3,444 research outputs found
Solar Flares with an Exponential Growth of the Emission Measure in the Impulsive Phase Derived from X-ray Observations
The light curves of solar flares in the impulsive phase are complex in
general, indicating that multiple physical processes are involved in. With the
GOES (Geostationary Operational Environmental Satellite) observations, we find
that there are a subset of flares, whose impulsive phases are dominated by a
period of exponential growth of the emission measure. The flares occurred from
January 1999 to December 2002 are analyzed, and the results from the
observations made with both GOES 8 and GEOS 10 satellites are compared to
estimate the instrumental uncertainties. Their mean temperatures during this
exponential growth phase have a normal distribution. Most flares within the
1\sigma\ range of this temperature distribution belong to the GOES class B or
C, with the peak fluxes at the GOES low-energy channel following a log-normal
distribution. The growth rate and duration of the exponential growth phase also
follow a lognormal distribution, in which the duration is distributed in the
range from half a minute to about half an hour. As expected, the growth time is
correlated with the decay time of the soft X-ray flux. We also find that the
growth rate of the emission measure is strongly anti-correlated with the
duration of the exponential growth phase, and the mean temperature increases
slightly with the increase of the growth rate. The implications of these
results on the study of energy release in solar flares are discussed in the
end.Comment: 10 figure
Hamiltonian Structures and Reciprocal Transformations for the -KdV-CH Hierarchy
The -KdV-CH hierarchy is a generalization of the Korteweg-de Vries and
Camassa-Holm hierarchies parametrized by constants. In this paper we
clarify some properties of its multi-Hamiltonian structures, prove the
semisimplicity of the associated bihamiltonian structures and the formula for
their central invariants. By introducing a class of generalized Hamiltonian
structures, we give in a natural way the transformation formulae of the
Hamiltonian structures of the hierarchy under certain reciprocal
transformation, and prove the formulae at the level of its dispersionless
limit. We also consider relations of the associated bihamiltonian structures to
Frobenius manifolds.Comment: 37 page
Constructing new pseudoscalar meson nonets with the observed , , and
Stimulated by the BESIII observation of , , and
, we try to pin down new pseudoscalar meson nonets including these
states. The analysis of mass spectra and the study of strong decays indicate
that and associated with and the predicted
kaon may form a new pseudoscalar meson nonet. In addition, more
experimental data for are necessary to determine its structure of
nonets. Then, , , , and the predicted kaon
can be grouped into another new nonet. These assignments to the
discussed pseudoscalar states can be further tested in experiment.Comment: 15 pages, 4 tables and 10 figures. More discussions added and typos
corrected. Accepted by Phys. Rev.
A GeV source in the direction of Supernova Remnant CTB 37B
Supernova remnants (SNRs) are the most attractive candidates for the
acceleration sites of Galactic cosmic rays. We report the detection of GeV
-ray emission with the Pass 8 events recorded by Fermi Large Area
Telescope (Fermi-LAT) in the vicinity of the shell type SNR CTB 37B that is
likely associated with the TeV ray source HESS J1713-381. The photon
spectrum of CTB 37B is consistent with a power-law with an index of
in the energy range of GeV, and the measured flux
connects smoothly with that of HESS J1713-381 at a few hundred GeV. No
significant spatial extension and time variation are detected. The
multi-wavelength data can be well fitted with either a leptonic model or a
hadronic one. However, parameters of both models suggest more efficient
particle acceleration than typical SNRs. Meanwhile, the X-ray and -ray
spectral properties of CTB 37B show that it is an interesting source bridging
young SNRs dominated by non-thermal emission and old SNRs interacting with
molecular clouds.Comment: 6 pages, 5 figures, 2 tables, published in ApJ, 817, 6
The SNR Puppis A Revisited with Seven Years of Fermi Large Area Telescope Observations
Puppis A is a very famous and extensively studied supernova remnant (SNR)
that shows strong evidence of shock-cloud interaction. We re-analyze the GeV
-ray emission of it using seven years Pass 8 data recorded by the Fermi
Large Area Telescope (Fermi-LAT). The morphology of the -ray emission
is more compatible with that of the thermal X-ray and IR emissions than the
radio image, which suggests a possible correlation between the gamma-ray
emitting region and dense clouds. The -ray spectrum in the energy range
of 1-500 GeV shows a break at GeV with the photon indices of
below the break and above the break, which can
naturally explain the lack of TeV -ray emission from Puppis A. The
multi-wavelength observations favor a hadronic origin for the -ray
emission.Comment: 9 pages, 4 figures, 4 tables, Accepted for publication in Ap
Studying hadronic decays and predicting its pion and kaon induced productions
The newly observed by the BESIII Collaboration inspires our
interest in studying the light meson system, especially axial-vector mesons.
Since the has possibilities but cannot be distinguished
only by mass, we make use of flux-tube model to study the strong decay behavior
of under this assignment. The experimental width of the newly
reported can be reproduced in our calculation, which favors an
assignment of as the second radial excitation of with
. And the has a
sizable contribution to the total width. Furthermore, we focus on the
production of and its flavour partner induced by pion and
kaon on a proton target with the Feynman model and the Regge model, which is an
available platform to further identify their nature. The numerical results
indicate that the total cross section are similar in the two models. When the
range of momentum is 10 to 30 GeV/, the total cross
sections for and are predicted to
be at an order of magnitude of 0.1 b. Whereas, the total cross section for
is near an order of magnitude of 10 b when
is from 10 to 30 GeV/, and much larger than that of
reaction . These predictions can provide some
valuable information to search for and in experiments at
J-PARC, COMPASS, OKA@U-70 and [email protected]: 9 pages and 8 figures. Accepted by Phys. Rev. D for publicatio
Almost ideal nodal-loop semimetal in monoclinic CuTeO material
Nodal-loop semimetals are materials in which the conduction and valence bands
cross on a one-dimensional loop in the reciprocal space. For the nodal-loop
character to manifest in physical properties, it is desired that the loop is
close to the Fermi level, relatively flat in energy, simple in its shape, and
not coexisting with other extraneous bands. Here, based on the first-principles
calculations, we show that the monoclinic CuTeO is a realistic nodal-loop
semimetal that satisfies all these requirements. The material features only a
single nodal loop around the Fermi level, protected by either of the two
independent symmetries: the symmetry and the glide mirror
symmetry. The size of the loop can be effectively tuned by strain, and the loop
can even be annihilated under stain, making a topological phase transition to a
trivial insulator phase. Including the spin-orbit coupling opens a tiny gap at
the loop, and the system becomes a topological semimetal with a
nontrivial bulk invariant but no global bandgap. The
corresponding topological surface states have been identified. We also
construct a low-energy effective model to describe the nodal loop and the
effect of spin-orbit coupling.Comment: 8 pages, 10 figure
General monogamy property of global quantum discord and the application
We provide a family of general monogamy inequalities for global quantum
discord (GQD), which can be considered as an extension of the usual discord
monogamy inequality. It can be shown that those inequalities are satisfied
under the similar condition for the holding of usual monogamy relation. We find
that there is an intrinsic connection among them. Furthermore, we present a
different type of monogamy inequality and prove that it holds under the
condition that the bipartite GQDs do not increase when tracing out some
subsystems. We also study the residual GQD based on the second type of monogamy
inequality. As applications of those quantities, we investigate the GQDs and
residual GQD in characterizing the quantum phase transition in the transverse
field Ising model.Comment: 11 pages, 6 figure
Statistical properties of radio flux densities of solar flares
Short timescale flux variations are closely related to the energy release
process of magnetic reconnection during solar flares. Radio light curves at 1,
2, 3.75, 9.4, and 17 GHz of 209 flares observed by the Nobeyama Radio
Polarimeter from 2000 to 2010 are analyzed with a running smooth technique. We
find that the impulsive component (with a variation timescale shorter than 1
second) of 1 GHz emission of most flares peaks at a few tens of solar flux unit
and lasts for about 1 minute and the impulsive component of 2 GHz emission
lasts a shorter period and peaks at a lower flux level, while at the three high
frequency channels the occurrence frequency of flares increases with the
decrease of the flux density up to the noise level of the corresponding
background. The gradual components of these emissions, however, have similar
duration and peak flux density distributions. We also derive the power spectrum
on different timescales and a normalized wavelet analysis is used to confirm
features on short timescales. At a time resolution of 0.1 second, more than
60 of these radio light curves show significant flux variation on 1
second or shorter time scales. This fraction increases with the decrease of
frequency and reaches 100 at 1 GHz, implying that short timescale
processes are universal in solar flares. We also study the correlation between
the impulsive radio flux densities and soft X-ray fluxes obtained with the GOES
satellites and find that more than 65 of the flares with an impulsive
component have their impulsive radio emission reach a peak value ahead of the
soft X-ray fluxes and this fraction increases with the radio frequency
Detecting degeneracy and subtle broken-symmetry states of graphene at nanoscale
Measuring degeneracy and broken-symmetry states of a system at nanoscale
requires extremely high energy and spatial resolution, which has so far eluded
direct observation. Here, we realize measurement of the degeneracy and subtle
broken-symmetry states of graphene at nanoscale for the first time. By using
edge-free graphene quantum dots, we are able to measure valley splitting and
valley-contrasting spin splitting of graphene at the single-electron level. Our
experiments detect large valley splitting around atomic defects of graphene due
to the coexistence of sublattice symmetry breaking and time reversal symmetry
breaking. Large valley-contrasting spin splitting induced by enhanced
spin-orbit coupling around the defects is also observed. These results reveal
unexplored exotic electronic states in graphene at nanoscale induced by the
atomic defects.Comment: 4 figures in main tex
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