Institutt for fysikk og teknologi
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Addressing Label Shift in Distributed Learning via Entropy Regularization
(Journal article; Tidsskriftartikkel; Peer reviewed, 2025-01-22)We address the challenge of minimizing "true risk" in multi-node distributed learning.\footnote{We use the term node to refer to a client, FPGA, APU, CPU, GPU, or worker.} These systems are frequently exposed to both inter-node and intra-node "label shifts", which present a critical obstacle to effectively optimizing model performance while ensuring that data remains confined to each node. To tackle ... -
Long-range correlations with finite-size effects from a superposition of uncorrelated pulses with power-law distributed durations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2025-02-26)Long-range correlations manifested as power spectral density scaling 1/<i>f<sup>β</sup></i> for frequency f and a range of exponents <i>β</i> are investigated for a superposition of uncorrelated pulses with distributed durations τ. Closed-form expressions for the frequency power spectral density are derived for a one-sided exponential pulse function and several variants of bounded and unbounded ... -
Impact of oxidized low-density lipoprotein on rat liver sinusoidal endothelial cell morphology and function.
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-10-23)Atherogenesis is associated with elevated plasma levels of oxidized low-density lipoproteins (oxLDL). In vivo, oxLDL causes liver endothelial swelling, and disrupts liver sinusoidal endothelial cell (LSECs) fenestrations. We mapped the nanoscale kinetics of these changes in vitro in isolated rat LSECs challenged with oxLDL and monitored viability with endocytosis and cytotoxicity assays. OxLDL ... -
Development of a Multi-angle Illumination Microscope for 3D Refractive Index Reconstruction
(Mastergradsoppgave; Master thesis, 2024-12-17)This thesis presents the design,implementation,and evaluation of a multi-angle illumination micro- scope tailored for 3D refractive index (ri) reconstruction using the Multi-Slice Beam Propagation (msbp) method. The system combines custom-built hardware, including precision-aligned optical components and motorized kinematic mirrors, with computational algorithms developed in Python toachievehi ... -
Numerical simulations of coherent blob-like filaments in magnetized plasmas
(Mastergradsoppgave; Master thesis, 2024-12-16)In a world more and more dependent on new and effective energy sources, the introduction of fusion power could prove invaluable. Magnetic confinement of plasma has proved to be difficult, and the curvature of the magnetic field lines in tokamaks give rise to charge polarization at the boundary of the fusion devices leading to cross-field transport. Experiments has shown that the dominating transport ... -
Introducing Glycemic Index to Blood Glucose Simulations and its effect on Food Recommendation Systems
(Mastergradsoppgave; Master thesis, 2024-12-02)The availability of In-Silco blood glucose simulators that accurately depict all aspects of Diabetes Mellitus patient’s daily life is crucial for the development of safe and effective new treatment technologies. Current state of the art simulators focus on modeling a meal’s effect on the glucose-insulin system solely based on the quantity of carbohydrates consumed. However not only the quantity of ... -
Enhancing assessment of direct and indirect exposure of settlement-transportation systems to mass movements by intergraph representation learning
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-10-14)Amidst the intensifying extreme rainfall patterns due to climate change, global early warning systems for mass movements (e.g. landslides, avalanches) need to provide not only the coarsely aggregated danger reports, but also the necessary fine details to understand its potential implications on critical infrastructures such as transportation systems. In this study, we introduce a novel ‘intergraph’ ... -
Incidence angle dependency and seasonal evolution of L and C-band SAR backscatter over landfast sea ice
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-10-02)We estimate sea-ice type specific incidence angle (IA) dependencies for dual polarized (HH/HV) L and C-band synthetic aperture radar (SAR) for the winter, melt onset and advanced melt seasons for level and deformed ice, using time-series of Advanced Land Observing Satellite-2 (ALOS-2) and Sentinel-1 imagery off the north-east coast of Greenland. The IA dependencies are used to radiometrically ... -
Improving Land Surface Temperature Estimation in Cloud Cover Scenarios Using Graph-Based Propagation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-12-03)Land surface temperature (LST) serves as an important climate variable which is relevant to a number of studies related to energy and water exchanges, vegetation growth and urban heat island effects. Although LST can be derived from satellite observations, these approaches rely on cloud‐free acquisitions. This represents a significant obstacle in regions which are prone to cloud cover. In this ... -
Computing-Model and Computing-Hardware Selection for ICT under Societal and Judicial Constraints
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-12-18)This article discusses a formalization of aspects of Cyber-Sovereignty (CyS) for information and communication technology (ICT), linking them to technological trustworthiness and deriving an associated paradigm for hard- and software design. The upcoming 6G ICT standard is considered a keystone within modern society’s increasing interconnectedness and automatization, as it provides the ... -
On the Identification of the Dayside Auroral Region Using Incoherent Scatter Radar
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-12-22)This paper presents a robust method combining electron temperatures and density to identify the winter dayside auroral region in Incoherent Scatter Radar (ISR) observations. In literature, a common proxy for identifying the dayside auroral region has been enhanced electron temperatures T<sub>e</sub> at high altitudes. However, T<sub>e</sub> is intimately related to N<sub>e</sub> and their ... -
Suspended nanophotonic waveguide for isotope-specific CO2 detection
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-12-11)The spectroscopic detection of gases and their stable isotopes holds significant value in bio-sciences and climate studies. However, achieving high precision has long been confined to bulky and costly equipment. In this work, we introduce a nanophotonic waveguide that is capable of detecting CO<sub>2</sub> gas down to 20 parts per billion, and for the first time perform accurate stable isotope ratio ... -
Recognizing Hand-Based Micro Activities Using Wrist-Worn Inertial Sensors: A Zero-Shot Learning Approach
(Chapter; Bokkapittel, 2024-10-23)Zero-shot learning (ZSL) is a machine learning paradigm that enables models to recognize and classify data from classes they have not encountered during training. This approach is particularly advantageous in recognizing activities where labeled data is limited, allowing models to identify new, unseen activities by leveraging semantic knowledge from seen activities. In this paper, we explore the ... -
Automatic Generation of Contrast Maps in Terms of van der Waals Material Properties in Bimodal AFM
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-11-26)van der Waals (vdW) forces are of interest in colloid science, biophysics, cell biology, and the field of vdW heterostructures. We present a model and method to quantify vdW material properties of samples routinely in standard bimodal atomic force microscopy (AFM) without the need to establish mechanical contact with the samples. The method preserves the high resolution of bimodal AFM but ... -
A position and wave spectra dataset of Marginal Ice Zone dynamics collected around Svalbard in 2022 and 2023
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-12-21)Sea ice is a key element of the global Earth system, with a major impact on global climate and regional weather. Unfortunately, accurate sea ice modeling is challenging due to the diversity and complexity of underlying physics happening there, and a relative lack of ground truth observations. This is especially true for the Marginal Ice Zone (MIZ), which is the area where sea ice is affected by ... -
A Practical Approach to FMCW Radar Deconvolution in the Sea Ice Domain
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-11-19)This paper presents a practical step-by-step approach to Frequency Modulated Continuous Wave (FMCW) radar nonlinearity correction (deconvolution), utilizing surface-based Ku- and Ka-band radar data collected over nilas ice within a newly-opened sea ice lead during the 2019/2020 MOSAiC expedition. Two performance metrics are introduced to evaluate deconvolution effectiveness: the spurious free ... -
Heavy Molecular and Metallic Ions in the Magnetosphere
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-11-04)Observations and present knowledge of heavy ions with mass ≥ 27 in the magnetosphere are reviewed. There are four ultimate sources of these heavy ions: the solar wind (mainly high charge-state atomic ions), the ionosphere (mainly molecular ions), the atmospheric metal layers that originate ultimately from ablation of meteoroids and possibly space debris (low charge-state metallic ions and metal-rich ... -
The Growth and Decay of Intense GNSS Amplitude and Phase Scintillation During Non‐Storm Conditions
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-11-30)A multi‐instrument study is conducted at the dayside polar ionosphere to investigate the spatio‐ temporal evolution of scintillation in Global Navigation Satellite System (GNSS) signals during non‐storm conditions. Bursts of intense amplitude and phase scintillation started to occur at ∼9 MLT and persisted for more than 1 hour implying the simultaneous existence of Fresnel and large‐scale sized ... -
Leveraging Network Science for the Exploration of Deep Learning Latent Representations
(Mastergradsoppgave; Master thesis, 2023-12-15)Deep Neural networks has pushed the boundary for what is achievable in the field of machine learning. At its core the Neural network maps data from an input space, to a highly abstract latent space. The representations of these latent mappings are critical for the neural networks ability to perform the task it is given. However critical, our knowledge on these abstract representations in the latent ... -
Impact of varying solar angles on Arctic iceberg area retrieval from Sentinel-2 near-infrared data
(Journal article; Tidsskriftartikkel; Peer reviewed, 2024-11-18)Icebergs are part of the glacial mass balance and they interact with the ocean and with sea ice. Optical satellite remote sensing is often used to retrieve the above-waterline area of icebergs. However, varying solar angles introduce an error to the iceberg area retrieval that had not been quantified. Herein, we approximate the iceberg area error for top-of-atmosphere Sentinel-2 near-infrared data ...