42,949 research outputs found
Group percolation in interdependent networks
In many real network systems, nodes usually cooperate with each other and
form groups, in order to enhance their robustness to risks. This motivates us
to study a new type of percolation, group percolation, in interdependent
networks under attacks. In this model, nodes belonging to the same group
survive or fail together. We develop a theoretical framework for this novel
group percolation and find that the formation of groups can improve the
resilience of interdependent networks significantly. However, the percolation
transition is always of first order, regardless of the distribution of group
sizes. As an application, we map the interdependent networks with
inter-similarity structures, which attract many attentions very recently, onto
the group percolation and confirm the non-existence of continuous phase
transitions
Superconducting energy gap versus pseudogap in hole-doped cuprates as revealed by infrared spectroscopy
We present in-plane infrared reflectance measurement on two superconducting
cuprates with relatively low T: a nearly optimally-doped
BiSrLaCuO with T=33 K and an underdoped
LaSrCuO with T=30 K. The measurement clearly reveals
that the superconducting energy gap is distinct from the pseudogap. They have
different energy scales and appear at different temperatures. The results
suggest that the pseudogap is not a precursor to the superconducting state. The
data also challenge the longstanding viewpoint that the superconductivity
within the ab-plane is in the clean limit and the superconducting pairing
energy gap could not be detected by in-plane infrared spectroscopy.Comment: 5 pages, 4 figure
Is the X-ray pulsating companion of HD 49798 a possible type Ia supernova progenitor?
HD 49798 (a hydrogen depleted subdwarf O6 star) with its massive white dwarf
(WD) companion has been suggested to be a progenitor candidate of type Ia
supernovae (SNe Ia). However, it is still uncertain whether the companion of HD
49798 is a carbon-oxygen (CO) WD or an oxygen-neon (ONe) WD. A CO WD will
explode as an SN Ia when its mass grows approach to Chandrasekhar mass, while
the outcome of an accreting ONe WD is likely to be a neutron star. We followed
a series of Monte Carlo binary population synthesis approach to simulate the
formation of ONe WD + He star systems. We found that there is almost no orbital
period as large as HD 49798 with its WD companion in these ONe WD + He star
systems based on our simulations, which means that the companion of HD 49798
might not be an ONe WD. We suggest that the companion of HD 49798 is most
likely a CO WD, which can be expected to increase its mass to the Chandrasekhar
mass limit by accreting He-rich material from HD 49798. Thus, HD 49798 with its
companion may produce an SN Ia in its future evolution.Comment: 9 pages, 3 figure
Quasi-Hamiltonian Method for Computation of Decoherence Rates
For many implementations of quantum computing, 1/f and other types of
broad-spectrum noise are an important source of decoherence. An important step
forward would be the ability to back out the characteristics of this noise from
qubit measurements and to see if it leads to new physical effects. For certain
types of qubits, the working point of the qubit can be varied. Using a new
mathematical method that is suited to treat all working points, we present
theoretical results that show how this degree of freedom can be used to extract
noise parameters and to predict a new effect: noise-induced looping on the
Bloch sphere. We analyze data on superconducting qubits to show that they are
very near the parameter regime where this looping should be observed.Comment: 15 pages, 4 figure
SE2Net: Siamese Edge-Enhancement Network for Salient Object Detection
Deep convolutional neural network significantly boosted the capability of
salient object detection in handling large variations of scenes and object
appearances. However, convolution operations seek to generate strong responses
on individual pixels, while lack the ability to maintain the spatial structure
of objects. Moreover, the down-sampling operations, such as pooling and
striding, lose spatial details of the salient objects. In this paper, we
propose a simple yet effective Siamese Edge-Enhancement Network (SE2Net) to
preserve the edge structure for salient object detection. Specifically, a novel
multi-stage siamese network is built to aggregate the low-level and high-level
features, and parallelly estimate the salient maps of edges and regions. As a
result, the predicted regions become more accurate by enhancing the responses
at edges, and the predicted edges become more semantic by suppressing the false
positives in background. After the refined salient maps of edges and regions
are produced by the SE2Net, an edge-guided inference algorithm is designed to
further improve the resulting salient masks along the predicted edges.
Extensive experiments on several benchmark datasets have been conducted, which
show that our method is superior than the state-of-the-art approaches
Frame-wise Motion and Appearance for Real-time Multiple Object Tracking
The main challenge of Multiple Object Tracking (MOT) is the efficiency in
associating indefinite number of objects between video frames. Standard motion
estimators used in tracking, e.g., Long Short Term Memory (LSTM), only deal
with single object, while Re-IDentification (Re-ID) based approaches
exhaustively compare object appearances. Both approaches are computationally
costly when they are scaled to a large number of objects, making it very
difficult for real-time MOT. To address these problems, we propose a highly
efficient Deep Neural Network (DNN) that simultaneously models association
among indefinite number of objects. The inference computation of the DNN does
not increase with the number of objects. Our approach, Frame-wise Motion and
Appearance (FMA), computes the Frame-wise Motion Fields (FMF) between two
frames, which leads to very fast and reliable matching among a large number of
object bounding boxes. As auxiliary information is used to fix uncertain
matches, Frame-wise Appearance Features (FAF) are learned in parallel with
FMFs. Extensive experiments on the MOT17 benchmark show that our method
achieved real-time MOT with competitive results as the state-of-the-art
approaches.Comment: 13 pages, 4 figures, 4 table
Testing reanalysis datasets in Antarctica: Trends, persistence properties and trend significance
The reanalysis datasets provide very important sources for investigating the
climate dynamics and climate changes in Antarctica. In this paper, three major
reanalysis data are compared with Antarctic station data over the last 35
years: the National Centers for Environmental Prediction and the National
Center for Atmospheric Research reanalysis (NCEP1), NCEP-DOE Reanalysis 2
(NCEP2), and the European Centre for Medium-Range Weather Forecasts Interim
Re-Analysis (ERA-Interim). In our assessment, we compare the linear trends, the
fluctuations around the trends, the persistence properties and the significance
level of warming trends in the reanalysis data with the observational ones. We
find that NCEP1 and NCEP2 show spurious warming trends in all parts of
Antarctica except the Peninsula, while ERA-Interim is quite reliable except at
Amundsen-Scott. To investigate the persistence of the data sets, we consider
the lag-1 autocorrelation and the Hurst exponent. While varies
quite erratically in different stations, the Hurst exponent shows similar
patterns all over Antarctica. Regarding the significance of the trends, NCEP1
and NCEP2 differ considerably from the observational datasets by strongly
exaggerating the warming trends. In contrast, ERA-Interim gives reliable
results at most stations except at Amundsen-Scott where it shows a significant
cooling trend.Comment: 8 pages, 5 figure
Diagnostics From Three Rising Submillimeter Bursts
In the paper we investigate three novel rising submillimeter (THz) bursts
occurred sequentially in a super-Active Region NOAA 10486. The average rising
rate of the flux density above 200 GHz is only 20 sfu/GHz (corresponding
spectral index of 1.6) for the THz spectral components of 2003 October
28 and November 4 bursts, while it can attain values of 235 sfu/GHz
(=4.8) for 2003 November 2 burst. The steeply rising THz spectrum can
be produced by a population of high relativistic electrons with a low-energy
cutoff of 1 MeV , while it only requires a low-energy cutoff of 30 keV for the
two slowly rising THz bursts, via gyrosynchrotron (GS) radiation based on our
numerical simulations of burst spectra in the magnetic dipole field case. The
electron density variation is much larger in the THz source than that in
microwave (MW) one. It is interesting that the THz source radius decreased by
20--50 during the decay phase for the three events, but the MW one
increased by 28 for the 2003 November 2 event. In the paper we will present
a calculation formula of energy released by ultrarelativistic electrons,
accounting the relativistic correction for the first time. We find that the
energy released by energetic electrons in the THz source exceeds that in
microwave one due to the strong GS radiation loss at THz range, although the
modeled THz source area is 3--4 orders smaller than the modeled MW one. The
total energies released by energetic electrons via the GS radiation in radio
sources are estimated, respectively, to be ,
and erg for the October 28, November 2
and 4 bursts, which are 131, 76 and 4 times as large as the thermal energies of
, and erg estimated
from the soft x-ray GOES observations
Finding a Nonnegative Solution to an M-Tensor Equation
We are concerned with the tensor equation with an M-tensor or Z-tensor, which
we call the M- tensor equation or Z-tensor equation respectively. We derive a
necessary and sufficient condition for a Z (or M)-tensor equation to have
nonnegative solutions. We then develop a monotone iterative method to find a
nonnegative solution to an M-tensor equation. The method can be regarded as an
approximation to Newton's method for solving the equation. At each iteration,
we solve a system of linear equations. An advantage of the proposed method is
that the coefficient matrices of the linear systems are independent of the
iteration. We show that if the initial point is appropriately chosen, then the
sequence of iterates generated by the method converges to a nonnegative
solution of the M- tensor equation monotonically and linearly. At last, we do
numerical experiments to test the proposed methods. The results show the
efficiency of the proposed methods
Differences in Halo-Scale Environments between Type 1 and Type 2 AGNs at Low Redshift
Using low-redshift (z<0.09) samples of AGNs, normal galaxies and groups of
galaxies selected from the Sloan Digital Sky Survey (SDSS), we study the
environments of type 1 and type 2 AGNs both on small and large scales.
Comparisons are made for galaxy samples matched in redshift, -band
luminosity, [OIII] luminosity, and also the position in groups (central or
satellite). We find that type 2 AGNs and normal galaxies reside in similar
environments. Type 1 and type 2 AGNs have similar clustering properties on
large scales (Mpc), but at scales smaller than 100 kpc, type 2s have
significant more neighbors than type 1s ( times more for central
AGNs at kpc). These results suggest that type 1 and type 2 AGNs are
hosted by halos of similar masses, as is also seen directly from the mass
distributions of their host groups ( for centrals
and for satellites). Type~2s have significantly
more satellites around them, and the distribution of their satellites is also
more centrally concentrated. The host galaxies of both types of AGNs have
similar optical properties, but their infrared colors are significantly
different. Our results suggest that the simple unified model based solely on
torus orientation is not sufficient, but that galaxy interactions in dark
matter halos must have played an important role in the formation of the dust
structure that obscures AGNs.Comment: accepted for publication in ApJ, 12 pages, 9 figures, 1 tabl
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