Institutt for fysikk og teknologi: Recent submissions
Now showing items 421-440 of 1402
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Machine Learning Detection of Dust Impact Signals Observed by The Solar Orbiter
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-08-11)This article present results from automatic detection of dust impact signals observed by the Solar Orbiter – Radio and Plasma Waves instrument.<p> <p>A sharp and characteristic electric field signal is observed by the Radio and Plasma Waves instrument when a dust particle impact the spacecraft at high velocity. In this way, ∼5–20 dust impacts are daily detected as the Solar Orbiter travels through ... -
Deep microlocal reconstruction for limited-angle tomography
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-01-04)We present a deep-learning-based algorithm to jointly solve a reconstruction problem and a wavefront set extraction problem in tomographic imaging. The algorithm is based on a recently developed digital wavefront set extractor as well as the well-known microlocal canonical relation for the Radon transform. We use the wavefront set information about x-ray data to improve the reconstruction ... -
Formation of ice particles through nucleation in the mesosphere
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-04-28)Observations of polar mesospheric clouds have revealed the presence of solid ice particles in the upper mesosphere at high latitudes; however, their formation mechanism remains uncertain. In this study, we investigated the formation process of ice particles through nucleation from small amounts of water vapor at low temperatures. Previous studies that used classical nucleation theory have shown ... -
Report From Surveys To Assess Harp And Hooded Seal Pup Production In The Greenland Sea Pack-Ice In 2022
(Research report; Forskningsrapport, 2022-06-07)Cruise no.: 2022703 : The 2022 survey of harp and hooded seal pup production in the Greenland Sea was carried out to obtain updated estimates to be used to assess current status of these two seal stocks. Since a similar survey in 2018 indicated a 40% reduction in harp seal pup production since the 2012 survey, and the continued lack of increase in pup production of the severely depleted hooded ... -
Thermodynamic and dynamic contributions to seasonal Arctic sea ice thickness distributions from airborne observations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-04-18)Sea ice thickness is a key parameter in the polar climate and ecosystem. Thermodynamic and dynamic processes alter the sea ice thickness.The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition provided a unique opportunity to study seasonal sea ice thickness changes of the same sea ice. We analyzed 11 large-scale (*50 km) airborne electromagnetic sea thickness ... -
Validation of Multistatic Meteor Radar Analysis Using Modeled Mesospheric Dynamics: An Assessment of the Reliability of Gradients and Vertical Velocities
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-28)A virtual meteor radar system based on the upper-atmosphere extension of the high-resolution ICOsahedral Non-hydrostatic general circulation model is constructed to validate multistatic specular meteor radar (SMR) analyses. The virtual radar system examines the validity of mean winds and gradients estimation techniques used in multistatic SMRs. The study is motivated by unexpected mean values and ... -
2022 Tonga Volcanic Eruption Induced Global Propagation of Ionospheric Disturbances via Lamb Waves
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-23)The Tonga volcano eruption at 04:14:45 UT on 2022-01-15 released enormous amounts of energy into the atmosphere, triggering very significant geophysical variations not only in the immediate proximity of the epicenter but also globally across the whole atmosphere. This study provides a global picture of ionospheric disturbances over an extended period for at least 4 days. We find traveling ionospheric ... -
ICEBEAR-3D: A Low Elevation Imaging Radar Using a Non-Uniform Coplanar Receiver Array for E Region Observations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-19)The Ionospheric Continuous-wave E region Bistatic Experimental Auroral Radar (ICEBEAR) has been reconfigured using a phase error minimization and stochastic antenna location perturbation technique. The resulting 45-baseline sparse non-uniform coplanar T-shaped array, ICEBEAR-3D, is used for aperture synthesis radar imaging of low elevation targets. The reconfigured receiver antenna array now has ... -
Inference Guided Few-Shot Segmentation
(Master thesis; Mastergradsoppgave, 2022-06-22)Few-shot segmentation has in recent years gotten a lot of attention. The reason is its ability to segment images from classes based on only a handful of labeled support images. This opens up many possibilities when the need for a big dataset is removed. To do this a few-shot segmentation network need to extract as much quality information from each support image as possible. In this thesis we ... -
Rossby Wave Changes During the Recent Decades in Mid-Latitude Continents in the Northern Hemisphere
(Master thesis; Mastergradsoppgave, 2022-06-22)Increasing frequency and severity of extreme weather events throughout the recent years is a highly concerning topic. Extreme and unusual weather conditions, such as heat waves, floods and cold spells are causing a major concern for humanity. Agricultural changes, damages in infrastructure and the loss of human lives are some of the extreme weather event consequences, with the most drastic consequences ... -
Finite element simulation of transmission and reflection of acoustic waves in the ultrasonic transducer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-30)In scanning acoustic microscopy (SAM), the image quality depends on several factors such as noise level, resolution, and interaction of the waves with sample boundaries. The theoretical equations for the reflection coefficient and transmission coefficient are suitable for plane boundaries but fail for curved/rough boundaries. We presented a finite element method-based modeling for the loss ... -
Plasma-neutral gas interactions in various space environments: Assessment beyond simplified approximations as a Voyage 2050 theme
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-26)In the White Paper, submitted in response to the European Space Agency (ESA) Voyage 2050 Call, we present the importance of advancing our knowledge of plasma-neutral gas interactions, and of deepening our understanding of the partially ionized environments that are ubiquitous in the upper atmospheres of planets and moons, and elsewhere in space. In future space missions, the above task ... -
Network Analysis and Boosting the Distribution to Local Consumers at Northern Senja, Norway with Potential Renewable Generation using Power Flow Control
(Master thesis; Mastergradsoppgave, 2022-06-08)Renewable generation and power flow control are increasing its importance for power systems. The promising development in the technology increases the efficiency for transferring energy. With increasing consumption, remote locations benefit from close laying power production due to reduced transfer losses. In these recent years, energy storage system and local renewable energy production injected ... -
Solar Photovoltaic Potential on Commercial Buildings in Arctic Latitudes
(Master thesis; Mastergradsoppgave, 2022-06-01)This thesis desires to study the use of solar resources in a less frequently used location, by exploring the use of a photovoltaic systems on the roof of a warehouse in Tromsø, Norway. The research is gathered using a 15 000 𝑚2 warehouse as the location, which has an annual energy consumption of 2,9 GWh. The solar resources at this location are highly dependent on season, with periods of polar ... -
Assessment of Solar Photovoltaics and Wind Energy for Increased Electrification and Grid Independent Farming
(Master thesis; Mastergradsoppgave, 2022-05-31)A solution towards increased electrification and reduced greenhouse gas emissions in the agriculture is local renewable energy production. Not only is it a sustainable and environmentally positive project, but with remarkably increasing electricity prices renewable energy projects can also be economically favorable for farmers, by reducing grid dependence and hence high electricity costs. In this ... -
DC-Approximated Power System Reliability Predictions with Graph Convolutional Neural Networks
(Master thesis; Mastergradsoppgave, 2022-05-30)The current standard operational strategy within electrical power systems is done following deterministic reliability practices. These practices are deemed to be secure under most operating situations when considering power system security, but as the deterministic practices do not consider the probability and consequences of operation, the operating situation may often become either too strict or ... -
Generating customer's credit behavior with deep generative models
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-17)Banks collect data x<sub>1</sub> in loan applications to decide whether to grant credit and accepted applications generate new data x<sub>2</sub> throughout the loan period. Hence, banks have two measurement-modalities, which provide a complete picture about customers. If we can generate x<sub>2</sub> conditioned on x<sub>1</sub> keeping the relationship between these two modalities, credit and ... -
Anomaly detection-inspired few-shot medical image segmentation through self-supervision with supervoxels
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-11)Recent work has shown that label-efficient few-shot learning through self-supervision can achieve promising medical image segmentation results. However, few-shot segmentation models typically rely on prototype representations of the semantic classes, resulting in a loss of local information that can degrade performance. This is particularly problematic for the typically large and highly heterogeneous ... -
Evaluation of crystalline structure quality of Czochralski-silicon using near-infrared tomography
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-01-22)In this work, three silicon samples are subject to tomographic scans using a 1.6μm laser. The samples were prematurely terminated due to anomalies during the Czhochralski-process. They are taken as analogues of the in situ crystal, where one sample has known aberrant structure in its lowermost 45 mm. The results of the tomographic scans show a distinct difference in transmission profile between ... -
Electron-neutral collisions effects on Langmuir probe in the lower E-region ionosphere
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-03-21)We present the first set of particle-in-cell simulations including Monte Carlo collisions between charged and neutral particles used to simulate a cylindrical Langmuir probe in the electron saturation regime with a collisional electron sheath. We use a setup focused on the E-region ionosphere; however, the results of these simulations are analyzed in a general sense using dimensionless values. We ...