266 research outputs found
Use of Nuclear Magnetic Resonance Imaging Angiography to Follow-Up Arterial Remodeling in an Animal Model
Appropriately sized arteries in small animals may be possible models for studying the remodeling process as occurs after arterial balloon injury in humans. Magnetic resonance imaging (MRI) is able to noninvasively image tissue in vivo. To date, small animal angiog raphy models have mostly used research-dedicated instruments and resolution, which are not universally available.Experiments were carried out on a rat aorta model of remodeling in vivo (n=40). Arteries were injured by oversized balloon dilation; control arteries were uninjured. Angiography imaging was performed immediately before sacrifice with an unmodified clinical MRI unit, a 1.5 Tesla MR tomograph with a 20-cm-diameter coil. Longitudinal MRI pictures of the aorta and morphometry of tissue sections to measure luminal and arterial wall areas were analyzed with use of computer-assisted techniques.Comparison of dimensions demonstrated correlation between MRI and histology measurements of the lumen. MRI and morphometry showed a gradual increase in mean luminal area over 6 weeks following injury. The lumen increase correlated with total arterial area and thickness.In this rat aorta model, remodeling documented at histology was followed-up in vivo. The use of such clinical MRI scanners has potential to reduce animal numbers needed to follow-up the remodeling process after therapeutic intervention
The MRO-accompanied modes of Re-implantation into SiO2-host matrix: XPS and DFT based scenarios
The following scenarios of Re-embedding into SiO2-host by pulsed
Re-implantation were derived and discussed after XPS-and-DFT electronic
structure qualification: (i) low Re-impurity concentration mode -> the
formation of combined substitutional and interstitial impurities with
Re2O7-like atomic and electronic structures in the vicinity of oxygen
vacancies; (ii) high Re-impurity concentration mode -> the fabrication of
interstitial Re-metal clusters with the accompanied formation of ReO2-like
atomic structures and (iii) an intermediate transient mode with Re-impurity
concentration increase, when the precursors of interstitial defect clusters are
appeared and growing in the host-matrix structure occur. An amplification
regime of Re-metal contribution majority to the final Valence Band structure
was found as one of the sequences of intermediate transient mode. It was shown
that most of the qualified and discussed modes were accompanied by the MRO
(middle range ordering) distortions in the initial oxygen subnetwork of the
a-SiO2 host-matrix because of the appeared mixed defect configurations.Comment: 19 pages, 7 figures, accepted to J. Alloys and Compound
Orbital Period and Outburst Luminosity of Transient Low Mass X-ray Binaries
In this paper we investigate the relation between the maximal luminosity of
X-ray outburst and the orbital period in transient low mass X-ray binaries (or
soft X-ray transients) observed by the Rossi X-ray Timing Explorer (RXTE) in
the past decade. We find that the maximal luminosity (3-200 keV) in Eddington
unit generally increases with increasing orbital period, which does not show a
luminosity saturation but in general agrees with theoretical prediction. The
peak luminosities in ultra-compact binaries might be higher than those with
orbital period of 2-4 h, but more data are needed to make the claim. We also
find that there is no significant difference in the 3-200 keV outburst peak
luminosity between neutron star systems and black hole systems with orbital
periods above 4 h; however, there might be significant difference at smaller
orbital period where only neutron star systems are observed and radiatively
ineffcient accretion flow is expected to work at the low luminosities for black
hole accreters.Comment: 28 pages, 5 figures, accepted by Ap
An additional soft X-ray component in the dim low/hard state of black hole binaries
We test the truncated disc models using multiwavelength (optical/UV/X-ray)
data from the 2005 hard state outburst of the black hole SWIFT J1753.5-0127.
This system is both fairly bright and has fairly low interstellar absorption,
so gives one of the best datasets to study the weak, cool disc emission in this
state. We fit these data using models of an X-ray illuminated disc to constrain
the inner disc radius throughout the outburst. Close to the peak, the observed
soft X-ray component is consistent with being produced by the inner disc, with
its intrinsic emission enhanced in temperature and luminosity by reprocessing
of hard X-ray illumination in an overlap region between the disc and corona.
This disc emission provides the seed photons for Compton scattering to produce
the hard X-ray spectrum, and these hard X-rays also illuminate the outer disc,
producing the optical emission by reprocessing.
However, the situation is very different as the outburst declines. The
optical is probably cyclo-synchrotron radiation, self-generated by the flow,
rather than tracing the outer disc. Similarly, limits from reprocessing make it
unlikely that the soft X-rays are directly tracing the inner disc radius. This
is seen more clearly in a similarly dim low/hard state spectrum from XTE
J1118+480. The very small emitting area implied by the relatively high
temperature soft X-ray component is completely inconsistent with the much
larger, cooler, UV component which is well fit by a truncated disc. We
speculate on the origin of this component, but its existence as a clearly
separate spectral component from the truncated disc in XTE J1118+480 shows that
it does not simply trace the inner disc radius, so cannot constrain the
truncated disc models.Comment: 11 pages, 10 figures, submitted to MNRA
Black Hole and Neutron Star Transients in Quiescence
We consider the X-ray luminosity difference between neutron star and black
hole soft X-ray transients (NS and BH SXTs) in quiescence. The current
observational data suggest that BH SXTs are significantly fainter than NS SXTs.
The luminosities of quiescent BH SXTs are consistent with the predictions of
binary evolution models for the mass transfer rate if (1) accretion occurs via
an ADAF in these systems and (2) the accreting compact objects have event
horizons. The luminosities of quiescent NS SXTs are not consistent with the
predictions of ADAF models when combined with binary evolution models, unless
most of the mass accreted in the ADAF is prevented from reaching the neutron
star surface. We consider the possibility that mass accretion is reduced in
quiescent NS SXTs because of an efficient propeller and develop a model of the
propeller effect that accounts for the observed luminosities. We argue that
modest winds from ADAFs are consistent with the observations while strong winds
are probably not.Comment: LateX, 37 pages, 7 figures; Accepted for publication in The
Astrophysical Journa
Domain kinetics in [001] -poled PMN-39PT single crystal during polarization reversal
The equipment of the Ural Center for Shared Use “Modern Nanotechnology” Ural Federal University has been used. The research was made possible in part by Government of the Russian Federation (Act 211, Agreement 02.180 A03.21.0006) and RFBR (grant 17-52-80116-BRICS_a). V.S. and A.A. acknowledge financial support within the State Task from the Ministry of Education and Science of the Russian Federation (Project No. 1366.2014/236 and contract No. 3.4973.2017/7.8)
The 2009 outburst of H~1743-322 as observed by RXTE
We analyze the RXTE observations of the 2009 outburst of H~1743-322, as well
as the observations of the previous five outbursts for comparison. The
hardness-intensity diagram (HID) shows a complete counter-clockwise q-track for
the 2009 outburst and, interestingly, the track falls in} between a huge one in
2003, with a complete transition to high/soft state, and that of} the failed
outburst in 2008. It leaves the low/hard state but does not reach the leftmost
edge of the overall HID. While the lowest hardness (6--19 keV/3--6 keV) values}
in the HID is about 0.3--0.4 for the 2009 outburst, similar to the ``failed
state transition" seen in the persistent black hole XRB Cyg X-1, the timing
analysis shows that a transition to the high soft state occurred. During the
low/hard state of the 2009 outburst, the inner radius of the accretion disk is
found to be closer to the central black hole and have an anti-correlation with
the disk temperature. These results may be understood as the reprocessing} of
the hot corona on the disk's} soft X-rays, which can lead to an underestimation
of the inner radius of the accretion disk. In the luminosity diagram of the
corona versus the disk, the tracks of the outbursts} in 2003 and 2009 cross the
line which represents a roughly equal contribution to the entire emission from
the thermal and the non-thermal components;} the track of the 2008 outburst has
the turn-over falling} on this line. This may be indicative of an emission
balance between the corona and the disk, which prevents the state transition
from going further than the low/hard state.Comment: accepted by A&
Vertically Self-Gravitating ADAFs in the Presence of Toroidal Magnetic Field
Force due to the self-gravity of the disc in the vertical direction is
considered to study its possible effects on the structure of a magnetized
advection-dominated accretion disc. We present steady-sate self similar
solutions for the dynamical structure of such a type of the accretion flows.
Our solutions imply reduced thickness of the disc because of the self-gravity.
It also imply that the thickness of the disc will increase by adding the
magnetic field strength.Comment: Accepted for publication in Astrophysics and Space Science
The correlation timescale of the X-ray flux during the outbursts of soft X-ray transients
Recent studies of black hole and neutron star low mass X-ray binaries (LMXBs)
show a positive correlation between the X-ray flux at which the
low/hard(LH)-to-high/soft(HS) state transition occurs and the peak flux of the
following HS state. By analyzing the data from the All Sky Monitor (ASM)
onboard the Rossi X-ray Timing Explorer (RXTE), we show that the HS state flux
after the source reaches its HS flux peak still correlates with the transition
flux during soft X-ray transient (SXT) outbursts. By studying large outbursts
or flares of GX 339-4, Aql X-1 and 4U 1705-44, we have found that the
correlation holds up to 250, 40, and 50 d after the LH-to-HS state transition,
respectively. These time scales correspond to the viscous time scale in a
standard accretion disk around a stellar mass black hole or a neutron star at a
radius of ~104-5 Rg, indicating that the mass accretion rates in the accretion
flow either correlate over a large range of radii at a given time or correlate
over a long period of time at a given radius. If the accretion geometry is a
two-flow geometry composed of a sub-Keplerian inflow or outflow and a disk flow
in the LH state, the disk flow with a radius up to ~105 Rg would have
contributed to the nearly instantaneous non-thermal radiation directly or
indirectly, and therefore affects the time when the state transition occurs.Comment: 7 pages, 3 figure
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