1,690 research outputs found
Characteristics of Low-Latitude Coronal Holes near the Maximum of Solar cycle 24
We investigate the statistics of 288 low-latitude coronal holes extracted
from SDO/AIA-193 filtergrams over the time range 2011/01/01 to 2013/12/31. We
analyse the distribution of characteristic coronal hole properties, such as the
areas, mean AIA-193 intensities, and mean magnetic field densities, the local
distribution of the SDO/AIA-193 intensity and the magnetic field within the
coronal holes, and the distribution of magnetic flux tubes in coronal holes. We
find that the mean magnetic field density of all coronal holes under study is
3.0 +- 1.6 G, and the percentage of unbalanced magnetic flux is 49 +- 16 %. The
mean magnetic field density, the mean unsigned magnetic field density, and the
percentage of unbalanced magnetic flux of coronal holes depend strongly
pairwise on each other, with correlation coefficients cc > 0.92. Furthermore,
we find that the unbalanced magnetic flux of the coronal holes is predominantly
concentrated in magnetic flux tubes: 38 % (81 %) of the unbalanced magnetic
flux of coronal holes arises from only 1 % (10 %) of the coronal hole area,
clustered in magnetic flux tubes with field strengths > 50 G (10 G). The
average magnetic field density and the unbalanced magnetic flux derived from
the magnetic flux tubes correlate with the mean magnetic field density and the
unbalanced magnetic flux of the overall coronal hole (cc > 0.93). These
findings give evidence that the overall magnetic characteristics of coronal
holes are governed by the characteristics of the magnetic flux tubes.Comment: 15 figure
Outbursts from IGR J17473-2721
We have investigated the outbursts of IGR J17473-2721. We analyzed all
available observations carried out by RXTE on IGR J17473-2721 during its later
outburst and as well all the available SWIFT/BAT data. The flux of the latter
outburst rose in ~ one month and then kept roughly constant for the following ~
two months. During this time period, the source was in a low/hard state. The
source moved to a high/soft state within the following three days, accompanied
by the occurrence of an additional outburst at soft X-rays and the end of the
preceding outburst in hard X-rays. During the decay of this soft outburst, the
source went back to a low/hard state within 6 days, with a luminosity 4 times
lower than the first transition. This shows a full cycle of the hysteresis in
transition between the hard and the soft states. The fact that the flux
remained roughly constant for ~ two months at times prior to the spectral
transition to a high/soft state might be regarded as the result of balancing
the evaporation of the inner disk and the inward accretion flow, in a model in
which the state transition is determined by the mass flow rate. Such a balance
might be broken via an additional mass flow accreting onto the inner disk,
which lightens the extra soft outburst and causes the state transition.
However, the possibility of an origin of the emission from the jet during this
time period cannot be excluded. The spectral analysis suggests an inclined XRB
system for IGR J17473-2721. Such a long-lived preceding low/hard state makes
IGR J17473-2721 resemble the behavior of outbursts seen in black hole X-ray
binaries like GX 339-4.Comment: A&A in pres
Two-temperature coronal flow above a thin disk
We extended the disk corona model (Meyer & Meyer-Hofmeister 1994; Meyer, Liu,
& Meyer-Hofmeister 2000a) to the inner region of galactic nuclei by including
different temperatures in ions and electrons as well as Compton cooling. We
found that the mass evaporation rate and hence the fraction of accretion energy
released in the corona depend strongly on the rate of incoming mass flow from
outer edge of the disk, a larger rate leading to more Compton cooling, less
efficient evaporation and a weaker corona. We also found a strong dependence on
the viscosity, higher viscosity leading to an enhanced mass flow in the corona
and therefore more evaporation of gas from the disk below. If we take accretion
rates in units of the Eddington rate our results become independent on the mass
of the central black hole. The model predicts weaker contributions to the hard
X-rays for objects with higher accretion rate like narrow-line Seyfert 1
galaxies (NLS1s), in agreement with observations. For luminous active galactic
nuclei (AGN) strong Compton cooling in the innermost corona is so efficient
that a large amount of additional heating is required to maintain the corona
above the thin disk.Comment: 17 pages, 6 figures. ApJ accepte
Modelling the Recurrent Nova CI Aql in Quiescence
We present detailed photometric investigations of the recurrent nova CI Aql.
New data obtained after the 2000 outburst are used to derive a 3D geometrical
model of the system. The resulting light curves clearly indicate the existence
of an asymmetric spray around the accretion disk, as claimed in the past e.g.
for the super-soft X-ray source CAL87 in the LMC. The simulated light curves
give us the mass transfer rates varying from \dot M ~ 2.5 x 10^{-8} M_\odot /
yr in 1991-1996 to 5.5 x 10^{-8} < \dot M < 1.5 x 10^{-7}M_\odot / yr in
2001/2002. The distance and the interstellar foreground extinction resulting
from the model are 1.55 kpc and E(B-V) = 0.98 respectively. During fast
photometry sequences in 2002 short timescale variations (t ~ 13 minutes) of the
mass loss are found. Moreover a change in the orbital period of the system is
detectable and results in a mass loss of 2.2 x 10^{-6} < \Delta M < 5.7 x
10^{-6} M_\odot during the nova explosion.Comment: 9 pages 14 eps figures, to appear in Astron. & Astrophy
3-Phase Evolution of a Coronal Hole, Part I: 360{\deg} remote sensing and in-situ observations
We investigate the evolution of a well-observed, long-lived, low-latitude
coronal hole (CH) over 10 solar rotations in the year 2012. By combining EUV
imagery from STEREO-A/B and SDO we are able to track and study the entire
evolution of the CH having a continuous 360 coverage of the Sun. The
remote sensing data are investigated together with in-situ solar wind plasma
and magnetic field measurements from STEREO-A/B, ACE and WIND. From this we
obtain how different evolutionary states of the CH as observed in the solar
atmosphere (changes in EUV intensity and area) affect the properties of the
associated high-speed stream measured at AU. Most distinctly pronounced for
the CH area, three development phases are derived: a) growing, b) maximum, and
c) decaying phase. During these phases the CH area a) increases over a duration
of around three months from about to , b) keeps a rather constant area for about one month
of , and c) finally decreases in the
following three months below until the CH
cannot be identified anymore. The three phases manifest themselves also in the
EUV intensity and in in-situ measured solar wind proton bulk velocity.
Interestingly, the three phases are related to a different range in solar wind
speed variations and we find for the growing phase a range of
~km~s, for the maximum phase ~km~s, and for the
decaying phase a more irregular behavior connected to slow and fast solar wind
speed of ~km~s.Comment: Accepted for publication in Ap
A protocol for the induction of experimental necrotizing enterocolitis in neonatal mice
Recapitulating human NEC using animal models has been insightful in dissecting the signaling pathways, immune-mediated mechanisms, genetic signatures, and the intestinal architecture of NEC. This protocol describes a
A new clue to the transition mechanism between optical high and low states of the supersoft X-ray source RX J0513.9-6951, implied from the recurrent nova CI Aquilae 2000 outburst model
We have found a new clue to the transition mechanism between optical
high/X-ray off and optical low/X-ray on states of the LMC supersoft X-ray
source RX J0513.9-6951. A sharp ~1 mag drop is common to the CI Aql 2000
outburst. These drops are naturally attributed to cessation of optically thick
winds on white dwarfs. A detailed light-curve analysis of CI Aql indicates that
the size of a disk drastically shrinks when the wind stops. This causes ~1-2
mag drop in the optical light curve. In RX J0513.9-6951, the same mechanism
reproduces sharp ~1 mag drop from optical high to low states. We predict this
mechanism also works on the transition from low to high states. Interaction
between the wind and the companion star attenuates the mass transfer and drives
full cycles of low and high states.Comment: 9 pages including 5 figures, to appear in the Astrophysical Journa
The source ambiguity problem: Distinguishing the effects of grammar and processing on acceptability judgments
Judgments of linguistic unacceptability may theoretically arise from either grammatical deviance or significant processing difficulty. Acceptability data are thus naturally ambiguous in theories that explicitly distinguish formal and functional constraints. Here, we consider this source ambiguity problem in the context of Superiority effects: the dispreference for ordering a wh-phrase in front of a syntactically âsuperiorâ wh-phrase in multiple wh-questions, e.g., What did who buy? More specifically, we consider the acceptability contrast between such examples and so-called D-linked examples, e.g., Which toys did which parents buy? Evidence from acceptability and self-paced reading experiments demonstrates that (i) judgments and processing times for Superiority violations vary in parallel, as determined by the kind of wh-phrases they contain, (ii) judgments increase with exposure, while processing times decrease, (iii) reading times are highly predictive of acceptability judgments for the same items, and (iv) the effects of the complexity of the wh-phrases combine in both acceptability judgments and reading times. This evidence supports the conclusion that D-linking effects are likely reducible to independently motivated cognitive mechanisms whose effects emerge in a wide range of sentence contexts. This in turn suggests that Superiority effects, in general, may owe their character to differential processing difficulty
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