960 research outputs found
Ray-tracing in four and higher dimensional black holes: An analytical approximation
We study null rays propagation in a spacetime of static
Schwarzschild--Tangherlini black holes in arbitrary number of dimensions. We
focus on the bending angle and the retarded time delay for rays emitted in the
vicinity of a black hole and propagating to the infinity. We obtain an analytic
expression in terms of elementary functions which approximate the bending angle
and time delay in these spacetimes with high accuracy. We analyze the relative
error of the developed analytic approximations and show that it is quite small
in the complete domain of the parameter space for the rays reaching the
infinity and for different number of the spacetime dimensions. Possible
applications of the obtained results are briefly discussed.Comment: 12 pages, 11 figures, text added to the figures along the abscissa
and ordinate axes, typing errors corrected, some new text added in the main
text also. Accepted for publication in Physical Review
Revealing the Dusty Warm Absorber in MCG--6-30-15 with the Chandra HETG
We present detailed evidence for a warm absorber in the Seyfert 1 galaxy
MCG--6-30-15 and dispute earlier claims for relativistic O line emission. The
HETG spectra show numerous narrow, unresolved (FWHM < 200 km/s) absorption
lines from a wide range of ionization states of N, O, Mg, Ne, Si, S, Ar, and
Fe. The O VII edge and 1s^2--1snp resonance line series to n=9 are clearly
detected at rest in the AGN frame. We attribute previous reports of an
apparently highly redshifted O VII edge to the 1s^2--1snp (n > 5) O VII
resonance lines, and a neutral Fe L absorption complex. The shape of the Fe L
feature is nearly identical to that seen in the spectra of several X-ray
binaries, and in laboratory data. The implied dust column density agrees with
that obtained from reddening studies, and gives the first direct X-ray evidence
for dust embedded in a warm absorber. The O VIII resonance lines and weak edge
are also detected, and the spectral rollover below 2 keV is explained by the
superposition of numerous absorption lines and edges. We identify, for the
first time, a KLL resonance in the O VI photoabsorption cross section, giving a
measure of the O VI column density. The O VII (f) emission detected at the
systemic velocity implies a covering fraction of ~5% (depending on the observed
vs. time-averaged ionizing flux). Our observations show that a dusty warm
absorber model is not only adequate to explain all the spectral features > 0.48
keV (< 26 \AA) the data REQUIRE it. This contradicts the interpretation of
Branduardi-Raymont et al. (2001) that this spectral region is dominated by
highly relativistic line emission from the vicinity of the black hole.Comment: 4.5 pages, 1 color figure, accepted (April 2001) for publication in
ApJL, not many changes from the initial submission - updated/added some
measuements for the O VII resonance series, and added a discussion about FeO2
grain
The Role of Diffusive Shock Acceleration on Nonequilibrium Ionization in Supernova Remnant Shocks II: Emitted Spectra
We present a grid of nonequilibrium ionization models for the X-ray spectra
from supernova remnants undergoing efficient diffusive shock acceleration. The
calculation follows the hydrodynamics of the blast wave as well as the
time-dependent ionization of the plasma behind the shock. The ionization state
is passed to a plasma emissivity code to compute the thermal X-ray emission,
which is combined with the emission from nonthermal synchrotron emission to
produce a self-consistent model for the thermal and nonthermal emission from
cosmic-ray dominated shocks. We show how plasma diagnostics such as the
G'-ratio of He-like ions, defined as the ratio of the sum of the
intercombination, forbidden, and satellite lines to the resonance line, can
vary with acceleration efficiency, and discuss how the thermal X-ray emission,
when the time-dependent ionization is not calculated self-consistently with the
hydrodynamics, can differ from the thermal X-ray emission from models which do
account for the hydrodynamics. Finally we compare the thermal X-ray emission
from models which show moderate acceleration (~ 35%) to the thermal X-ray
emission from test-particle models.Comment: 17 pages, 12 figures. accepted for publication in the Astrophysical
Journa
Transplantation of Human Neuroblastoma Cells, Catecholaminergic and Non-Catecholaminergic: Effects on Rotational Behavoir in Parkinson's Rat Model
Cultured human catecholaminergic and noncatecholaminergic
donor cells were used in
neural transplantation experiments in a rat
model of Parkinson's disease. Using two different
human catecholaminergic neuroblastoma cell
lines, one control non-catecholaminergic neuroblastoma
cell line, and one sham control (tissue
culture medium), transplants were made into the
striatum using a modified Ungerstedt
hemiparkinsonian rat model. Significant
decreases in apomorphine-induced rotational
behavior were produced by two of three
catecholaminergic cell lines. Grafted cells staining
positively for tyrosine hydroxylase (TH) and
catecholamine fluorescence indicated viable catecholamine
activity in the two cell lines which produced
reductions in rotational behavior.
Catecholamine fluorescence was not detected in
either of the two controls. These data suggest a
link between catecholamine secretion by transplanted
cells and motor improvement using a rat
rotational behavior model
Shocked Molecular Hydrogen in the 3C 326 Radio Galaxy System
The Spitzer spectrum of the giant FR II radio galaxy 3C 326 is dominated by
very strong molecular hydrogen emission lines on a faint IR continuum. The H2
emission originates in the northern component of a double-galaxy system
associated with 3C 326. The integrated luminosity in H2 pure-rotational lines
is 8.0E41 erg/s, which corresponds to 17% of the 8-70 micron luminosity of the
galaxy. A wide range of temperatures (125-1000 K) is measured from the H2 0-0
S(0)-S(7) transitions, leading to a warm H2 mass of 1.1E9 Msun. Low-excitation
ionic forbidden emission lines are consistent with an optical LINER
classification for the active nucleus, which is not luminous enough to power
the observed H2 emission. The H2 could be shock-heated by the radio jets, but
there is no direct indication of this. More likely, the H2 is shock-heated in a
tidal accretion flow induced by interaction with the southern companion galaxy.
The latter scenario is supported by an irregular morphology, tidal bridge, and
possible tidal tail imaged with IRAC at 3-9 micron. Unlike ULIRGs, which in
some cases exhibit H2 line luminosities of comparable strength, 3C 326 shows
little star-formation activity (~0.1 Msun/yr). This may represent an important
stage in galaxy evolution. Starburst activity and efficient accretion onto the
central supermassive black hole may be delayed until the shock-heated H2 can
kinematically settle and coolComment: 27 pages, 7 figures, accepted for publication in the Astrophysical
Journa
Bandwidth considerations in modulated and transient photoconductivity measurements to determine localized state distributions
This work examines the influence of limited instrumental bandwidth on the accuracy of recovery of the density of localized states in semiconductors from transient and modulated photoconductivity data. Paradoxically, knowledge of the short-time transient photoresponse can be vital in the estimation, via a Fourier transform, of the density of deep-lying states. We demonstrate that retention of the natural response of a bandwidth limited system, although subject to distortion at short times, can lead to much improved accuracy in density of states determination than simple truncation of the short-time response. It is shown that this improvement arises simply from the integrating effect of a bandwidth limited system over short time intervals, which makes it possible to access and exploit information originating at times much shorter than the instrumentation rise time. These concepts are exemplified using computer simulated transient photoconductivity for several model systems including one which mimics the expected density of states in amorphous silicon
Transcriptomic profiling of 39 commonly-used neuroblastoma cell lines
Neuroblastoma cell lines are an important and cost-effective model used to study oncogenic drivers of the disease. While many of these cell lines have been previously characterized with SNP, methylation, and/or mRNA expression microarrays, there has not been an effort to comprehensively sequence these cell lines. Here, we present raw whole transcriptome data generated by RNA sequencing of 39 commonly-used neuroblastoma cell lines. These data can be used to perform differential expression analysis based on a genetic aberration or phenotype in neuroblastoma (e.g., MYCN amplification status, ALK mutation status, chromosome arm 1p, 11q and/or 17q status, sensitivity to pharmacologic perturbation). Additionally, we designed this experiment to enable structural variant and/or long-noncoding RNA analysis across these cell lines. Finally, as more DNase/ATAC and histone/transcription factor ChIP sequencing is performed in these cell lines, our RNA-Seq data will be an important complement to inform transcriptional targets as well as regulatory (enhancer or repressor) elements in neuroblastoma
Intrinsic Absorption in the Spectrum of NGC 7469: Simultaneous Chandra, FUSE, and STIS Observations
We present simultaneous X-ray, far-ultraviolet, and near-ultraviolet spectra
of the Seyfert 1 galaxy NGC 7469 obtained with the Chandra X-Ray Observatory,
the Far Ultraviolet Spectroscopic Explorer, and the Space Telescope Imaging
Spectrograph on the Hubble Space Telescope. Previous non-simultaneous
observations of this galaxy found two distinct UV absorption components, at
-560 and -1900 km/s, with the former as the likely counterpart of the X-ray
absorber. We confirm these two absorption components in our new UV
observations, in which we detect prominent O VI, Ly alpha, N V, and C IV
absorption. In our Chandra spectrum we detect O VIII emission, but no
significant O VIII or O VII absorption. We also detect a prominent Fe K alpha
emission line in the Chandra spectrum, as well as absorption due to
hydrogen-like and helium-like neon, magnesium, and silicon at velocities
consistent with the -560 km/s UV absorber. The FUSE and STIS data reveal that
the H I and C IV column densities in this UV- and X-ray- absorbing component
have increased over time, as the UV continuum flux decreased. We use measured H
I, N V, C IV, and O VI column densities to model the photoionization state of
both absorbers self-consistently. We confirm the general physical picture of
the outflow in which the low velocity component is a highly ionized, high
density absorber with a total column density of 10^20 cm^-2, located near the
broad emission line region, although due to measurable columns of N V and C IV,
we assign it a somewhat smaller ionization parameter than found previously,
U~1. The high velocity UV component is of lower density, log N=18.6, and likely
resides farther from the central engine as we find its ionization parameter to
be U=0.08.Comment: Minor correction to abstract; STScI eprint #1683; 50 pages, incl. 19
figures, 4 tables; Accepted to Ap
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Cx3cr1-deficient microglia exhibit a premature aging transcriptome.
CX3CR1, one of the highest expressed genes in microglia in mice and humans, is implicated in numerous microglial functions. However, the molecular mechanisms underlying Cx3cr1 signaling are not well understood. Here, we analyzed transcriptomes of Cx3cr1-deficient microglia under varying conditions by RNA-sequencing (RNA-seq). In 2-mo-old mice, Cx3cr1 deletion resulted in the down-regulation of a subset of immune-related genes, without substantial epigenetic changes in markers of active chromatin. Surprisingly, Cx3cr1-deficient microglia from young mice exhibited a transcriptome consistent with that of aged Cx3cr1-sufficient animals, suggesting a premature aging transcriptomic signature. Immunohistochemical analysis of microglia in young and aged mice revealed that loss of Cx3cr1 modulates microglial morphology in a comparable fashion. Our results suggest that CX3CR1 may regulate microglial function in part by modulating the expression levels of a subset of inflammatory genes during chronological aging, making Cx3cr1-deficient mice useful for studying aged microglia
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