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Bending and Breathing Modes of the Galactic Disk
We explore the hypothesis that a passing satellite or dark matter subhalo has
excited coherent oscillations of the Milky Way's stellar disk in the direction
perpendicular to the Galactic midplane. This work is motivated by recent
observations of spatially dependent bulk vertical motions within ~ kpc of the
Sun. A satellite can transfer a fraction of its orbital energy to the disk
stars as it plunges through the Galactic midplane thereby heating and
thickening the disk. Bulk motions arise during the early stages of such an
event when the disk is still in an unrelaxed state. We present simple toy-model
calculations and simulations of disk-satellite interactions, which show that
the response of the disk depends on the relative velocity of the satellite.
When the component of the satellite's velocity perpendicular to the disk is
small compared with that of the stars, the perturbation is predominantly a
bending mode. Conversely, breathing and higher order modes are excited when the
vertical velocity of the satellite is larger than that of the stars. We argue
that the compression and rarefaction motions seen in three different surveys
are in fact breathing mode perturbations of the Galactic disk.Comment: 12 pages, 12 figure
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Synergistic Anti-Candida Activity of Bengazole A in the Presence of Bengamide A †.
Bengazoles A⁻G from the marine sponge Jaspis sp. exhibit potent in vitro antifungal activity against Candida spp. and other pathogenic fungi. The mechanism of action (MOA) of bengazole A was explored in Candida albicans under both liquid culture and surface culture on Mueller-Hinton agar. Pronounced dose-dependent synergistic antifungal activity was observed with bengazole A in the presence of bengamide A, which is also a natural product from Jaspis sp. The MOA of bengazole A was further explored by monitoring the sterol composition of C. albicans in the presence of sub-lethal concentrations of bengazole A. The GCMS of solvent extracts prepared from liquid cultures of C. albicans in the presence of clotrimazole-a clinically approved azole antifungal drug that suppresses ergosterol biosynthesis by the inhibition of 14α-demethylase-showed reduced cellular ergosterol content and increased concentrations of lanosterol and 24-methylenedihydrolanosterol (a shunt metabolite of ergosterol biosynthesis). No change in relative sterol composition was observed when C. albicans was cultured with bengazole A. These results eliminate an azole-like MOA for the bengazoles, and suggest that another as-yet unidentified mechanism is operative
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