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norskInstitutt for fysikk og teknologi: Nye registreringer
Viser treff 1281-1300 av 1428
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Nordlys i verdensrommet
(Journal article; Tidsskriftartikkel, 1980)Vi vil ikke her gå inn i nordlyset som vi kjenner det fra jorden, men kort omtale andre steder i verdensrommet hvor vi har observert nordlyslignende fenomen eller hvor vi kan vente å finne beslektede fenomen. -
Capillary suction model as pipes of different sizes: flow conditions and comparison with experiments
(Conference object; Konferansebidrag, 2012)ABSTRACT Absorption of water in concrete is often described by the simple linear water uptake vs. square-root-of-time law. However, a deviation from this behaviour is frequently seen depending on factors such as initial water content, water/binder ratio and specimen thickness. The deviation increases with thickness (typically from 25 to 100 mm) and is seen even for very dry specimens with ... -
Radiometric temperature reading of a hot ellipsoidal object inside the oral cavity by a shielded microwave antenna put flush to the cheek
(Journal article; Tidsskriftartikkel; Peer reviewed, 2012)A new scheme for detection of vesicoureteral reflux (VUR) in children has recently been proposed in the literature. The idea is to warm bladder urine via microwave exposure to at least fever temperatures and observe potential urine reflux from the bladder back to the kidney(s) by medical radiometry. As a preliminary step toward realization of this detection device, we present non-invasive temperature ... -
On the wake structure in streaming complex plasma
(Journal article; Tidsskriftartikkel; Peer reviewed, 2012)The theoretical description of complex (dusty) plasmas requires multiscale concepts that adequately incorporate the correlated interplay of streaming electrons and ions, neutrals and dust grains. Knowing the effective dust–dust interaction, the multiscale problem can be effectively reduced to a one-component plasma model of the dust subsystem. The goal of this paper is a systematic evaluation of the ... -
Secondary charging effects due to icy dust particle impacts on rocket payloads
(Journal article; Tidsskriftartikkel; Peer reviewed, 2012)We report measurements of dust currents obtained with a small probe and a larger probe during the flight of the ECOMA-4 rocket through the summer polar mesosphere. The payload included two small dust probes behind a larger dust probe located centrally at the front. For certain phases of the payload rotation, the current registered by one of the small dust probes was up to 2 times the current measured ... -
A Scatter-Based Prototype Framework and Multi-Class Extension of Support Vector Machines
(Journal article; Tidsskriftartikkel; Peer reviewed, 2012)We provide a novel interpretation of the dual of support vector machines (SVMs) in terms of scatter with respect to class prototypes and their mean. As a key contribution, we extend this framework to multiple classes, providing a new joint Scatter SVM algorithm, at the level of its binary counterpart in the number of optimization variables. This enables us to implement computationally efficient ... -
Blob Sizes and Velocities in the Alcator C-Mod Scrape-Off Layer
(Conference object; Konferansebidrag, 2012)A new blob-tracking algorithm for the GPI diagnostic installed in the outboard-midplane of Alcator C-Mod is developed. I t tracks large-amplitude fluctuations propagating through the scrape-off layer and calculates blob sizes and velocities. We compare the results of this method to a blob velocity scaling from a simple blob-model for sheath-connected blobs. We further present initial results from a ... -
Large amplitude blob propagation in the SOL of Alcator C-Mod and comparison to theoretical model
(Conference object; Konferansebidrag, 2012) -
Suppression of fingering instabilities in superconductors by magnetic braking
(Master thesis; Mastergradsoppgave, 2012-11)Superconductors are materials that can transport electric current without resistance and loss of energy at low temperature. This thesis is a theoretical investigation problem about the thermomagnetic instability in superconductor and its suppression by deposing a metallic layer. -
Drift wave turbulence and zonal flows
(Master thesis; Mastergradsoppgave, 2012-11-15)Anomalously large radial transport levels in fusion devices is commonly believed to be the cause of small-scale edge localized electrostatic drift wave turbulence. We review the basic drift wave instability mechanism and show how poloidally elongated structures can self-consistently emerge from the small-scale turbulent motions through envelope modulation governed by the cubic nonlinear ... -
Organization of the magnetosphere during substorms
(Journal article; Tidsskriftartikkel; Peer reviewed, 2012)The change in degree of organization of the magnetosphere during substorms is investigated by analyzing various geomagnetic indices, as well as interplanetary magnetic field z-component and solar wind velocity x-component. We conclude that the magnetosphere self-organizes globally during substorms, but neither the magnetosphere nor the solar wind become more predictable in the course of a substorm. ... -
Low-dimensionality and predictability of solar wind and global magnetosphere during magnetic storms
(Journal article; Tidsskriftartikkel; Peer reviewed, 2011)The storm index SYM-H, the solar wind velocity v, and interplanetary magnetic field Bz show no signatures of low-dimensional dynamics in quiet periods, but tests for determinism in the time series indicate that SYM-H exhibits a significant low-dimensional component during storm time, suggesting that self-organization takes place during magnetic storms. Even though our analysis yields no discernible ... -
Spectral analysis of radar coherent echoes and its relation to turbulence
(Master thesis; Mastergradsoppgave, 2012-11)The measurements of polar mesosphere summer echoes has been performed since a long time by the ground based techniques with EISCAT VHF and UHF radar system and recently with MORRO. Based on these observation, my thesis is focussed on the data obtained from manda program to get data from EISCAT 3D demonstrator antenna array in Kiruna that receives from EISCAT VHF transmitter here from Tromso in the ... -
Studies of plasma potential with emissive probes in the low temperature plasma experiment NJORD
(Master thesis; Mastergradsoppgave, 2012-11-02)In this thesis, the concept of an emissive probe has been used to obtain the plasma potential in the low temperature plasma experiment NJORD. An emissive probe is a probe concept in which a wire is heated strong enough to emit a Richardson current. The probe is then swept through several voltage biases and thus, an I-V trace obtained. With the current from the emission and the collected current, ... -
Mean shift spectral clustering using kernel entropy component analysis
(Master thesis; Mastergradsoppgave, 2012-06-01)Clustering is an unsupervised pattern recognition technique for finding natural groups in data, whether it is a grouping of web pages found by a search engine or segmenting satellite images into different types of ground cover. There exists a variety of different ways to perform clustering ranging from heuristics rules designed for a specific dataset to general procedures which can be applied to all ... -
Multi-sensor data fusion and feature extraction for forest applications
(Mastergradsoppgave; Master thesis, 2012-05-15)The purpose of this study was to extract, evaluate and select different multi-frequency polarimetric SAR and multi-spectral optical features to demonstrate the benefit of multi-sensor data fusion for forest applications. Multi-frequency fully Polarimetric SAR data at P-, L- and C-band and multi-spectral Landsat TM data acquired over the Nezer forest in France were used for demonstration. The scene ... -
Information theoretic learning with K nearest neighbors : a new clustering algorithm
(Master thesis; Mastergradsoppgave, 2012-06-01)The machine learning field based on information theory has received a lot of attention in recent years. Through kernel estimation of the probability density functions, methods developed with information theoretic measures are able to use all the statistical information available in the data, not just a finite number of moments. However, by using kernel estimation, the methods are dependent on choosing ... -
Ultrasonic imaging of pitting using multilayer synthetic aperture focusing
(Journal article; Tidsskriftartikkel; Peer reviewed, 2011)Synthetic aperture focusing is known to increase both the lateral resolution and signal-to-noise level of pulse-echo ultrasonic images. In this paper, the use of synthetic aperture imaging for detection and sizing of pitting in a plate is considered. It is assumed that a water layer is present between the transducer and the plate, and that the pitting is on the back side of the plate, seen from the ... -
Influence of Meteoric Aerosol particles on the Charge Balance in the Upper Mesosphere During ECOMA 2010
(Master thesis; Mastergradsoppgave, 2011-12-15)This work is focused on the three sounding rocket launches during the ECOMA Geminids campaign in December 2010: One before the Geminids meteor shower, one at its peak and one some days after the peak. In this work, the main emphasis is on analyzing the results from electron and ion probes on the rockets, obtaining electron and ion density profiles, and comparing them with the measurements of meteoric ... -
Semi-supervised Classification using Kernel Entropy Component Analysis and the LASSO.
(Master thesis; Mastergradsoppgave, 2011-12-15)In this thesis we present a new semi-supervised classification technique based on the Kernel Entropy Component Analysis (KECA) transformation and the least absolute shrinkage selection operator (LASSO). The latter is a constrained version of the least squares classifier. Traditional supervised classification techniques only use a limited set of labeled data to train the classifier, thus leaving ...
