49,654 research outputs found
Flux rope proxies and fan-spine structures in active region NOAA 11897
Employing the high-resolution observations from the Solar Dynamics
Observatory (SDO) and the Interface Region Imaging Spectrograph (IRIS), we
statistically investigate flux rope proxies in NOAA AR 11897 from 14-Nov-2013
to 19-Nov-2013 and display two fan-spine structures in this AR. For the first
time, we detect flux rope proxies of NOAA 11897 for total 30 times in 4
different locations. These flux rope proxies were either tracked in both lower
and higher temperature wavelengths or only detected in hot channels. Specially,
none of these flux rope proxies was observed to erupt, but just faded away
gradually. In addition to these flux rope proxies, we firstly detect a
secondary fan-spine structure. It was covered by dome-shaped magnetic fields
which belong to a larger fan-spine topology. These new observations imply that
considerable amounts of flux ropes can exist in an AR and the complexity of AR
magnetic configuration is far beyond our imagination.Comment: 8 pages, 8 figures, Accepted for publication in A&
Heat conduction in 2D strongly-coupled dusty plasmas
We perform non-equilibrium simulations to study heat conduction in
two-dimensional strongly coupled dusty plasmas. Temperature gradients are
established by heating one part of the otherwise equilibrium system to a higher
temperature. Heat conductivity is measured directly from the stationary
temperature profile and heat flux. Particular attention is paid to the
influence of damping effect on the heat conduction. It is found that the heat
conductivity increases with the decrease of the damping rate, while its
magnitude agrees with previous experimental measurement.Comment: 4 pages, 2 figures, presented in SCCS2008 conferenc
Propagating wave in active region-loops, located over the solar disk observed by the Interface Region Imaging Spectrograph
We aim to ascertain the physical parameters of a propagating wave over the
solar disk detected by the Interface Region Imaging Spectrograph (IRIS). Using
imaging data from the IRIS and the Solar Dynamic Observatory (SDO), we tracked
bright spots to determine the parameters of a propagating transverse wave in
active region (AR) loops triggered by activation of a filament. Deriving the
Doppler velocity of Si IV line from spectral observations of IRIS, we have
determined the rotating directions of active region loops which are relevant to
the wave. On 2015 December 19, a filament was located on the polarity inversion
line of the NOAA AR 12470. The filament was activated and then caused a C 1.1
two-ribbon flare. Between the flare ribbons, two rotation motions of a set of
bright loops were observed to appear in turn with opposite directions.
Following the end of the second rotation, a propagating wave and an associated
transverse oscillation were detected in these bright loops. In 1400 A channel,
there was bright material flowing along the loops in a wave-like manner, with a
period of ~128 s and a mean amplitude of ~880 km. For the transverse
oscillation, we tracked a given loop and determine the transverse positions of
the tracking loop in a limited longitudinal range. In both of 1400 A and 171 A
channels, approximately four periods are distinguished during the transverse
oscillation. The mean period of the oscillation is estimated as ~143 s and the
displacement amplitude as between ~1370 km and ~690 km. We interpret these
oscillations as a propagating kink wave and obtain its speed of ~1400 km s-1.
Our observations reveal that a flare associated with filament activation could
trigger a kink propagating wave in active region loops over the solar disk.Comment: Accepted for publication in A&
The observed spiral structure of the Milky Way
The spiral structure of the Milky Way is not yet well determined. The keys to
understanding this structure are to increase the number of reliable spiral
tracers and to determine their distances as accurately as possible. HII
regions, giant molecular clouds (GMCs), and 6.7-GHz methanol masers are closely
related to high mass star formation, and hence they are excellent spiral
tracers. We update the catalogs of Galactic HII regions, GMCs, and 6.7-GHz
methanol masers, and then outline the spiral structure of the Milky Way. We
collected data for more than 2500 known HII regions, 1300 GMCs, and 900 6.7-GHz
methanol masers. If the photometric or trigonometric distance was not yet
available, we determined the kinematic distance using a Galaxy rotation curve
with the current IAU standard, = 8.5 kpc and = 220 km
s, and the most recent updated values of = 8.3 kpc and
= 239 km s, after we modified the velocities of tracers with the adopted
solar motions. With the weight factors based on the excitation parameters of
HII regions or the masses of GMCs, we get the distributions of these spiral
tracers. The distribution of tracers shows at least four segments of arms in
the first Galactic quadrant, and three segments in the fourth quadrant. The
Perseus Arm and the Local Arm are also delineated by many bright HII regions.
The arm segments traced by massive star forming regions and GMCs are able to
match the HI arms in the outer Galaxy. We found that the models of three-arm
and four-arm logarithmic spirals are able to connect most spiral tracers. A
model of polynomial-logarithmic spirals is also proposed, which not only
delineates the tracer distribution, but also matches the observed tangential
directions.Comment: 22 Pages, 16 Figures, 7 Tables, updated to match the published
versio
A q-Analog of Dual Sequences with Applications
In the present paper combinatorial identities involving q-dual sequences or
polynomials with coefficients q-dual sequences are derived. Further,
combinatorial identities for q-binomial coefficients(Gaussian coefficients),
q-Stirling numbers and q-Bernoulli numbers and polynomials are deduced.Comment: 14 page
Open clusters: their kinematics and metellicities
We review our work on Galactic open clusters in recent years, and introduce
our proposed large program for the LOCS (LAMOST Open Cluster Survey). First,
based on the most complete open clusters sample with metallicity, age and
distance data as well as kinematic information, some preliminary statistical
analysis regarding the spatial and metallicity distributions is presented. In
particular, a radial abundance gradient of - 0.058 0.006 dex kpc
was derived, and by dividing clusters into age groups we show that the disk
abundance gradient was steeper in the past. Secondly, proper motions,
membership probabilities, and velocity dispersions of stars in the regions of
two very young open clusters are derived. Both clusters show clear evidence of
mass segregation, which provides support for the ``primordial'' mass
segregation scenarios. Based on the great advantages of the forthcoming LAMOST
facility, we have proposed a detailed open cluster survey with LAMOST (the
LOCS). The aim, feasibility, and the present development of the LOCS are
briefly summarized.Comment: 7 pages, 4 figures, submitted to Proceeding of IAU Symposium No.248:
"A Giant Step:from Milli- to Micro-arcsecond Astrometry
On processing development for fabrication of fiber reinforced composite, part 2
Fiber-reinforced composite laminates are used in many aerospace and automobile applications. The magnitudes and durations of the cure temperature and the cure pressure applied during the curing process have significant consequences for the performance of the finished product. The objective of this study is to exploit the potential of applying the optimization technique to the cure cycle design. Using the compression molding of a filled polyester sheet molding compound (SMC) as an example, a unified Computer Aided Design (CAD) methodology, consisting of three uncoupled modules, (i.e., optimization, analysis and sensitivity calculations), is developed to systematically generate optimal cure cycle designs. Various optimization formulations for the cure cycle design are investigated. The uniformities in the distributions of the temperature and the degree with those resulting from conventional isothermal processing conditions with pre-warmed platens. Recommendations with regards to further research in the computerization of the cure cycle design are also addressed
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