Artikler, rapporter og annet (fysikk og teknologi): Nye registreringer
Viser treff 581-600 av 947
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Characterization of color cross-talk of CCD detectors and its influence in multispectral quantitative phase imaging
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-02-08)Multi-spectral quantitative phase imaging (QPI) is an emerging imaging modality for wavelength dependent studies of several biological and industrial specimens. Simultaneous multi-spectral QPI is generally performed with color CCD cameras. Here, we present a new approach for accurately measuring the color crosstalk of 2D area detectors, without needing prior information about camera specifications. ... -
Super-condenser enables labelfree nanoscopy
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-08-22)Labelfree nanoscopy encompasses optical imaging with resolution in the 100 nm range using visible wavelengths. Here, we present a labelfree nanoscopy method that combines coherent imaging techniques with waveguide microscopy to realize a <i>super-condenser</i> featuring maximally inclined coherent darkfield illumination with artificially stretched wave vectors due to large refractive indices of the ... -
Maximizing Interpretability and Cost-Effectiveness of Surgical Site Infection (SSI) Predictive Models Using Feature-Specific Regularized Logistic Regression on Preoperative Temporal Data
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-02-19)This study describes a novel approach to solve the surgical site infection (SSI) classification problem. Feature engineering has traditionally been one of the most important steps in solving complex classification problems, especially in cases with temporal data. The described novel approach is based on abstraction of temporal data recorded in three temporal windows. Maximum likelihood L1-norm ... -
A red tide in the pack ice of the Arctic Ocean
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-02)In the Arctic Ocean ice algae constitute a key ecosystem component and the ice algal spring bloom a critical event in the annual production cycle. The bulk of ice algal biomass is usually found in the bottom few cm of the sea ice and dominated by pennate diatoms attached to the ice matrix. Here we report a red tide of the phototrophic ciliate <i>Mesodinium rubrum</i> located at the ice-water interface ... -
Dust trajectory simulations around Sun, Vega, and Fomalhaut
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-06-20)<p><i>Context - </i>Vega and Fomalhaut display a thermal emission brightness that can possibly arise from hot dust near the stars, an inner extension of their planetary debris disks. There was brought up an idea that nm-sized dust particles are kept in the vicinity of the stars by electromagnetic forces. This resembles the trapping that model calculations show in the corotating magnetic field in the ... -
Detection of meteoroid hypervelocity impacts on the Cluster spacecraft: First results
(Journal article; Peer reviewed, 2017-06-29)We present the first study of dust impact events on one of the Earth‐orbiting Cluster satellites. The events were identified in the measurements of the wide band data (WBD) instrument on board the satellite operating in monopole configuration. Since 2009 the instrument is operating in this configuration due to the loss of three electric probes and is therefore measuring the potential between the ... -
Single-input and multiple-output surface acoustic wave sensing for damage quantification in piezoelectric sensors
(Journal article; Peer reviewed, 2018-06-22)The main aim of the paper is damage detection at the microscale in the anisotropic piezoelectric sensors using surface acoustic waves (SAWs). A novel technique based on the single input and multiple output of Rayleigh waves is proposed to detect the microscale cracks/flaws in the sensor. A convex-shaped interdigital transducer is fabricated for excitation of divergent SAWs in the sensor. An angularly ... -
ICEBEAR: An All‐Digital Bistatic Coded Continuous Wave Radar for Studies of the E Region of the Ionosphere
(Journal article; Peer reviewed, 2019-04-15)The Ionospheric Continuous-wave E region Bistatic Experimental Auroral Radar (ICEBEAR) is a coherent scatter ionospheric radar. It operates at a frequency of 49.5 MHz, which is ideal for observing E region coherent echoes. The radar is located in Saskatchewan, Canada, and is operated by the University of Saskatchewan. The ICEBEAR system uses a continuous-wave (CW) signal and requires isolation between ... -
Improved LLM Methods Using Linear Regression
(Journal article; Peer reviewed, 2017-12-04)This paper is focused on investigations of the improved correction of the effect of variation in incidence angle on ScanSAR data. Conventional correction methods (such as LLM, locally linear mapping) typically assume that each target class has a similarity distribution in the middle of the image. The objectives of this study are to extend the correction algorithm to full swath width without any ... -
Speeding Up Non-Gaussian POLSAR Image Analysis
(Journal article; Peer reviewed, 2017-12-04)Non-Gaussian statistical models fit SAR data better than Gaussian-based statistics, in most cases, but are complicated and time-consuming to use for unsupervised image segmentation via probabilistic clustering. The more advanced the model, the more complicated and slow the clustering. The U-distribution has been demonstrated to be one of the most flexible models, capturing the Gaussian/Wishart, the ... -
Evidence of L-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith
(Journal article; Peer reviewed, 2018-02-21)The response of ionospheric plasma to pumping by powerful HF (high frequency) electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association) Heating facility in magnetic zenith. The ... -
First Simultaneous Rocket and Radar Detections of Rare Low Summer Mesospheric Clouds
(Journal article; Peer reviewed, 2018-06-10)On 30 June 2016 a layer of dust, possibly meteoric smoke particles (MSPs), was observed with a rocket borne probe at 69.29°N, 16.02°E and altitudes of ~74 km where patchy thin cloud layers, detected with the Middle Atmosphere Alomar Radar System, were present. The rocket traversed a layer with a net positive dust charge density of ~107 unit charges per cubic meters and a number density of neutral ... -
Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum
(Journal article; Peer reviewed; Tidsskriftsartikkel, 2016-12-26)Faraday rotation (FR) of transcoronal radio transmissions from spacecraft near superior conjunction enables study of the temporal variations in coronal plasma density, velocity, and magnetic field. The MESSENGER spacecraft 8.4 GHz radio, transmitting through the corona with closest line-of-sight approach 1.63–1.89 solar radii and near-equatorial heliolatitudes, was recorded soon after the deep ... -
First results from the Njord device for space related plasma experiments
(Conference object; Konferansebidrag, 2007-08-05)The Njord device at Aurolab, University of Tromsø, has been constructed to carry out experiments on instabilities and heating in plasma flows and beams, with relevance to near-Earth space plasmas. For plasma production, Njord combines a 13.56 MHz RF source with a Double Plasma chamber equipped with filaments along the walls. The source is equipped dwith two coils operated at 0-6A, providing magnetic ... -
Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-01-31)Fluctuations in plasma electron density may play a role in solar coronal energy transport and the dissipation of wave energy. Transcoronal spacecraft radio sounding observations reveal frequency fluctuations (FFs) that encode the electron number density disturbances, allowing an exploration of the coronal compressive wave and advected inhomogeneity models. Primary FF observations from MESSENGER 2009 ... -
Modeling of photovoltaic power generation and electric vehicles charging on city-scale: A review
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-19)<p>Photovoltaics (PV) and electric vehicles (EVs) are promising technologies for increasing energy efficiency and the share of renewable energy sources in power and transport systems. As regards the deployment, use and system integration of these technologies, spatio-temporal modeling of PV power production and EV charging is of importance for several purposes such as urban planning and power grid ... -
Gaussian Markov random field priors in ionospheric 3D multi-instrument tomography
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-08-22)In ionospheric tomography, the atmospheric electron density is reconstructed from different electron density related measurements, most often from ground-based measurements of satellite signals. Typically, ionospheric tomography suffers from two major complications. First, the information provided by measurements is insufficient and additional information is required to obtain a unique solution. ... -
Bistatic Observations of the Ocean Surface with HF Radar, Satellite and Airborne Receivers
(Journal article; Peer reviewed, 2017-12-25)A new concept has been developed which can view vast regions of the Earth’s surface. Ground HF transmissions are reflected by the ionosphere to illuminate the ocean over a few thousand kilometers. HF receivers detect the radio waves scattered by the sea and land surface. Using the theory of radio wave scatter from ocean surfaces, the HF data is then processed to yield the directional wave-height ... -
EISCAT 3D: the next generation international atmosphere and geospace research radar
(Journal article; Tidsskriftartikkel, 2019)EISCAT_3D is the next generation international atmosphere- and geospace research radar under development in Arctic Europe. Construction have started in September 2017 and the radar system is expected to be operational in the end of 2021. The EISCAT_3D facility will be distributed across three sites in Northern Scandinavia - in Skibotn, Norway, near Kiruna in Sweden, and near Karesuvanto in Finland. ... -
Next-generation Space Object Radar Tracking Simulator: SORTS++
(Journal article; Tidsskriftartikkel, 2019)We describe the software toolbox SORTS++ which is the next-generation Space Object Radar Tracking Simulator (SORTS). This toolbox is able to simulate general Space Surveillance and Tracking (SST) applications from catalogue maintenance to cold-start performance for radar systems or collections of radar systems. We have applied this toolbox to the EISCAT 3D radar system, currently under construction, ...