4,678 research outputs found
Black Holes and Galactic Density Cusps Spherically Symmetric Anisotropic Cusps
Aims: In this paper we study density cusps that may contain central black
holes. The actual co-eval self-similar growth would not distinguish between the
central object and the surroundings. Methods: To study the environment of a
growing black hole we seek descriptions of steady `cusps' that may contain a
black hole and that retain at least a memory of self-similarity. We refer to
the environment in brief as the `bulge' and on smaller scales, the `halo'.
Results: We find simple descriptions of the simulations of collisionless matter
by comparing predicted densities, velocity dispersions and distribution
functions with the simulations. In some cases central point masses may be
included by iteration. We emphasize that the co-eval self-similar growth allows
an explanation of the black hole bulge mass correlation between approximately
similar collisionless systems. Conclusions: We have derived our results from
first principles assuming adiabatic self-similarity and either self-similar
virialisation or normal steady virialisation. We conclude that distribution
functions that retain a memory of self-similar evolution provide an
understanding of collisionless systems. The implied energy relaxation of the
collisionless matter is due to the time dependence. Phase mixing relaxation may
be enhanced by clump-clump interactions.Comment: 9 pp, 3 figs, accepted by A\&
Rapid rotation of micron and submicron dielectric particles measured using optical tweezers
We demonstrate the use of a laser trap (âoptical tweezersâ) and back-focal-plane position detector to measure rapid rotation in aqueous solution of single particles with sizes in the vicinity of 1 ÎŒm. Two types of rotation were measured: electrorotation of polystyrene microspheres and rotation of the flagellar motor of the bacterium Vibrio alginolyticus. In both cases, speeds in excess of 1000 Hz (rev sâ1) were measured. Polystyrene beads of diameter about 1 ÎŒm labelled with smaller beads were held at the centre of a microelectrode array by the optical tweezers. Electrorotation of the labelled beads was induced by applying a rotating electric field to the solution using microelectrodes. Electrorotation spectra were obtained by varying the frequency of the applied field and analysed to obtain the surface conductance of the beads. Single cells of V. alginolyticus were trapped and rotation of the polar sodium-driven flagellar motor was measured. Cells rotated more rapidly in media containing higher concentrations of Na+, and photodamage caused by the trap was considerably less when the suspending medium did not contain oxygen. The technique allows single-speed measurements to be made in less than a second and separate particles can be measured at a rate of several per minute
The Gravitational Lens Candidate FBQ 1633+3134
We present our ground-based optical imaging, spectral analysis, and high
resolution radio mapping of the gravitational lens candidate FBQ 1633+3134.
This z=1.52, B=17.7 quasar appears double on CCD images with an image
separation of 0.66 arcseconds and a flux ratio of ~3:1 across BVRI filters. A
single 0.27 mJy radio source is detected at 8.46 GHz, coincident to within an
arcsecond of both optical components, but no companion at radio wavelengths is
detected down to a flux level of 0.1 mJy (3 sigma). Spectral observations
reveal a rich metal-line absorption system consisting of a strong Mg II doublet
and associated Fe I and Fe II absorption features, all at an intervening
redshift of z=0.684, suggestive of a lensing galaxy. Point spread function
subtraction however shows no obvious signs of a third object between the two
quasar images, and places a detection limit of I > 23.0 if such an object
exists. Although the possibility that FBQ 1633+3134 is a binary quasar cannot
be ruled out, the evidence is consistent with it being a single quasar lensed
by a faint, metal-rich galaxy.Comment: 24 pages, 5 figures. Accepted by AJ. A calibration error affecting B
and V band apparent magnitudes has been corrected. The conclusions of the
paper are not change
Stimulation of NSF ATPase activity during t-SNARE priming
AbstractN-Ethylmaleimide-sensitive factor (NSF) plays a key role in vesicular traffic by disassembling and priming SNARE proteins for their function in docking and fusion. We demonstrate that the ATPase activity of NSF is activated by α-soluble NSF attachment protein (α-SNAP) in a complex with syntaxin 1A. In addition, we show that a construct consisting of the H3 domain of syntaxin 1A (GST-synt(195â263), which does not support NSF disassembly in the presence of MgATP gave a larger stimulation. NSF ATPase activation was specific and did not occur using mutant α-SNAPs unable to bind GST-synt or with mutated C-termini. We suggest that activation of NSF ATPase activity in the SNARE complex may be essential to allow SNARE priming
Hubble Space Telescope Images of Magellanic Cloud Planetary Nebulae
We present images and slitless spectra which were obtained in HST surveys of
Planetary Nebulae (PNe) in both the Large and Small Magellanic Clouds, using
the Space Telescope Imaging Spectrograph. These new data on 59 PNe (54 in the
LMC and five in the SMC) permit us to determine the nebular dimensions and
morphology in the monochromatic light of several emission lines: Halpha, [N II]
lambda 6583 and [O III] lambda 5007, plus others of varying ionization,
including [O I], He I, and [S II]. We describe the nebular morphology and
related features in detail. This survey, when combined with similar data from
our prior HST programs and other archived PN images, brings the total of
nebulae imaged with HST to 114 in the LMC and 35 in the SMC. We describe
various basic properties for the sample, including sizes, morphologies,
densities, and completeness. Trends in [O III] lambda 5007 flux, surface
brightness, and electron density with physical radius suggest that many
nebulae, particularly those with bipolar morphology, may be optically thick
even at large size. Bipolars also show the most extreme values of [N II]/Halpha
flux ratios, which is a rough indicator N enrichment.Comment: Accepted for publication in the Astrophysical Journal, 65 pages, 26
figures, 6 tables. For a high resolution version of Figs 4 to 19, see
http://archive.stsci.edu/hst/mcpn/home.htm
RETROCAM: A Versatile Optical Imager for Synoptic Studies
We present RETROCAM, an auxiliary CCD camera that can be rapidly inserted
into the optical beam of the MDM 2.4m telescope. The speed and ease of
reconfiguring the telescope to use the imager and a straightforward user
interface permit the camera to be used during the course of other observing
programs. This in turn encourages RETROCAM's use for a variety of monitoring
projects.Comment: 6 pages, 6 figures, Accepted by A
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