74 research outputs found
Machine learning reveals orbital interaction in crystalline materials
We propose a novel representation of crystalline materials named
orbital-field matrix (OFM) based on the distribution of valence shell
electrons. We demonstrate that this new representation can be highly useful in
mining material data. Our experiment shows that the formation energies of
crystalline materials, the atomization energies of molecular materials, and the
local magnetic moments of the constituent atoms in transition metal--rare-earth
metal bimetal alloys can be predicted with high accuracy using the OFM.
Knowledge regarding the role of coordination numbers of transition-metal and
rare-earth metal elements in determining the local magnetic moment of
transition metal sites can be acquired directly from decision tree regression
analyses using the OFM.Comment: 10 page
Bayesian Approach to Find a Long-Term Trend in Erratic Polarization Variations Observed in Blazars
We developed a method to separate a long-term trend from observed temporal
variations of polarization in blazars using a Bayesian approach. The temporal
variation of the polarization vector is apparently erratic in most blazars,
while several objects occasionally exhibited systematic variations, for
example, an increase of the polarization degree associated with a flare of the
total flux. We assume that the observed polarization vector is a superposition
of distinct two components, a long-term trend and a short-term variation
component responsible for short flares. Our Bayesian model estimates the
long-term trend which satisfies the condition that the total flux correlates
with the polarized flux of the short-term component. We demonstrate that
assumed long-term polarization components are successfully separated by the
Bayesian model for artificial data. We applied this method to photopolarimetric
data of OJ 287, S5 0716+714, and S2 0109+224. Simple and systematic long-term
trends were obtained in OJ 287 and S2 0109+224, while no such a trend was
identified in S5 0716+714. We propose that the apparently erratic variations of
polarization in OJ 287 and S2 0109+224 are due to the presence of the long-term
polarization component. The behavior of polarization in S5 0716+714 during our
observation period implies the presence of a number of polarization components
having a quite short time-scale of variations.Comment: 12 pages, 7 figures, accepted for publication in PAS
Assessment of Myocardial Function During Mechanical Left Ventricular Support Using Serial Echocardiography: A Case Report
A 40-year-old man with valvular heart disease was successfully treated using a left ventricular assist device (LVAD) after open heart surgery. Echocardiography revealed left ventricular ejection fraction (LV-EF) at LVAD on/off: 23.4%/14.6% on the 4th, 23.8%/23.8% on the 5th, and 23.8%/26.8% on the 6th postoperative day (POD), respectively. The patient was weaned from LVAD on the 8th POD and discharged from the hospital on the 58th POD. The LV-EF improved to 54% 6 months after surgery and increased from 57% to 64% in response to exercise stress testing 1 year after surgery.</p
Photopolarimetric Monitoring of Blazars in the Optical and Near-Infrared Bands with the Kanata Telescope. I. Correlations between Flux, Color, and Polarization
We report on the correlation between the flux, color and polarization
variations on time scales of days--months in blazars, and discuss their
universal aspects. We performed monitoring of 42 blazars in the optical and
near-infrared bands from 2008 to 2010 using TRISPEC attached to the "Kanata"
1.5-m telescope. We found that 28 blazars exhibited "bluer-when-brighter"
trends in their whole or a part of time-series data sets. This corresponds to
88% of objects that were observed for >10 days. Thus, our observation
unambiguously confirmed that the "bluer-when-brighter" trend is common in the
emission from blazar jets. This trend was apparently generated by a variation
component with a constant and relatively blue color and an underlying red
component. Prominent short-term flares on time scales of days--weeks tended to
exhibit a spectral hysteresis; their rising phases were bluer than their decay
phases around the flare maxima. In contrast to the strong flux--color
correlation, the correlation of the flux and polarization degree was relatively
weak; only 10 objects showed significant positive correlations. Rotations of
polarization were detected only in three objects: PKS 1510-089, 3C 454.3, and
PKS 1749+096, and possibly in S5 0716+714. We also investigated the dependence
of the degree of variability on the luminosity and the synchrotron peak
frequency, \nu_peak. As a result, we found that lower luminosity and higher
\nu_peak objects had smaller variations in their amplitudes both in the flux,
color, and polarization degree. Our observation suggests the presence of
several distinct emitting sources, which have different variation time-scales,
colors, and polarizations. We propose that the energy injection by, for
example, internal shocks in relativistic shells is a major factor for blazar
variations on time scales of both days and months.Comment: 39 pages, accepted for publication in PAS
Detection of Polarimetric Variations Associated with the Shortest Time-Scale Variability in S5 0716714
We present the result of near-infrared and optical observations of the BL Lac
object S5 0716714 carried out by the KANATA telescope. S5 0716714 has
both a long term high-amplitude variability and a short-term variability within
a night. The shortest variability (microvariability) time-scale is important
for understanding the geometry of jets and magnetic field, because it provides
a possible minimum size of variation sources. Here, we report the detection of
15-min variability in S5 0716714, which is one of the shortest time-scales
in optical and near-infrared variations observed in blazars. The detected
microvariation had an amplitude of mag in band and a blue
color of . Furthermore, we successfully detected
an unprecedented, short time-scale polarimetric variation which correlated with
the brightness change. We revealed that the microvariation had a specific
polarization component. The polarization degree of the variation component was
higher than that of the total flux. These results suggest that the
microvariability originated from a small and local region where the magnetic
field is aligned.Comment: 5 pages, 4 figures; Publications of the Astronomical Society of Japan
letter accepte
Dwarf Novae in the Shortest Orbital Period Regime: I. A New Short Period Dwarf Nova, OT J055717+683226
We report the observation of a new dwarf nova, OT J055717+683226, during its
first-ever recorded superoutburst in December 2006. Our observation shows that
this object is an SU UMa-type dwarf nova having a very short superhump period
of 76.67+/- 0.03 min (0.05324+/-0.00002 d). The next superoutburst was observed
in March 2008. The recurrence time of superoutbursts (supercycle) is, hence,
estimated to be ~480 d. The supercycle is much shorter than those of WZ
Sge-type dwarf novae having supercycles of >~ 10 yr, which are a major
population of dwarf novae in the shortest orbital period regime (<~85 min).
Using a hierarchical cluster analysis, we identified seven groups of dwarf
novae in the shortest orbital period regime. We identified a small group of
objects that have short supercycles, small outburst amplitudes, and large
superhump period excesses, compared with those of WZ Sge stars. OT
J055717+683226 probably belongs to this group.Comment: 14 pages, 11 figures, accepted for publication in PAS
Optical and Near-Infrared Photometry of Nova V2362 Cyg : Rebrightening Event and Dust Formation
We present optical and near-infrared (NIR) photometry of a classical nova,
V2362 Cyg (= Nova Cygni 2006). V2362 Cyg experienced a peculiar rebrightening
with a long duration from 100 to 240 d after the maximum of the nova. Our
multicolor observation indicates an emergence of a pseudophotosphere with an
effective temperature of 9000 K at the rebrightening maximum. After the
rebrightening maximum, the object showed a slow fading homogeneously in all of
the used bands for one week. This implies that the fading just after the
rebrightening maximum ( less or equal 1 week ) was caused by a slowly shrinking
pseudophotosphere. Then, the NIR flux drastically increased, while the optical
flux steeply declined. The optical and NIR flux was consistent with blackbody
radiation with a temperature of 1500 K during this NIR rising phase. These
facts are likely to be explained by dust formation in the nova ejecta. Assuming
an optically thin case, we estimate the dust mass of 10^(-8) -- 10^(-10)
M_solar, which is less than those in typical dust-forming novae. These results
support the senario that a second, long-lasting outflow, which caused the
rebrightening, interacted with a fraction of the initial outflow and formed
dust grains.Comment: 6 pages, 4 figures, 2010, PASJ, 62, 1103--1108, in pres
Multi-Wavelength Photometric and Polarimetric Observations of the Outburst of 3C 454.3 in Dec. 2009
In December 2009, the bright blazar, 3C 454.3 exhibited a strong outburst in
the optical, X-ray and gamma-ray regions. We performed photometric and
polarimetric monitoring of this outburst in the optical and near-infrared bands
with TRISPEC and HOWPol attached to the Kanata telescope. We also observed this
outburst in the infrared band with AKARI, and the radio band with the 32-m
radio telescope of Yamaguchi University. The object was in an active state from
JD 2455055 to 2455159. It was 1.3 mag brighter than its quiescent state before
JD 2455055 in the optical band. After the end of the active state in JD
2455159, a prominent outburst was observed in all wavelengths. The outburst
continued for two months. Our optical and nearinfrared polarimetric
observations revealed that the position angle of the polarization (PA)
apparently rotated clockwise by 240 degrees within 11 d in the active state (JD
2455063-2455074), and after this rotation, PA remained almost constant during
our monitoring. In the outburst state, PA smoothly rotated counterclockwise by
350 degrees within 35 d (JD 2455157-2455192). Thus, we detected two distinct
rotation events of polarization vector in opposite directions. We discuss these
two events compared with the past rotation events observed in 2005, 2007 and
2008.Comment: 9 pages, 6 figures, accepted for publication in PAS
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