Institutt for fysikk og teknologi: Nye registreringer
Viser treff 1161-1180 av 1413
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Imaging Sea Ice Structure by Remote Sensing Sensors
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-06-14)This paper will investigate how new developments in remote sensing and sensor technologies can be applied to image the structure of the sea ice surface. Both segmentation of multipolarimetric synthetic aperture radar images and strategies for the analyses of polarimetric SAR data of sea ice are addressed. The analysis is based on a Radarsat 2 PolSAR scene of from the Fram Strait in September ... -
Characterization of a waveguide Mach-Zehnder interferometer using PDMS as a cover layer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015)A Mach-Zehnder interferometer made with shallow rib waveguides is studied experimentally and using simulations. The rib-height giving single-mode guidance is found as function of core thickness and polarization. Devices have been made using shallow rib waveguides (5 nm rib height) in silicon nitride. The sensitivity and the limit of detection (LOD) is studied experimentally regarding the length of ... -
Single-mode limit and bending losses for shallow Rib Si3N4 waveguides
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-01-07)The single-mode limit and bending losses for shallow rib waveguides are studied using the full vectorial film mode matching method. The maximum rib height for single-mode waveguides is found to be on the order of 10 nm for a rib width of 2 m and a wavelength of 785 nm, with the exact value depending on the core thickness and the polarization. Bending losses are calculated as a function of several ... -
Consensus Clustering Using kNN Mode Seeking
(Chapter; Bokkapittel, 2015-06-09)In this paper we present a novel clustering approach which combines two modern strategies, namely consensus clustering, and two stage clustering as represented by the mean shift spectral clustering algorithm. We introduce the recent kNN mode seeking algorithm in the consensus clustering framework, and the information theoretic kNN Cauchy Schwarz divergence as foundation for spectral clustering. In ... -
The auroral red line polarisation: modelling and measurements
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-12)In this work, we model the polarisation of the auroral red line using the electron impact theory developed by Bommier et al. (2011). This theory enables the computation of the distribution of the Degree of Linear Polarisation (DoLP) as a function of height if the flux of precipitated electrons is provided as input. An electron transport code is used to infer the stationary electron flux at each ... -
A case study on generation mechanisms of a sporadic sodium layer above Tromsø (69.6° N) during a night of high auroral activity
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-05)We have quantitatively evaluated generation mechanisms of a sporadic sodium layer (SSL) based on observational data obtained by multiple instruments at a high-latitude station: Ramfjordmoen, Tromsø, Norway (69.6° N, 19.2° E). The sodium lidar observed an SSL at 21:18 UT on 22 January 2012. The SSL was observed for 18 min, with a maximum sodium density of about 1.9 × 1010 m−3 at 93 km with a 1.1 km ... -
Auroral ion acoustic wave enhancement observed with a radar interferometer system
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-07-20)Measurements of naturally enhanced ion acoustic line (NEIAL) echoes obtained with a five-antenna interferometric imaging radar system are presented. The observations were conducted with the European Incoherent SCATter (EISCAT) radar on Svalbard and the EISCAT Aperture Synthesis Imaging receivers (EASI) installed at the radar site. Four baselines of the interferometer are used in the analysis. Based ... -
A comparison of overshoot modelling with observations of polar mesospheric summer echoes at radar frequencies of 56 and 224 MHz
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015)We have compared radar observations of polar mesospheric summer echoes (PMSEs) modulated by artificial electron heating, at frequencies of 224 MHz (EISCAT VHF) and 56 MHz (MORRO). We have concentrated on 1 day of observation, lasting ~ 3.8 h. The MORRO radar, with its much wider beam, observes one or more PMSE layers all the time while the VHF radar observes PMSEs in 69% of the time. Statistically ... -
Magnetic field-aligned plasma currents in gravitational fields
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-03-03)Analytical models are presented for currents along vertical magnetic field lines due to slow bulk electron motion in plasmas subject to a gravitational force. It is demonstrated that a general feature of this problem is a singularity in the plasma pressure force that develops at some finite altitude when a plasma that is initially in static equilibrium is set into slow motion. Classical fluid models ... -
Using Silver Nano-Particle Ink in Electrode Fabrication of High Frequency Copolymer Ultrasonic Transducers: Modeling and Experimental Investigation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-04-20)High frequency polymer-based ultrasonic transducers are produced with electrodes thicknesses typical for printed electrodes obtained from silver (Ag) nano-particle inks. An analytical three-port network is used to study the acoustic effects imposed by a thick electrode in a typical layered transducer configuration. Results from the network model are compared to experimental findings for the implemented ... -
The First Magnetotelluric Image of the Lithospheric-Scale Geological Architecture in Central Svalbard, Arctic Norway
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-12-17)Magnetotelluric data, collected from 30 stations on Spitsbergen as part of a reconnaissance geothermal resource assessment along a profile with 0.53-km spacing in 0.0031000-s period range, were used to develop a lithospheric-scale two-dimensional (2D) resistivity model, heretofore unavailable for the region. Inverting the determinant of the impedance tensor in 2D, we found the smoothest model ... -
On the Relationship between PMSE Strength and Particle Precipitation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-06)We have studied the relationship between particle precipitation and PMSE strength on days where we observe PMSE layers both with the EISCAT VHF and UHF radars. The UHF observations of the ionization and its variation, above the PMSE layer, is used as a measure of precipitation. Variations of the precipitation is compared with variations of the PMSE strengths observed with both radars. Although ... -
Preliminary Assessment of Remote Wind Sites
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08)Wind energy is becoming a reliable and affordable source of clean energy and is rapidly expanding to remote places around the world. A crucial input for wind farming prospect is the assessment of potential wind sites. Sites, especially remotely located, often do not have a wind resource map and thus lack credible historical records of wind resources. Measurement campaigns to map these sites are ... -
CFD-DEM and Experimental Study of Bubbling in a Fluidized Bed
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-12)In this study, phenomenon of bubbling is investigated using CFD-DEM and experiments. A CFD-DEM simulation is setup to model the fluidized beds of different sizes. Geldart D particles of 1.2 mm diameter and 1000 Kg/m3 density are modelled. Study revealed different types of fluidization regimes as stated in the literature. An experimental setup is built to obtain the results for the comparison. ... -
Short-Time Ice Drift and Deformation Measurements Using Multi-Mission Synethetic Aperture Radar
(Journal article; Tidsskriftartikkel, 2015-06)Norway is in a good position regarding frequent access to synthetic aperture radar data. A Norwegian– Canadian agreement provides large quotas of RADARSAT-2 images used operationally by e.g. the Norwegian Ice Service. More recently, Norway’s participation in the Copernicus program also allows rapid access to SENTINEL-1A data. By combining these data sources we can get satellite time series ... -
Stochastic modelling of intermittent scrape-off layer plasma fluctuations
(Master thesis; Mastergradsoppgave, 2015-05-15)In the tokamak scrape-off layer, radial motion of blob-like structures is the dominant mechanism for transport of particles and heat. Fixed point probe measurements in the Tokamak à Configuration Variable scrape-off layer reveal highly intermittent fluctuations in the ion saturation current. These measurements are well described by a shot noise process with exponential pulse shapes, exponentially ... -
Statistical Unmixing of SAR Images
(Journal article; Tidsskriftartikkel, 2016-02-03)A method is presented which uses logarithmic statistics to detect and characterise class mixtures and targets in background clutter in synthetic aperture radar (SAR) images. Mixtures of ground cover types show up as extreme radar texture in statistical analysis of SAR images. Instead of modelling this as a spatially nonstationary radar cross section, this paper demonstrates how a mixture model ... -
Linear scaling Coulomb interaction in the multiwavelet basis, a parallel implementation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-08-27)We present a parallel and linear scaling implementation of the calculation of the electrostatic potential arising from an arbitrary charge distribution. Our approach is making use of the multi-resolution basis of multiwavelets. The potential is obtained as the direct solution of the Poisson equation in its Green’s function integral form. In the multiwavelet basis, the formally non local ... -
Mesospheric temperatures and sodium properties measured with the ALOMAR Na lidar compared with WACCM
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-01-16)We present a comparison of the temperature and sodium layer properties observed by the ALOMAR Na lidar (69.3°N, 16.0°E) and simulated by the Whole Atmosphere Community Climate Model with specified dynamics and implemented sodium chemistry (WACCM-Na). To constrain the meteorological fields below 60 km, we use MERRA and GEOS-5. For the years 2008 to 2012, we analyse daily averages of temperature ... -
Shallow fluid seepage systems in the Hammerfest Basin and adjacent Fault complex
(Master thesis; Mastergradsoppgave, 2015-08-12)This study was carried out using three high resolution 3D P-cable seismic datasets to explore shallow gas distribution and possible fluid migration pathways in the Snøhvit field and Ringvassøy-Loppa Fault Complex. The Snøhvit field situated in the center of the Hammerfest Basin is oil and gas field discovered in 1994. Ringvassøy-Loppa Fault complex marks the border between the Hammerfest and Tromsø ...