peer reviewed; Journal article; Tidsskriftsartikkel, 2017-02)A stochastic model for intermittent fluctuations due to a super-position of uncorrelated Lorentzian pulses is presented. For a constant pulse duration, this is shown to result in an exponential power spectral density for the stationary process. A random distribution of pulse durations modifies the frequency spectrum, and several examples are shown to result in power law spectra. The distribution of ... -
Modification of the high-latitude ionospheric F region by high-power HF radio waves at frequencies near the fifth and sixth electron gyroharmonics
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-02-01)We study the modification effects of the high-latitude ionospheric F region induced by a highpower O-mode HF radio wave injected towards the magnetic zenith, at frequencies near the fifth and sixth electron gyroharmonics using the EISCAT/Heating facility. Multi-instrument diagnostics with the EISCAT incoherent scatter radar (930 MHz) at Tromsø, Norway, the CUTLASS coherent radar at Hankasalmi, ... -
The behavior of electron density and temperature during ionospheric heating near the fifth electron gyrofrequency
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-01-27)The experimental phenomena involving the changes in electron temperature and electron density as a function of pump frequency during an ionospheric heating campaign at European Incoherent Scatter near Tromsø, Norway, are reported. When the pump frequency is slightly above the fifth electron gyrofrequency, the UHF radar observation shows some apparent enhancements over a wide altitude range in radar ... -
A solvable blob-model for magnetized plasmas
(Peer reviewed; Journal article; Tidsskriftsartikkel, 2016-09-06)A simple analytically solvable model for blobs in magnetized plasmas is proposed. The model gives results for a scaling of the blob velocity with the amplitude of the density perturbation. Limiting cases are considered: one where the plasma motion is strictly perpendicular to an externally imposed toroidal magnetic field, and one where the electrons can move along magnetic field lines to compensate ... -
Fluctuation statistics in the scrape-off layer of Alcator C-Mod
(Peer reviewed; Journal article; Tidsskriftsartikkel, 2016-03-30)We study long time series of the ion saturation current and floating potential, sampled by Langmuir probes dwelled in the outboard mid-plane scrape-off layer and embedded in the lower divertor baffle of Alcator C-Mod. A series of ohmically heated L-mode plasma discharges is investigated with line-averaged plasma density ranging from ${{\bar{n}}_{\text{e}}}/{{n}_{\text{G}}}=0.15$ to 0.42, where n G ... -
New capabilities of the upgraded EISCAT high-power HF facility
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-09-22)The high-power HF (high-frequency) facility (commonly known as Heating) near Tromsø, Norway, which is an essential part of the European Incoherent Scatter Scientific Association, has been upgraded in certain key areas in recent years. It is one of only four similar facilities in the world operating at present. An updated description of the facility is given, together with scientific motivation and ... -
Nanoscopy of bacterial cells immobilized by holographic optical tweezers
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-12-13)Imaging non-adherent cells by super-resolution far-field fluorescence microscopy is currently not possible because of their rapid movement while in suspension. Holographic optical tweezers (HOTs) enable the ability to freely control the number and position of optical traps, thus facilitating the unrestricted manipulation of cells in a volume around the focal plane. Here we show that immobilizing ... -
Oil spill characterization in the hybrid-polarity SAR domain using log-cumulants
(Peer reviewed; Journal article; Tidsskriftsartikkel, 2016-10-18)Log-cumulants have proven to be an interesting tool for evaluating the statistical properties of potential oil spills in polarimetric Synthetic Aperture Radar (SAR) data within the common horizontal (H) and vertical (V) polarization basis. The use of first, second, and third order sample log-cumulants has shown potential for evaluating the texture and the statistical distributions, as well as ... -
A Segmentation based CFAR detection algorithm using truncated statistics
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-01-18)Target detection in nonhomogeneous sea clutter environments is a complex and challenging task due to the capture effect from interfering outliers and the clutter edge effect from background intensity transitions. For synthetic aperture radar (SAR) measurements, those issues are commonly caused by multiple targets and meteorological and oceanographic phenomena, respectively. This paper proposes a ... -
A Multisensor Comparison of Experimental Oil Spills in Polarimetric SAR for High Wind Conditions
(Peer reviewed; Journal article; Tidsskriftsartikkel, 2016-06-23)In this paper, we present the experimental setup and data collection during the Norwegian Radar oil Spill Experiment 2015, followed by a comparison of a subset of the multisensory synthetic aperture radar (SAR) imagery collected during the experiment. Multipolarization SAR data acquired by Radarsat-2, TerraSAR-X, and the uninhabited aerial vehicle synthetic aperture radar (UAVSAR) less than 6 min ... -
Characterization and discrimination of evolving mineral and plant oil slicks based on L-band synthetic aperture radar (SAR)
(Peer reviewed; Journal article; Tidsskriftsartikkel, 2016-10-18)Evolution of the damping ratio for Bragg wavenumbers in the range 32-43 rad/m is evaluated for oil slicks of different composition released in the open ocean and allowed to develop naturally. The study uses quad-polarimetric L-band airborne synthetic aperture radar data acquired over three mineral oil emulsion releases of different, known oil-to-water ratio, and a near-coincident release of 2-ethylhexyl ... -
Level crossings, excess times, and transient plasma-wall interactions in fusion plasmas
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-04-19)Based on a stochastic model for intermittent fluctuations in the boundary region of magnetically confined plasmas, an expression for the level crossing rate is derived from the joint distribution of the process and its derivative. From this the average time spent by the process above a certain threshold level is obtained. This provides novel predictions of plasma–wall interactions due to transient ... -
Dynamics of the Terra Nova Bay Polynya: The potential of multi-sensor satellite observations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-10-10)Research on processes leading to formation, maintenance, and disappearance of polynyas in the Polar Regions benefits significantly from the use of different types of remote sensing data. The Sentinels of the European Space Agency (ESA), together with other satellite missions, provide a variety of data from different parts of the electromagnetic spectrum, at different spatial scales, and with ... -
On the improvement and acceleration of eigenvalue decomposition in spectral methods using GPUs
(Master thesis; Mastergradsoppgave, 2016-12-08)The key objectives in this thesis are; the study of GPU-accelerated eigenvalue decomposition in an effort to uncover both benefits and pitfalls, and then to investigate and facilitate a future GPU implementation of the symmetric QR algorithm with permutations. With the current trend of having ever larger datasets both in terms of features and observations, we propose that GPU computation can help ... -
Scrape-off layer turbulence in TCV: Evidence in support of stochastic modelling.
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-01-28)Intermittent fluctuations in the TCV scrape-off layer have been investigated by analysing long Langmuir probe data time series under stationary conditions, allowing calculation of fluctuation statistics with high accuracy. The ion saturation current signal is dominated by the frequent occurrence of large-amplitude bursts attributed to filament structures moving through the scrape-off layer. The ...
