Artikler, rapporter og annet (fysikk og teknologi)

A K-Wishart Markov random field model for clustering of polarimetric SAR imagery

Moser, Gabriele — Fri, 31 Dec 2010 23:00:00 GMT

Moser, Gabriele; Akbari, Vahid; Eltoft, Torbjørn; Doulgeris, Anthony Paul; Anfinsen, Stian Normann; Sebastian, Serpico

On the measurement of subsonic flow in a capacitively coupled helicon plasma source

Fredriksen, Åshild — Thu, 31 Dec 2009 23:00:00 GMT

Fredriksen, Åshild; Mishra, Lekha Nath; Gulbrandsen, Njål; Miloch, Wojciech Jacek
Plasma parameters and the subsonic flow from a capacitively coupled, cylindrical plasma source of the Njord helicon device are investigated by means of a Mach probe and a retarding field energy analyzer (RFEA). 13.56 MHz and 600 W RF power is inserted into the argon working gas under low-pressure conditions and moderate magnetic field. By means of a downstream field coil, the magnetic field is shaped from a purely expanding field to a configuration with more parallel field lines. It is shown that the downstream plasma density along the outer rim of the source increases significantly and there is a sudden increase by nearly 20 V in the plasma potential already after a moderate increase in the downstream magnetic field. The investigation of the flow indicates that current ratios derived from the Mach probe result in an apparent flow in the direction towards the source, while the current bratios derived from the RFEA indicate a flow in the direction away from the source. PIC simulations demonstrate that the acceptance angle of the probes, being nearly 180o for the Mach probe, and about 45o for the RFEA, can critically affect the current ratios and hence the subsonic flow measured by the probes in the weakly magnetized plasma in our device. The first section in your paper

Particle precipitation during NEIAL events : simultaneous ground based nighttime observations at Svalbard

Lunde, June — Wed, 31 Dec 2008 23:00:00 GMT

Lunde, June; Løvhaug, Unni Pia; Gustavsson, Björn Johan

On the secondary charging effects and structure of mesospheric dust particles impacting on rocket probes

Havnes, Ove — Sun, 31 Dec 2006 23:00:00 GMT

Havnes, Ove; Næsheim, Lars Irgens

Remote Oxygen Sensing by Ionospheric Excitation (ROSIE)

Kalogerakis, K. S. — Wed, 31 Dec 2008 23:00:00 GMT

Kalogerakis, K. S.; Gustavsson, Björn Johan; Slanger, T. G.; Rietveld, Michael T; Kendall, E. A.; Pedersen, T. R.; Kosch, M. J.

First estimates of volume distribution of HF-pump enhanced emissions at 6300 and 5577 Å : a comparison between observations and theory

Kosch, Mike — Mon, 31 Dec 2007 23:00:00 GMT

Kosch, Mike; Gustavsson, Björn Johan; Wong, Alfred; Pedersen, Todd; Heinselman, Craig; Mutiso, Charles; Bristow, Bill; Hughes, John; Wang, Weiyuan
We present bi-static observations of radio-wave induced optical emissions at 6300 and 5577 Å from a night-time radio-induced optical emission ionospheric pumping experiment at the HIPAS (Fairbanks) facility in Alaska. The optical observations were made at HIPAS and from HAARP located 285 km south-east. From these observations the altitude distribution of the emissions is estimated with tomography-like methods. These estimates are compared with theoretical models. Other diagnostics used to support the theoretical calculations include the new Poker Flat AMISR UHF radar near HIPAS. We find that the altitude distribution of the emissions agree with electron transport modeling with a source of accelerated electrons located 20 km below the upper-hybrid altitude.

A study of fine structure of diffuse aurora with ALIS-FAST measurements

Gustavsson, Björn Johan — Mon, 31 Dec 2007 23:00:00 GMT

Gustavsson, Björn Johan; Sergienko, T; Sandahl, Ingrid; Andersson, Laila; Brändström, B. U. E.; Steen, Å
We present results of an investigation of the fine structure of the night sector diffuse auroral zone, observed simultaneously with optical instruments (ALIS) from the ground and the FAST electron spectrometer from space 16 February 1997. Both the optical and particle data show that the diffuse auroral zone consisted of two regions. The equatorward part of the diffuse aurora was occupied by a pattern of regular, parallel auroral stripes. The auroral stripes were significantly brighter than the background luminosity, had widths of approximately 5 km and moved southward with a velocity of about 100 m/s. The second region, located between the region with auroral stripes and the discrete auroral arcs to the north, was filled with weak and almost homogeneous luminosity, against which short-lived auroral rays and small patches appeared chaotically. From analysis of the electron differential fluxes corresponding to the different regions of the diffuse aurora and based on existing theories of the scattering process we conclude the following: Strong pitch angle diffusion by electron cyclotron harmonic waves (ECH) of plasma sheet electrons in the energy range from a few hundred eV to 3–4 keV was responsible for the electron precipitation, that produced the background luminosity within the whole diffuse zone. The fine structure, represented by the auroral stripes, was created by precipitation of electrons above 3–4 keV as a result of pitch angle diffusion into the loss cone by whistler mode waves. A so called "internal gravity wave" (Safargaleev and Maltsev, 1986) may explain the formation of the regular spatial pattern formed by the auroral stripes in the equatorward part of the diffuse auroral zone.

F-region electron heating by X-mode radiowaves in underdense conditions

Gustavsson, Björn Johan — Wed, 31 Dec 2008 23:00:00 GMT

Gustavsson, Björn Johan; Löfås, H.; Ivchenko, N.; Rietveld, Michael T; Leyser, T. B.

A stochastic theory for temporal fluctuations in self-organized critical systems

Rypdal, Martin — Mon, 31 Dec 2007 23:00:00 GMT

Rypdal, Martin; Rypdal, Kristoffer

Spatial scaling of optical fluctuations during substorm-time aurora

Kozelov, Boris V — Sun, 31 Dec 2006 23:00:00 GMT

Kozelov, Boris V; Rypdal, Kristoffer