452 research outputs found
A Kinematic Model for the Narrow-Line Region in NGC 4151
We present a simple kinematic model for the narrow-line region (NLR) of the
Seyfert 1 galaxy NGC 4151, based on our previous observations of extended [O
III] emission with the Space Telescope Imaging Spectrograph (STIS). The model
is similar to a biconical radial outflow model developed for the Seyfert 2
galaxy NGC 1068, except that the bicone axis is tilted much more into our line
of sight (40 degrees out of the plane of the sky instead of 5 degrees), and the
maximum space velocities are lower (750 km/s instead of 1300 km/s. We find
evidence for radial acceleration of the emission-line knots to a distance of
160 pc, followed by deceleration that approaches the systemic velocity at a
distance of 290 pc (for a distance to NGC 4151 of 13.3 Mpc). Other similarities
to the kinematics of NGC 1068 are: 1) there are a number of high-velocity
clouds that are not decelerated, suggesting that the medium responsible for the
deceleration is patchy, and 2) the bicone in NGC 4151 is at least partially
evacuated along its axis. Together, these two Seyfert galaxies provide strong
evidence for radial outflow (e.g., due to radiation and/or wind pressure) and
against gravitational motion or expansion away from the radio jets as the
principal kinematic component in the NLR.Comment: 31 pages, Latex, includes 11 figures in postscript, Figures
5a,5b,6a,6b in color, to appear in the Astronomical Journa
The Resolved Narrow Line Region in NGC4151
We present slitless spectra of the Narrow Line Region (NLR) in NGC4151 from
the Space Telescope Imaging Spectrograph (STIS) on HST, and investigate the
kinematics and physical conditions of the emission line clouds in this region.
Using medium resolution (~0.5 Angstrom) slitless spectra at two roll angles and
narrow band undispersed images, we have mapped the NLR velocity field from 1.2
kpc to within 13 pc (H_o=75 km/s/Mpc) of the nucleus. The inner biconical cloud
distribution exhibits recessional velocities relative to the nucleus to the NE
and approaching velocities to the SW of the nucleus. We find evidence for at
least two kinematic components in the NLR. One kinematic component is
characterized by Low Velocities and Low Velocity Dispersions (LVLVD clouds: |v|
< 400 km/s, and Delta_v < 130 km/s). This population extends through the NLR
and their observed kinematics may be gravitationally associated with the host
galaxy. Another component is characterized by High Velocities and High Velocity
Dispersions (HVHVD clouds: 400 130 km/s). This
set of clouds is located within 1.1 arcsec (~70pc) of the nucleus and has
radial velocities which are too high to be gravitational in origin, but show no
strong correlation between velocity or velocity dispersion and the position of
the radio knots. Outflow scenarios will be discussed as the driving mechanism
for these HVHVD clouds.Comment: 38 pages, 14 figures, accepted by ApJ. For higher resolution images
see http://www.pha.jhu.edu/~kaiser
Consistency tests of AMPCALCULATOR and chiral amplitudes in SU(3) Chiral Perturbation Theory: A tutorial based approach
Ampcalculator is a Mathematica based program that was made publicly available
some time ago by Unterdorfer and Ecker. It enables the user to compute several
processes at one-loop (upto ) in SU(3) chiral perturbation theory. They
include computing matrix elements and form factors for strong and non-leptonic
weak processes with at most six external states. It was used to compute some
novel processes and was tested against well-known results by the original
authors. Here we present the results of several thorough checks of the package.
Exhaustive checks performed by the original authors are not publicly available,
and hence the present effort. Some new results are obtained from the software
especially in the kaon odd-intrinsic parity non-leptonic decay sector involving
the coupling . Another illustrative set of amplitudes at tree level we
provide is in the context of -decays with several mesons including quark
mass effects, of use to the BELLE experiment. All eight meson-meson scattering
amplitudes have been checked. Kaon-Compton amplitude has been checked and a
minor error in published results has been pointed out. This exercise is a
tutorial based one, wherein several input and output notebooks are also being
made available as ancillary files on the arXiv. Some of the additional
notebooks we provide contain explicit expressions that we have used for
comparison with established results. The purpose is to encourage users to apply
the software to suit their specific needs. An automatic amplitude generator of
this type can provide error-free outputs that could be used as inputs for
further simplification, and used in varied scenarios such as applications of
chiral perturbation theory at finite temperature, density and volume. This can
also be used by students as a learning aid in low-energy hadron dynamics.Comment: 25 pages, plain latex, corresponds to version to appear in EPJA,
additional ancillary files adde
A junction branch point adjacent to a DNA backbone nick directs substrate cleavage by Saccharomyces cerevisiae Mus81-Mms4
The DNA structure-selective endonuclease Mus81-Mms4/Eme1 incises a number of nicked joint molecule substrates in vitro. 3′-flaps are an excellent in vitro substrate for Mus81-Mms4/Eme1. Mutants in MUS81 are synthetically lethal with mutations in the 5′-flap endonuclease FEN1/Rad27 in Saccharomyces cerevisiae and Schizosaccharomyces pombe. Considering the possibility for isoenergetic interconversion between 3′- and 5′- flaps, these data are consistent with the hypothesis that Mus81-Mms4/Eme1 acts on 3′-flaps in vivo. FEN1/Rad27 prefers dually flapped substrates and cleaves in a way that allows direct ligation of the resulting nick in the product duplex. Here we test the activity of Mus81-Mms4 on dually flapped substrates and find that in contrast to FEN1/Rad27, Mus81-Mms4 activity is impaired on such substrates, resulting in cleavage products that do not allow direct religation. We conclude that Mus81-Mms4, unlike FEN1/Rad27, does not prefer dually flapped substrates and is unlikely to function as a 3′-flapase counterpart to the 5′-flapase activity of FEN1/Rad27. We further find that joint molecule incision by Mus81-Mms4 occurs in a fashion determined by the branch point, regardless of the position of an upstream duplex end. These findings underscore the significance of a nick adjacent to a branch point for Mus81-Mms4 incision
Reduction of astrogliosis and microgliosis by cerebrospinal fluid shunting in experimental hydrocephalus
<p>Abstract</p> <p>Background</p> <p>Reactive gliosis has the potential to alter biomechanical properties of the brain, impede neuronal regeneration and affect plasticity. Determining the onset and progression of reactive astrogliosis and microgliosis due to hydrocephalus is important for designing better clinical treatments.</p> <p>Methods</p> <p>Reactive astrogliosis and microgliosis were evaluated as the severity of hydrocephalus increased with age in hydrocephalic H-Tx rats and control littermates. Previous studies have suggested that gliosis may persist after short-term drainage (shunt treatment) of the cerebrospinal fluid. Therefore shunts were placed in 15d hydrocephalic rats that were sacrificed after 6d (21d of age) or after 21d (36d of age). Tissue was processed for Western blot procedures and immunohistochemistry, and probed for the astrocytic protein, Glial Fibrillary Acidic Protein (GFAP) and for microglial protein, Isolectin B4 (ILB4).</p> <p>Results</p> <p>In the parietal cortex of untreated hydrocephalic animals, GFAP levels increased significantly at 5d and at 12d compared to age-matched control rats. There was a continued increase in GFAP levels over control at 21d and at 36d. Shunting prevented some of the increase in GFAP levels in the parietal cortex. In the occipital cortex of untreated hydrocephalic animals, there was a significant increase over control in levels of GFAP at 5d. This trend continued in the 12d animals, although not significantly. Significant increases in GFAP levels were present in 21d and in 36d animals. Shunting significantly reduced GFAP levels in the 36d shunted group. Quantitative grading of immuno-stained sections showed similar changes in GFAP stained astrocytes.</p> <p>Immuno-stained microglia were altered in shape in hydrocephalic animals. At 5d and 12d, they appeared to be developmentally delayed with a lack of processes. Older 21d and 36d hydrocephalic animals exhibited the characteristics of activated microglia, with thicker processes and enlarged cell bodies. Following shunting, fewer activated microglia were present.</p> <p>Histologic examination of the periventricular area and the periaqueductal area showed similar findings with the 21d and 36d animals having increased populations of both astrocytes and microglia which were reduced following shunting with a more dramatic reduction in the long term shunted animals.</p> <p>Conclusion</p> <p>Overall, these results suggest that reactive astrocytosis and microgliosis are associated with progressive untreated ventriculomegaly, but that shunt treatment can reduce the gliosis occurring with hydrocephalus.</p
Heterologous Overexpression and Mutagenesis of the Human Bile Salt Export Pump (ABCB11) Using DREAM (Directed REcombination-Assisted Mutagenesis)
Homologous recombination in Saccharomyces cerevisiae is a well-studied process. Here, we describe a yeast-recombination-based approach to construct and mutate plasmids containing the cDNA of the human bile salt export pump (BSEP) that has been shown to be unstable in E. coli. Using this approach, we constructed the necessary plasmids for a heterologous overexpression of BSEP in the yeast Pichia pastoris. We then applied a new site-directed mutagenesis method, DREAM (Directed REcombination-Assisted Mutagenesis) that completely bypasses E. coli by using S. cerevisiae as the plasmid host with high mutagenesis efficiency. Finally, we show how to apply this strategy to unstable non-yeast plasmids by rapidly turning an existing mammalian BSEP expression construct into a S. cerevisiae-compatible plasmid and analyzing the impact of a BSEP mutation in several mammalian cell lines
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