Institutt for fysikk og teknologi: Recent submissions
Now showing items 241-260 of 1294
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Machine learning approach for identification and tracking of coherent structures in turbulent fluids and plasmas
(Master thesis; Mastergradsoppgave, 2022-12-15)In a fusion reactor, coherent structures of hot and dense plasma can drift radially outwards due to the conditions of the edge plasma and can cause erosion of the outer walls. This erosion can release impurities into the plasma and harm equipment at the walls. This thesis presents two methods of tracking blobs in the boundary region of fusion experiments. The first model is a simple Long Short-Term ... -
Using radar beam-parks to characterize the Kosmos-1408 fragmentation event
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-10-22)We describe the use of radar beam-park experiments to characterize the space debris resulting from a recent fragmentation event, the deliberate demolition of the defunct Kosmos-1408 satellite. We identify the Kosmos-1408 fragments and present distribution of measurement parameters as well as proxy orbit parameters. We present and apply a novel technique to estimate the size of objects by matching ... -
Manx Arrays: Perfect Non-Redundant Interferometric Geometries
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-09-09)Interferometry applications (e.g., radio astronomy) often wish to optimize the placement of the interferometric elements. One such optimal criterion is a uniform distribution of non-redundant element spacings (in both distance and position angle). While large systems, with many elements, can rely on saturating the sample space, and disregard “wasted” sampling, small arrays with only a few elements ... -
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 ... -
The future of auroral E-region plasma turbulence research
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-12-15)The heating caused by ionospheric E-region plasma turbulence has documented global implications for the energy transfer from space into the terrestrial atmosphere. Traveling atmospheric disturbances, neutral wind motion, energy deposition rates, and ionospheric conductance have all been shown to be potentially affected by turbulent plasma heating. Therefore it is proposed to enhance and expand ... -
Time-Dependent Electron Transport I: Modelling of Supra-Thermal Electron Bursts Modulated at 5–10 Hz With Implications for Flickering Aurora
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-04)A time-dependent multi-stream electron transport model, AURORA, has been developed for studies of auroral emission-rates during precipitation with large variations on sub-second time-scales. The transport-code accurately takes time-of-flight, energy degradation, scattering and production of secondary electrons into account. AURORA produces ionospheric electron-flux as a function of energy, altitude, ... -
On the origin of bonding in metals: lithium as a case study
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-09-05)The bonding in metals is analysed within the framework of the PATMOS (Perturbed AToms in MOlecules and Solids) model. The electronic binding energy per atom is written as a sum of a distortion energy of the atoms and the partitioned interaction energy comprising Coulombic, exchange and correlation terms. The adopted physical model of the infinite system, is spherical embedding of the atoms of the ... -
Functional Connectome of the Human Brain with Total Correlation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-25)Recent studies proposed the use of Total Correlation to describe functional connectivity among brain regions as a multivariate alternative to conventional pairwise measures such as correlation or mutual information. In this work, we build on this idea to infer a large-scale (whole-brain) connectivity network based on Total Correlation and show the possibility of using this kind of network as ... -
Automatic detection of the mental foramen for estimating mandibular cortical width in dental panoramic radiographs: the seventh survey of the Tromsø Study (Tromsø7) in 2015-2016
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-22)Objective To apply deep learning to a data set of dental panoramic radiographs to detect the mental foramen for automatic assessment of the mandibular cortical width.<p> <p>Methods Data from the seventh survey of the Tromsø Study (Tromsø7) were used. The data set contained 5197 randomly chosen dental panoramic radiographs. Four pretrained object detectors were tested. We randomly chose 80% of the ... -
Multiple Damage Detection in PZT Sensor Using Dual Point Contact Method
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-25)Lead Zirconate Titanate (PZT) is used to make ultrasound transducers, sensors, and actuators due to its large piezoelectric coefficient. Several micro-defects develop in the PZT sensor due to delamination, corrosion, huge temperature fluctuation, etc., causing a decline in its performance. It is thus necessary to identify, locate, and quantify the defects. Non-Destructive Structural Health Monitoring ... -
A Comparative Study of PMETAC-Modified Mesoporous Silica and Titania Thin Films for Molecular Transport Manipulation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-09)The manipulation and understanding of molecular transport across functionalized nanopores will take us closer to mimicking biological membranes and thus to design high-performance permselective separation systems. In this work, Surface-initiated atom transfer radical polymerization (SI-ATRP) of (2-methacryloyloxy)-ethyltrimethylammonium chloride (METAC) was performed on both mesoporous silica and ... -
Supervised Classifications of Optical Water Types in Spanish Inland Waters
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-04)Remote sensing of lake water quality assumes there is no universal method or algorithm that can be applied in a general way on all inland waters, which usually have different in-water components affecting their optical properties. Depending on the place and time of year, the lake dynamics, and the particular components of the water, non-tailor-designed algorithms can lead to large errors or lags in ... -
Spatial variability of nocturnal stability regimes in an operational weather prediction model
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-15)Forecast errors in near-surface temperatures are a persistent issue for numerical weather prediction models. A prominent example is warm biases during cloud-free, snow-covered nights. Many studies attribute these biases to parametrized processes such as turbulence or radiation. Here, we focus on the contribution of physical processes to the nocturnal temperature development. We compare model timestep ... -
Traveling Ionospheric Disturbances in the Vicinity of Storm-Enhanced Density at Midlatitudes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-08-08)This study provides first storm time observations of the westward-propagating medium-scale traveling ionospheric disturbances (MSTIDs), particularly, associated with characteristic subauroral storm time features, storm-enhanced density (SED), subauroral polarization stream (SAPS), and enhanced thermospheric westward winds over the continental US. In the four recent (2017–2019) geomagnetic storm ... -
Impulse-driven oscillations of the near-Earth's magnetosphere
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-09)It is argued that a simple model based on magnetic image arguments suffices to give a convincing insight into both the basic static as well as some transient dynamic properties of the near-Earth's magnetosphere, particularly accounting for damped oscillations being excited in response to impulsive perturbations. The parameter variations of the frequency are given. Qualitative results can also be ... -
Scalable-resolution structured illumination microscopy
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-15)Structured illumination microscopy suffers from the need of sophisticated instrumentation and precise calibration. This makes structured illumination microscopes costly and skill-dependent. We present a novel approach to realize super-resolution structured illumination microscopy using an alignment non-critical illumination system and a reconstruction algorithm that does not need illumination ... -
Errors in Simple Climate Model Emulations of Past and Future Global Temperature Change
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-08-04)Climate model emulators are widely used to generate temperature projections for climate scenarios, including in the recent Intergovernmental Panel on Climate Change Sixth Assessment Report. Here we evaluate the performance of a two-layer energy balance model in emulating historical and future temperature projections from Coupled Model Intercomparison Project Phase 6 models. We find that emulation ... -
On the Exploitation of Multimodal Remote Sensing Data Combination for Mesoscale/Submesoscale Eddy Detection in the Marginal Ice Zone
(Journal article; Tidsskriftartikkel, 2022-10-17)The detection and analysis of ocean eddies via remote sensing have become a hot topic in physical oceanography during the last few decades. However, eddy identification and tracking via remote sensing can be a challenging task, since each sensor has some limitations. In order to overcome potential challenges, it is crucial to exploit the complementary information provided by different sensing systems. ... -
Negational symmetry of quantum neural networks for binary pattern classification
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-04-27)Although quantum neural networks (QNNs) have shown promising results in solving simple machine learning tasks recently, the behavior of QNNs in binary pattern classification is still underexplored. In this work, we find that QNNs have an Achilles’ heel in binary pattern classification. To illustrate this point, we provide a theoretical insight into the properties of QNNs by presenting and analyzing ... -
Reconstruction of precipitating electrons and three-dimensional structure of a pulsating auroral patch from monochromatic auroral images obtained from multiple observation points
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-07-12)In recent years, aurora observation networks using high-sensitivity cameras have been developed in the polar regions. These networks allow dimmer auroras, such as pulsating auroras (PsAs), to be observed with a high signal-to-noise ratio. We reconstructed the horizontal distribution of precipitating electrons using computed tomography with monochromatic PsA images obtained from three observation ...