5,484 research outputs found
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Stardust microcrater residue compositional groups
Compositional groups are defined in residue from Stardust craters (1-9 Dc) by qualitative EDS. These compositional groups are being further studied by a FIB-SEM technique to determine representative residue compositions
Limiting stable currents in bounded electron and ion streams
The classical static analysis of the infinite planar diode has been extended to include the effects of finite transverse beam size. Simple expressions have been found for the increase in maximum stable current density over that of an infinite stream for finite cylindrical and strip streams flowing between plates of infinite diodes. The results are also given in terms of stream perveance. The effect of a nonuniform distribution of current across the stream is shown to be relatively small. Experimental values of maximum stable current agree with those obtained from the analysis. A further extension of the static analysis has been made to include the effects of additional conducting plane boundaries parallel to the stream motion. For length-to-width ratios L/D less than 0.25 the tube is adequately described by the results for the infinite planar diode and for L/D greater than 4, the infinitely-long drift tube theory suffices. At intermediate values of L/D, the maximum amount of current that can be stably passed through the tube is greater than that predicted by either asymptotic theory
B-R Colors of Globular Clusters in NGC 6166 (A2199)
We have analysed new R-band photometry of globular clusters in NGC 6166, the
cD galaxy in the cooling flow cluster A2199. In combination with the earlier B
photometry of Pritchet \& Harris (1990), we obtain BR colours for 40
globular clusters in NGC 6166. The mean BR is 1.26 0.11, corresponding
to a mean [Fe/H] = 1 0.4. Given that NGC 6166 is one of the most
luminous cD galaxies studied to date, our result implies significant scatter in
the relationship between mean cluster [Fe/H] and parent galaxy luminosity. We
obtain a globular cluster specific frequency of S 9, with a possible
range between 5 and 18. This value is inconsistent with the value of S
4 determined earlier by Pritchet \& Harris (1990) from B-band
photometry, and we discuss possible reasons for the discrepancy. Finally, we
reassess whether or not cooling flows are an important mechanism for forming
globular clusters in gE/cD galaxies.Comment: 8 pages, uuencoded, gzipped tar file with latex file, 6 figures (Fig
1 omitted because of size), and mn.sty file. Figures will be embedded into
the postscript file. Accepted (March 1996) for publication in MNRA
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The rocks from space initiative and the space safari
This paper reports the successes of a new initiative in the UK using electronic resources, such as virtual learning environments and e-classrooms, for planetary and space science public engagement activities
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Iron Oxide Grains in Stardust Track 121 Grains as Evidence of Comet Wild 2 Hydrothermal Alteration
Stardust Track 121 terminal grains contain Fe-oxide. These are consistent with the presence of hydrothermal alteration on the Comet Wild 2 parent body
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Geochemical Endmembers preserved in Gale Crater: A tale of two mudstones and their compositional differences according to ChemCam
Gale crater contains two fine-grained mudstone sedimentary units: The Sheepbed mudstone member, and the Murray formation mud-stones. These mudstones formed as part of an ancient fluviolacustrine system. The NASA Curiosity rover has analysed these mudstone units using the Chemistry and Camera (ChemCam), Alpha Particle X-ray Spectrometer (APXS) and Chemistry and Mineralogy (CheMin) onboard instrument suites. Subsequent mineralogical analyses have uncovered a wide geochemical and mineralogical diversity across and within these two mudstone formations. This study aims to determine the principal cause (alteration or source region) of this geochemical variation through a statistical analysis of the ChemCam dataset up to sol 1482, including the lower to middle Murray formation
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Geochemical Endmembers preserved in the fluviolacustrine sediments of Gale crater
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