| 1. |
- Bouyoucef, S E, et al.
(författare)
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Poster Session 2 : Monday 4 May 2015, 08
- 2015
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Ingår i: European Heart Journal Cardiovascular Imaging. - : Oxford University Press (OUP). - 2047-2404 .- 2047-2412. ; 16 Suppl 1
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Ferreira, Mjv, et al.
(författare)
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Poster Session 3 : Tuesday 5 May 2015, 08
- 2015
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Ingår i: European Heart Journal Cardiovascular Imaging. - : Oxford University Press (OUP). - 2047-2404 .- 2047-2412. ; 16 Suppl 1
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Pellegrino, T, et al.
(författare)
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Moderated Poster Session 3 : Monday 4 May 2015, 10
- 2015
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Ingår i: European Heart Journal Cardiovascular Imaging. - : Oxford University Press (OUP). - 2047-2404 .- 2047-2412. ; 16 Suppl 1
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Tidskriftsartikel (refereegranskat)
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| 4. |
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| 5. |
- Kero, J., et al.
(författare)
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The 2009-2010 MU radar head echo observation programme for sporadic and shower meteors : radiant densities and diurnal rates
- 2012
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Ingår i: Monthly notices of the Royal Astronomical Society. - Hoboken, NJ : Wiley-Blackwell. - 0035-8711 .- 1365-2966. ; 425:1, s. 135-146
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to give an overview of the monthly meteor head echo observations (528.8?h) conducted between 2009 June and 2010 December using the Shigaraki Middle and Upper atmosphere radar in Japan (34 degrees.85 N, 136 degrees.10 E). We present diurnal detection rates and radiant density plots from 18 separate observational campaigns, each lasting for at least one diurnal cycle. Our data comprise more than 106?000 meteors. All six recognized apparent sporadic meteor sources are discernable and their average orbital distributions are presented in terms of geocentric velocity, semimajor axis, inclination and eccentricity. The north and south apex have radiant densities an order of magnitude higher than other apparent source regions. The diurnal detection rates show clear seasonal dependence. The main cause of the seasonal variation is the tilt of the Earth's axis, causing the elevation of the Earth's apex above the local horizon to change as the Earth revolves around the Sun. Yet, the meteor rate variation is not symmetric with respect to the equinoxes. When comparing the radiant density at different times of the year, and thus at different solar longitudes along the Earth's orbit, we have found that the north and south apex source regions fluctuate in strength.
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| 6. |
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| 7. |
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| 8. |
- Kero, Johan, et al.
(författare)
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A meteor head echo analysis algorithm for the lower VHF band
- 2012
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Ingår i: Annales Geophysicae. - Gottingen : Copernicus Gesellschaft mbH. - 0992-7689 .- 1432-0576. ; 30:4, s. 639-659
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Tidskriftsartikel (refereegranskat)abstract
- We have developed an automated analysis scheme for meteor head echo observations by the 46.5 MHz Middle and Upper atmosphere (MU) radar near Shigaraki, Japan (34.85A degrees N, 136.10A degrees E). The analysis procedure computes meteoroid range, velocity and deceleration as functions of time with unprecedented accuracy and precision. This is crucial for estimations of meteoroid mass and orbital parameters as well as investigations of the meteoroid-atmosphere interaction processes. In this paper we present this analysis procedure in detail. The algorithms use a combination of single-pulse-Doppler, time-of-flight and pulse-to-pulse phase correlation measurements to determine the radial velocity to within a few tens of metres per second with 3.12 ms time resolution. Equivalently, the precision improvement is at least a factor of 20 compared to previous single-pulse measurements. Such a precision reveals that the deceleration increases significantly during the intense part of a meteoroid's ablation process in the atmosphere. From each received pulse, the target range is determined to within a few tens of meters, or the order of a few hundredths of the 900 m long range gates. This is achieved by transmitting a 13-bit Barker code oversampled by a factor of two at reception and using a novel range interpolation technique. The meteoroid velocity vector is determined from the estimated radial velocity by carefully taking the location of the meteor target and the angle from its trajectory to the radar beam into account. The latter is determined from target range and bore axis offset. We have identified and solved the signal processing issue giving rise to the peculiar signature in signal to noise ratio plots reported by Galindo et al. (2011), and show how to use the range interpolation technique to differentiate the effect of signal processing from physical processes.
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| 9. |
- Kero, J., et al.
(författare)
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MU radar head echo observations of the 2011 October Draconids
- 2012
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Ingår i: Monthly notices of the Royal Astronomical Society. - Hoboken, NJ : Wiley-Blackwell. - 0035-8711 .- 1365-2966. ; 424:3, s. 1799-1806
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Tidskriftsartikel (refereegranskat)abstract
- On 2011 October 8, the Earth passed through a stream of dust ejected by the comet 21P/GiacobiniZinner during its perihelion passage of the year 1900, causing an outburst of October Draconid meteors. 13 Draconids were observed among similar to 6300 meteor head echoes with precisely determined orbits during an observational campaign ranging from October 8 05:00 ut to October 9 13:00 ut with the Shigaraki middle and upper atmosphere (MU) radar in Japan (34 degrees.85?N and 136 degrees.10?E). The meteor outburst occurred while the Draconid radiant was descending below and 2?h later rising up above the horizon. Therefore, 11 of the detections were from very low (<15 degrees) elevation. The detection altitudes of the Draconids were high compared to sporadic meteors of the same velocity and radiant elevation. The weighted mean geocentric velocity of the 13 Draconids was 20.6 +/- 0.4?km?s-1, and the weighted mean radiant located at right ascension alpha = 263 degrees.3 +/- 0 degrees.6 and declination delta = 55 degrees.8 +/- 0 degrees.2.
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| 10. |
- Oyama, Shin-ichiro, et al.
(författare)
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Auroral molecular-emission effects on the atomic oxygen line at 777.4 nm
- 2018
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Ingår i: Earth Planets and Space. - : SPRINGEROPEN. - 1343-8832 .- 1880-5981. ; 70
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Tidskriftsartikel (refereegranskat)abstract
- One of the representative auroral emission lines that radiates from F-region heights and is measurable on the ground is the 777.4nm line from excited atomic oxygen. This line has been adopted, along with another E-region emission line, for example 427.8nm, to estimate the mean energy and total energy flux of precipitating auroral electrons. The influence of emissions from part of the molecular nitrogen band, which mainly radiate from E-region heights, should be carefully evaluated because it might overlap the 777.4nm atomic oxygen line in the spectrum. We performed statistical analysis of auroral spectrograph measurements that were obtained during the winter of 2016-2017 in TromsO, Norway, to derive the ratio of the intensity of the 777.4nm atomic oxygen line to that of the net measurement through a typically used optical filter with a full width at half maximum of a few nm. The ratio had a negative trend against geomagnetic activity, with a primary distribution of 0.5-0.7 and a minimum value of 0.3 for the most active auroral condition in this study. This result suggests that the 30-50% emission intensities measured through the optical filter may be from the molecular nitrogen band.
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