211 research outputs found
Evolution of Synchrotron X-rays in Supernova Remnants
A systematic study of the synchrotron X-ray emission from supernova remnants
(SNRs) has been conducted. We selected a total of 12 SNRs whose synchrotron
X-ray spectral parameters are available in the literature with reasonable
accuracy, and studied how their luminosities change as a function of radius. It
is found that the synchrotron X-ray luminosity tends to drop especially when
the SNRs become larger than ~5 pc, despite large scatter. This may be explained
by the change of spectral shape caused by the decrease of the synchrotron
roll-off energy. A simple evolutionary model of the X-ray luminosity is
proposed and is found to reproduce the observed data approximately, with
reasonable model parameters. According to the model, the total energy of
accelerated electrons is estimated to be 10^(47-48) ergs, which is well below
the supernova explosion energy. The maximum energies of accelerated electrons
and protons are also discussed.Comment: 6 pages, 2 figures, ApJ, in pres
The Suzaku Observations of SS Cygni in Quiescence and Outburst
We present results from the Suzaku observations of the dwarf nova SS Cyg in
quiescence and outburst in 2005 November. Owing to high sensitivity of the HXD
PIN detector and high spectral resolution of the XIS, we have determined
parameters of the plasma with unprecedented precision. The maximum temperature
of the plasma in quiescence 20.4 +4.0-2.6 (stat.) +/- 3.0 (sys.) keV is
significantly higher than that in outburst 6.0 +0.2-1.3 keV. The elemental
abundances are close to the solar ones for the medium-Z elements (Si, S, Ar)
whereas they decline both in lighter and heavier elements. Those of oxygen and
iron are 0.46 and 0.37 solar, respectively. That of carbon is exceptionally
high and 2 solar at least. The solid angle of the reflector subtending over the
optically thin thermal plasma is Omega/2\pi = 1.7+/-0.2 (stat.) +/-0.1 (sys.)
in quiescence. A 6.4 keV iron Ka line is resolved into a narrow and broad
components. These facts indicate that both the white dwarf and the accretion
disk contribute to the continuum reflection and the 6.4 keV iron Ka line. We
consider the standard optically thin boundary layer as the most plausible
picture for the plasma configuration in quiescence. The solid angle of the
reflector in outburst Omega/2\pi = 0.9 +0.5-0.4 and a broad 6.4 keV iron line
indicates that the reflection in outburst originates from the accretion disk
and an equatorial accretion belt. From the energy width of the 6.4 keV line, we
consider the optically thin thermal plasma in outburst as being distributed on
the accretion disk like solar coronae.Comment: 28 pages, 15 figures, accepted for publication in PASJ Suzaku 3rd
special issue Pdf of this paper can be downloaded from
http://www.astro.isas.jaxa.jp/~ishida/Papers/sscyg_sub2.pd
Vulnerabilities of radiomic features to respiratory motion on four‐dimensional computed tomography‐based average intensity projection images: A phantom study
[Purpose] To evaluate the influence of respiratory motion on the robustness of radiomic features on four-dimensional computed tomography (4DCT)-based average intensity projection (AIP) images by employing an anthropomorphic chest phantom. [Methods] Three spherical objects (φ30 mm), namely, acrylic (100 Hounsfield unit [HU], homogeneous), rubber (−140 HU, homogeneous), and cork (−630 HU, heterogeneous), were moved with motion amplitudes of 0, 1, 2.5, 4, 6, 8, and 10 mm in the phantom, and 4DCT scans were repeated at four different locations. Thereafter, the AIP images were generated considering the average of the 10 respiratory phases of the 4DCT images. Further, the targets were manually delineated on the AIP images in the lung window setting. A total of 851 radiomic features, including 107 unfiltered features and 744 wavelet filter-based features, were extracted from the region of interest for each material. The feature robustness among the different target motion amplitude (ε) was evaluated by normalizing the feature variability of the target motion relative to the variability of data from 573 patients with early-stage non-small cell lung cancer. The features with absolute ε values ≤0.5 were considered highly robust to target motions. [Results] The percentage of robust unfiltered and wavelet filter-based features with a motion amplitude of 1 mm was greater than 83.2% and 93.4%, respectively; however, the percentage decreased by more than 24.3% and 17.6%, respectively, for motion amplitudes greater than 2.5 mm. The movement of cork had a small effect on the feature robustness compared to that of acrylic and rubber, regardless of the target motion amplitudes. [Conclusions] Our phantom study demonstrated that target motion amplitudes ≤1 mm led to the robustness of radiomic features on the 4DCT-based AIP images of thoracic regions. The frequency components and directions of the wavelet filters may be essential factors in 4DCT-based radiomic analysis
Suzaku Discovery of Hard X-ray Pulsations from the Rotating Magnetized White Dwarf, AE Aquarii
The fast rotating magnetized white dwarf, AE Aquarii, was observed with
Suzaku, in October 2005 and October 2006 with exposures of 53.1 and 42.4 ks,
respectively. In addition to clear spin modulation in the 0.5--10 keV band of
the XIS data at the barycentric period of 33.0769 \pm 0.0001 s, the 10--30 keV
HXD data in the second half of the 2005 observation also showed statistically
significant periodic signals at a consistent period. On that occasion, the
spin-folded HXD light curve exhibited two sharp spikes separated by about 0.2
cycles in phase, in contrast to approximately sinusoidal profiles observed in
energies below about 4 keV. The folded 4--10 keV XIS light curves are
understood as a superposition of those two types of pulse profiles. The phase
averaged 1.5--10 keV spectra can be reproduced by two thermal components with
temperatures of keV and keV, but
the 12-25 keV HXD data show a significant excess above the extrapolated model.
This excess can be explained by either a power-law model with photon index of
or a third thermal component with a temperature of
keV. At a distance of 102 pc, the 4--30 keV luminosities of
the thermal and the additional components become and
erg s, respectively. The latter
corresponds to 0.09% of the spin down energy of the object. Possible emission
mechanisms of the hard pulsations are discussed, including in particular
non-thermal ones.Comment: Accepted for publication on PASJ Vol.60, No.2, 2008 see Press Release
page(http://www.heal.phy.saitama-u.ac.jp/~terada/01work/press_release2008/index_e.html
Effect of CYP3A5*3 genetic variant on the metabolism of direct-acting antivirals in vitro : a different effect on asunaprevir versus daclatasvir and beclabuvir
Direct-acting antivirals, asunaprevir (ASV), daclatasvir (DCV), and beclabuvir (BCV) are known to be mainly metabolized by CYP3A enzymes; however, the differences in the detailed metabolic activities of CYP3A4 and CYP3A5 on these drugs are not well clarified. The aim of the present study was to elucidate the relative contributions of CYP3A4 and CYP3A5 to the metabolism of ASV, DCV, and BCV, as well as the effect of CYP3A5*3 genetic variant in vitro. The amount of each drug and their major metabolites were determined using LC-MS/MS. Recombinant CYP3As and CYP3A5*3-genotyped human liver microsomes (CYP3A5 expressers or non-expressers) were used for the determination of their metabolic activities. The contribution of CYP3A5 to ASV metabolism was considerable compared to that of CYP3A4. Consistently, ASV metabolic activity in CYP3A5 expressers was higher than those in CYP3A5 non-expresser. Moreover, CYP3A5 expression level was significantly correlated with ASV metabolism. In contrast, these observations were not found in DCV and BCV metabolism. To our knowledge, this is the first study to directly demonstrate the effect of CYP3A5*3 genetic variants on the metabolism of ASV. The findings of the present study may provide basic information on ASV, DCV, and BCV metabolisms
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