247 research outputs found
X-ray and optical variability of Seyfert 1 galaxies as observed with XMM-Newton
We have examined simultaneous X-ray and optical light curves of a sample of
eight nearby Seyfert 1 galaxies observed using the EPIC X-ray cameras and
Optical Monitor on board XMM. The observations span ~1 day and revealed optical
variability in four of the eight objects studied. In all cases, the X-ray
variability amplitude exceeded that of the optical both in fractional and
absolute luminosity terms. No clearly significant correlations were detected
between wavebands using cross correlation analysis. We conclude that, in three
of the four objects in which optical variability was detected, reprocessing
mechanisms between wavebands do not dominate either the optical or X-ray
variability on the time-scales probed.Comment: 9 pages, 2 figures, accepted for publication in MNRA
Optical Monitoring of 3C 390.3 from 1995 to 2004 and Possible Periodicities in the Historical Light Curve
We report V, R, and I band CCD photometry of the radio galaxy 3C 390.3
obtained with the 1.56-m telescope of the Shanghai Astronomical Observatory
from March 1995 to August 2004. Combining these data with data from the
literature, we have constructed a historical light curve from 1894 to 2004 and
searched for periodicities using the CLEANest program. We find possible periods
of 8.30+-1.17, 5.37+-0.49, 3.51+-0.21, and 2.13+-0.08 years.Comment: Accepted by AJ, 34 pages, 11 figure
A Multi-Wavelength Study of the Nature of Type 1.8/1.9 Seyfert Galaxies
We focus on determining the underlying physical cause of a Seyfert galaxy's
appearance as type a 1.8 or 1.9. Are these "intermediate" Seyfert types typical
Seyfert 1 nuclei with reddened broad-line regions? Or are they objects with
intrinsically weak continua and broad emission lines? We compare measurements
of the optical reddening of the narrow and broad-line regions with each other
and with the X-ray column derived from XMM-Newton 0.5-10 keV spectra to
determine the presence and location of dust in the line of sight. We also
searched the literature to see if the objects showed evidence for broad-line
variability, and determined if the changes were consistent with a change in
reddening or a change in the intrinsic ionizing continuum flux. We find that 10
of 19 objects previously classified as Seyfert 1.8/1.9s received this
designation due to their low continuum flux. In four objects the classification
was due to BLR reddening, either by the torus or dust structures in the
vicinity of the NLR; in the remaining five objects there is not sufficient
evidence to favor one scenario over the other. These findings imply that, in
general, samples of 1.8/1.9s are not suitable for use in studies of the gas and
dust in the central torus.Comment: 85 pages, accepted by Ap
Hammering K-wires is Superior to Drilling with Irrigation
Cooling during drilling Kirschner wires is not always effective in preventing thermal related damage. In this study, we used a human in vitro model and compared temperature elevation, insertion time, and extraction force between three Kirschner wire insertion methodsâdrilling with and without irrigation and pneumatic hammering. Forty five Kirschner wires were inserted into 15 fresh human cadaver metacarpals. All three insertion methods were applied in each metacarpal. Drilling without irrigation resulted in a temperature elevation of 67.25â±â5.4âÂșC with significantly lower values for drilling with irrigation (4.15â±â0.6âÂșC) and pneumatic hammering (31.52â±â3.4âÂșC). The insertion time for pneumatic hammering (47.63â±â8.8 s) was significantly lower compared to drilling without irrigation (263.16â±â36.5 s) and drilling with irrigation (196.10â±â28.5 s). Extraction forces after drilling without irrigation, drilling with irrigation, and pneumatic hammering were 39.85â±â4.1 N, 57.81â±â6.5 N, and 62.23â±â6.7 N, respectively. Pneumatic hammering is superior to drilling without irrigation, especially when irrigation is not possible
The CaT strength in Seyfert nuclei revisited: analyzing young stars and non-stellar light contributions to the spectra
In a former paper (Garcia-Rissmann et al. 2005; hereafter Paper I), we have
presented spectra of 64 active, 9 normal and 5 Starburst galaxies in the region
around the near-IR Calcium triplet absorption lines and the [SIII]9069 line. In
the present paper we analyze the CaT strength (WCaT), and kinematical products
derived in that study, namely stellar and ionized gas velocity dispersions. Our
main results may be summarized as follows: (1) Seyfert 2s show no sign of
dilution in WCaT with respect to the values spanned by normal galaxies, even
when optical absorption lines such as the CaII K band at 3933 A are much weaker
than in old, bulge-like stellar populations. (2) The location of Seyfert 2s in
the WCaT-WCaK plane is consistent with evolutionary synthesis models. The
implication is that the source responsible for the dilution of optical lines in
these AGN is a young stellar population, rather than an AGN featureless
continuum, confirming the conclusion of the pioneer study of Terlevich, Diaz &
Terlevich. (3) In Seyfert 1s, both W[SIII] and WCaT tend to be diluted due to
the presence of a non-stellar component, in agreement with the unification
paradigm. (4) A comparison of stellar and gas velocity dispersions confirms the
existence of a correlation between the typical velocities of stars and clouds
of the Narrow Line Region. The strength and scatter around this correlation are
similar to those previously obtained from the [OIII]5007 line width.Comment: 14 pages, 15 figures. Paper accepted for publication in MNRA
A central cavity within the holo-translocon suggests a mechanism for membrane protein insertion.
The conserved SecYEG protein-conducting channel and the accessory proteins SecDF-YajC and YidC constitute the bacterial holo-translocon (HTL), capable of protein-secretion and membrane-protein insertion. By employing an integrative approach combining small-angle neutron scattering (SANS), low-resolution electron microscopy and biophysical analyses we determined the arrangement of the proteins and lipids within the super-complex. The results guided the placement of X-ray structures of individual HTL components and allowed the proposal of a model of the functional translocon. Their arrangement around a central lipid-containing pool conveys an unexpected, but compelling mechanism for membrane-protein insertion. The periplasmic domains of YidC and SecD are poised at the protein-channel exit-site of SecY, presumably to aid the emergence of translocating polypeptides. The SecY lateral gate for membrane-insertion is adjacent to the membrane 'insertase' YidC. Absolute-scale SANS employing a novel contrast-match-point analysis revealed a dynamic complex adopting open and compact configurations around an adaptable central lipid-filled chamber, wherein polytopic membrane-proteins could fold, sheltered from aggregation and proteolysis
On the cosmic evolution of the scaling relations between black holes and their host galaxies: Broad Line AGN in the zCOSMOS survey
(Abriged) We report on the measurement of the rest frame K-band luminosity
and total stellar mass of the hosts of 89 broad line Active Galactic Nuclei
detected in the zCOSMOS survey in the redshift range 1<z<2.2. The unprecedented
multiwavelength coverage of the survey field allows us to disentangle the
emission of the host galaxy from that of the nuclear black hole in their
Spectral Energy Distributions. We derive an estimate of black hole masses
through the analysis of the broad Mg II emission lines observed in the
medium-resolution spectra taken with VIMOS/VLT as part of the zCOSMOS project.
We found that, as compared to the local value, the average black hole to host
galaxy mass ratio appears to evolve positively with redshift, with a best fit
evolution of the form (1+z)^{0.68 \pm0.12 +0.6 -0.3}, where the large
asymmetric systematic errors stem from the uncertainties in the choice of IMF,
in the calibration of the virial relation used to estimate BH masses and in the
mean QSO SED adopted. A thorough analysis of observational biases induced by
intrinsic scatter in the scaling relations reinforces the conclusion that an
evolution of the MBH-M* relation must ensue for actively growing black holes at
early times: either its overall normalization, or its intrinsic scatter (or
both) appear to increase with redshift. This can be interpreted as signature of
either a more rapid growth of supermassive black holes at high redshift, a
change of structural properties of AGN hosts at earlier times, or a significant
mismatch between the typical growth times of nuclear black holes and host
galaxies.Comment: 47 pages, 8 figures. Accepted for publication in Ap
The X-Ray Variability of a Large, Serendipitous Sample of Spectroscopic Quasars
We analyze the X-ray variability of 264 Sloan Digital Sky Survey
spectroscopic quasars using the Chandra public archive. This data set consists
of quasars with spectroscopic redshifts out to z~5 and covers rest-frame time
scales up to Delta t_sys 2000 d, with 3 or more X-ray observations available
for 82 quasars. It therefore samples longer time scales and higher luminosities
than previous large-scale analyses of AGN variablity. We find significant (>3
sigma) variation in ~30% of the quasars overall; the fraction of sources with
detected variability increases strongly with the number of available source
counts up to ~70% for sources with >1000 counts per epoch. Assuming the
distribution of fractional variation is Gaussian, its standard deviation is
~16% on >1 week time scales, which is not enough to explain the observed
scatter in quasar X-ray-to-optical flux ratios as due to variability alone. We
find no evidence in our sample that quasars are more variable at higher
redshifts (z > 2), as has been suggested in previous studies. Quasar X-ray
spectra vary similarly to some local Seyfert AGN in that they steepen as they
brighten, with evidence for a constant, hard spectral component that is more
prominent in fainter stages. We identify one highly-variable Narrow Line
Seyfert 1-type spectroscopic quasar in the Chandra Deep Field-North. We
constrain the rate of kilosecond-timescale flares in the quasar population
using ~8 months of total exposure and also constrain the distribution of
variation amplitudes between exposures; extreme changes (>100%) are quite rare,
while variation at the 25% level occurs in <25% of observations. [OIII] 5007A
emission may be stronger in sources with lower levels of X-ray variability; if
confirmed, this would represent an additional link between small-scale (corona)
and large-scale (narrow line region) AGN properties.Comment: Submitted to Ap
Systems biology approaches applied to regenerative medicine
Systems biology is the creation of theoretical and mathematical models for the study of biological systems, as an engine for hypothesis generation and to provide context to experimental data. It is underpinned by the collection and analysis of complex datasets from different biological systems, including global gene, RNA, protein and metabolite profiles. Regenerative medicine seeks to replace or repair tissues with compromised function (for example, through injury, deficiency or pathology), in order to improve their functionality. In this paper, we will address the application of systems biology approaches to the study of regenerative medicine, with a particular focus on approaches to study modifications to the genome, transcripts and small RNAs, proteins and metabolites
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