3,743 research outputs found
The least eigenvalue of graphs whose complements are unicyclic
A graph in a certain graph class is called minimizing if the least eigenvalue
of the adjacency matrix of the graph attains the minimum among all graphs in
that class. Bell {\it et al.} have characterized the minimizing graphs in the
class of connected graphs of order and size , whose complements are
either disconnected or contain a clique of order at least . In this paper
we discuss the minimizing graphs of a special class of graphs of order
whose complements are connected and contains exactly one cycle (namely the the
class of graphs whose complements are unicyclic), and
characterize the unique minimizing graph in when
Shape transition with temperature of the pear-shaped nuclei in covariant density functional theory
The shape evolutions of the pear-shaped nuclei Ra and even-even
Ba with temperature are investigated by the finite-temperature
relativistic mean field theory with the treatment of pairing correlations by
the BCS approach. The free energy surfaces as well as the bulk properties
including deformations, pairing gaps, excitation energy, and specific heat for
the global minimum are studied. For Ra, three discontinuities found in
the specific heat curve indicate the pairing transition at temperature 0.4 MeV,
and two shape transitions at temperatures 0.9 and 1.0 MeV, namely one from
quadrupole-octupole deformed to quadrupole deformed, and the other from
quadrupole deformed to spherical. Furthermore, the gaps at 136 and 88
are responsible for stabilizing the octupole-deformed global minimum at low
temperatures. Similar pairing transition at 0.5 MeV and shape
transitions at =0.5-2.2 MeV are found for even-even Ba. The
transition temperatures are roughly proportional to the corresponding
deformations at the ground states.Comment: 19 pages, 11 figure
Coexistence curve and molecule number density of AdS topological charged black hole in massive gravity
The coexistence curve and molecule number density of a 4-dimensional AdS
topological charged black hole in massive gravity is investigated. We find that
the analytic expression of the coexistence curve in the reduced parameter space
is dependent on theory parameters. This is very different from the previous
results obtained in other modified gravity such as gravity and
Gauss-Bonnet gravity. Besides, we derive the explicit expression of the
physical quantity which describes the difference of the number densities of AdS
topological charged black hole molecules between the small and large black
hole. It is observed that the difference of the molecule number densities is
also dependent on theory parameters. Both the expressions of the coexistence
curve and the difference of the molecule number densities can be reduced into a
form which is similar to a RN-AdS black hole if the mass of graviton is
zero. Moreover, we find the shifted temperature under massive gravity. This can
highlight the important role played by the mass of graviton and other
parameters in the phase transitions of AdS black holes in massive gravity.Comment: 11 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1604.07931, arXiv:1506.03578 by other author
Coupled Self-Organized Hydrodynamics and Navier-Stokes models: local well-posedness and the limit from the Self-Organized Kinetic-fluid models
A coupled system of self-organized hydrodynamics and Navier-Stokes equations
(SOH-NS), which models self-propelled particles in a viscous fluid, was
recently derived by Degond et al. \cite{DMVY-2017-arXiv}, starting from a
micro-macro particle system of Vicsek-Navier-Stokes model, through an
intermediate step of a self-organized kinetic-kinetic model by multiple
coarse-graining processes. We first transfer SOH-NS into a non-singular system
by stereographic projection, then prove the local in time well-posedness of
classical solutions by energy method. Furthermore, employing the Hilbert
expansion approach, we justify the hydrodynamic limit from the self-organized
kinetic-fluid model to macroscopic dynamics. This provides the first
analytically rigorous justification of the modeling and asymptotic analysis in
\cite{DMVY-2017-arXiv}.Comment: 42 pages. arXiv admin note: text overlap with arXiv:1706.05666 by
other author
Constraint on the velocity dependent dark matter annihilation cross section from gamma-ray and kinematic observations of ultrafaint dwarf galaxies
Searching for gamma rays from dwarf spheroidal galaxies (dSphs) is a
promising approach to detect dark matter (DM) due to the high DM densities and
low baryon components in dSphs. The Fermi-LAT observations from dSphs have set
stringent constraints on the velocity independent annihilation cross section.
However, the constraints from dSphs may change in velocity dependent
annihilation scenarios because of the different velocity dispersions in
galaxies. In this work, we study how to set constraints on the velocity
dependent annihilation cross section from the combined Fermi-LAT observations
of dSphs with the kinematic data. In order to calculate the gamma ray flux from
the dSph, the correlation between the DM density profile and velocity
dispersion at each position should be taken into account. We study such
correlation and the relevant uncertainty from kinematic observations by
performing a Jeans analysis. Using the observational results of three
ultrafaint dSphs with large J-factors, including Willman 1, Reticulum II, and
Triangulum II, we set constraints on the p-wave annihilation cross section in
the Galaxy as an example.Comment: 10 pages, 13 figure
Scene Text Recognition with Sliding Convolutional Character Models
Scene text recognition has attracted great interests from the computer vision
and pattern recognition community in recent years. State-of-the-art methods use
concolutional neural networks (CNNs), recurrent neural networks with long
short-term memory (RNN-LSTM) or the combination of them. In this paper, we
investigate the intrinsic characteristics of text recognition, and inspired by
human cognition mechanisms in reading texts, we propose a scene text
recognition method with character models on convolutional feature map. The
method simultaneously detects and recognizes characters by sliding the text
line image with character models, which are learned end-to-end on text line
images labeled with text transcripts. The character classifier outputs on the
sliding windows are normalized and decoded with Connectionist Temporal
Classification (CTC) based algorithm. Compared to previous methods, our method
has a number of appealing properties: (1) It avoids the difficulty of character
segmentation which hinders the performance of segmentation-based recognition
methods; (2) The model can be trained simply and efficiently because it avoids
gradient vanishing/exploding in training RNN-LSTM based models; (3) It bases on
character models trained free of lexicon, and can recognize unknown words. (4)
The recognition process is highly parallel and enables fast recognition. Our
experiments on several challenging English and Chinese benchmarks, including
the IIIT-5K, SVT, ICDAR03/13 and TRW15 datasets, demonstrate that the proposed
method yields superior or comparable performance to state-of-the-art methods
while the model size is relatively small.Comment: 10 pages,4 figure
An X-ray periodicity of 1.8 hours in a narrow-line Seyfert 1 galaxy Mrk 766
In the narrow-line Seyfert 1 galaxy Mrk 766, a Quasi-Periodic Oscillation
(QPO) signal with a period of s is detected in the \emph{XMM-Newton}
data collected on 2005 May 31. This QPO signal is highly statistical
significant at the confidence level at with the quality factor of
. The X-ray intensity changed by a factor of 3 with root
mean square fractional variability of . Furthermore, this QPO signal
presents in the data of all three EPIC detectors and two RGS cameras and its
frequency follows the - relation spanning from
stellar-mass to supermassive black holes. Interestingly, a possible QPO signal
with a period of s had been reported in the literature. The
frequency ratio of these two QPO signals is 3:2. Our result is also in
support of the hypothesis that the QPO signals can be just transient. The
spectral analysis reveals that the contribution of the soft excess component
below 1 keV is different between epochs with and without QPO, this
property as well as the former frequency-ratio are well detected in X-ray BH
binaries, which may have shed some lights on the physical origin of our event.Comment: 7 pages, 5 figures, 1 table. Accepted for publication in Ap
Zitterbewegung effect in spin-orbit coupled spin-1 ultracold atoms
The Zitterbewegung effect in spin-orbit coupled spin-1 cold atoms is
investigated in the presence of the Zeeman field and a harmonic trap. It is
shown that the Zeeman field and the harmonic trap have significant effect on
the Zitterbewegung oscillatory behaviors. The external Zeeman field could
suppress or enhance the Zitterbewegung amplitude and change the frequencies of
oscillation. A much slowly damping Zitterbewegung oscillation can be achieved
by adjusting both the linear and quadratic Zeeman field. Multi-frequency
Zitterbewegung oscillation can be induced by the applied Zeeman field. In the
presence of the harmonic trap, the subpackets corresponding to different
eigenenergies would always keep coherent, resulting in the persistent
Zitterbewegung oscillations. The Zitterbewegung oscillation would display very
complicated and irregular oscillation characteristics due to the coexistence of
different frequencies of the Zitterbewegung oscillation. Numerical results show
that, the Zitterbewegung effect is robust even in the presence of interaction
between atoms.Comment: 9 pages, 8 figure
Charm quarks in medium and their contribution to di-electron spectra in relativistic heavy ion collisions
We study the dynamics of charm quarks in the partonic medium and its
implication to the di-electron spectra in high energy heavy ion collisions. The
charm quarks traversing a thermal medium is simulated by the relativistic
Langevin equation for elastic scatterings of charm quarks by thermal partons in
an expanding fireball. The transport coefficients of charm quarks are
calculated by the in-medium T-matrix method, where a static heavy quark
potential is used with parameters fitted by the lattice QCD results. The
di-electron invariant mass spectra are computed in most central collisions and
are compared to the STAR data. The angular correlations of di-electrons are
almost the same in and Au+Au collisions in the mass range
with the back-to-back feature. This means that the
angular correlation is intact even with medium interaction at the RHIC energy.Comment: Revtex 4, 10 pages, 7 figures. Accepted version to PR
SCAN: Sliding Convolutional Attention Network for Scene Text Recognition
Scene text recognition has drawn great attentions in the community of
computer vision and artificial intelligence due to its challenges and wide
applications. State-of-the-art recurrent neural networks (RNN) based models map
an input sequence to a variable length output sequence, but are usually applied
in a black box manner and lack of transparency for further improvement, and the
maintaining of the entire past hidden states prevents parallel computation in a
sequence. In this paper, we investigate the intrinsic characteristics of text
recognition, and inspired by human cognition mechanisms in reading texts, we
propose a scene text recognition method with sliding convolutional attention
network (SCAN). Similar to the eye movement during reading, the process of SCAN
can be viewed as an alternation between saccades and visual fixations. Compared
to the previous recurrent models, computations over all elements of SCAN can be
fully parallelized during training. Experimental results on several challenging
benchmarks, including the IIIT5k, SVT and ICDAR 2003/2013 datasets, demonstrate
the superiority of SCAN over state-of-the-art methods in terms of both the
model interpretability and performance
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