Results 1 - 10 of 10600
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[en] The measurement of vacuum ultraviolet spectra (500-2000A) from a target plasma device is described. The plasma spectra, impurities, impurity sources and radiation mechanism of plasma gun are analysed
[en] Spatial heterodyne spectrographs combine high spectral resolution with large etendue in a compact instrument. This combination makes them useful for studies of extended diffuse sources requiring velocity resolution or the separation of closely packed emission lines, while their small size makes them suitable for platforms ranging from ground-based observatories to satellites. Improvements in optical element and detector capabilities have expanded opportunities for SHS in the VUV, where its combination of size, resolution, and etendue have not been available. Here we discuss the basics of the SHS technique and how an instrument may be designed to study various emission line sources in the solar system
[en] We re-examine the physical relationship between extreme ultraviolet (EUV) waves and type II radio bursts. It has been thought that they are two observational aspects of a single coronal shock wave. However, a lack of their speed correlation hampers the understanding of their respective (or common) natures in a single phenomenon. Knowing the uncertainties in identifying true wave components from observations and measuring their speeds, we re-examine the speeds of EUV waves reported in previous literature and compare these with type II radio bursts and coronal mass ejections (CMEs). This confirms the inconsistency between the speeds of EUV waves and their associated type II radio bursts. Second, CME speeds are found to have a better correlation with type II radio bursts than EUV waves. Finally, type II speeds and their range tend to be much greater than those of EUV waves. We demonstrate that the speed inconsistency is in fact an intrinsic tendency and elucidate the nature of a coronal shock wave consisting of both driven and non-driven parts. This suggests that the speed inconsistency would remain even if all other uncertainties were removed.
[en] In this study, we investigate an extreme ultraviolet (EUV) wave event on 2010 February 11, which occurred as a limb event from the Earth viewpoint and a disk event from the Solar Terrestrial Relations Observatory-Behind viewpoint. We use the data obtained by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory in various EUV channels. The EUV wave event was launched by a partial prominence eruption. Compared with some EUV wave events in previous works, this EUV wave event contains a faster wave with a speed of ∼445 ± 6 km s−1, which we call a coronal Moreton wave, and a slower wave with a speed of ∼298 ± 5 km s−1, which we call the Extreme Ultraviolet Imaging Telescope (EIT) wave. The coronal Moreton wave is identified as a fast-mode wave and the EIT wave is identified as an apparent propagation due to successive field-line stretching. We also observe a stationary front associated with the fast-mode EUV wave. This stationary front is explained as mode conversion from the coronal Moreton wave to a slow-mode wave near a streamer.
[en] Spark gap triggering with laser unltraviolet radiation (λ=308 nm) transmitted through a light guide is studied. In laser plasma production on tantalum cathode spark gap initiation delay time is ∼ 10 ns and initiation instability - ≤ 1 ns
[en] Experimental and theoretical spectroscopic methods have been combined to disentangle the fundamental mechanism of VUV induced fragmentation of the three isomers of nitroimidazole radiosensitisers. (paper)
[en] The extreme outer Galaxy (EOG), the region with a Galactic radius of more than 18 kpc, is known to have a very low metallicity, about one-tenth that of the solar neighborhood. We obtained the deep near-infrared (NIR) images of two very young (∼0.5 Myr) star-forming clusters that are two of the most distant embedded clusters in the EOG. We find that in both clusters the fraction of stars with NIR excess, which originates from the circumstellar dust disk at radii of ≤0.1 AU, is significantly lower than those in the solar neighborhood. Our results suggest that most of the stars forming in the low-metallicity environment experience disk dispersal at an earlier stage (<1 Myr) than those forming in the solar metallicity environment (as much as ∼5-6 Myr). Such a rapid disk dispersal may make the formation of planets difficult, and the shorter disk lifetime with a lower metallicity, could contribute to the strong metallicity dependence of the well-known 'planet-metallicity correlation', which states that the probability of a star hosting a planet increases steeply with stellar metallicity. The reason for the rapid disk dispersal could be the increase of the mass accretion rate and/or the effective far-ultraviolet photoevaporation due to the low extinction; however, another unknown mechanism for the EOG environment could be contributing significantly.