2,709 research outputs found
Big Rip in SO(1,1) phantom universe
For the inverse linear potential, the SO(1,1) field behaves as phantom for
late time and the Big Rip will occur. The field approaches zero as time
approaches the Big Rip, here. For this potential the phantom equation of state
takes the late-time minimum . We give some discussions that the Big
Rip in the SO(1,1) model may be treated as either the transition point of
universe from expansion to extract phase or the final state. In the latter
picture of the universe, the field has the symmetry and the scale factor
possesses the symmetry, for which the SO(1,1) charge plays a
crucial role.Comment: 10 pages, 1 figur
Critical state of phantom universe
The late-time evolution behavior of the autonomous system in the SO(1,1) dark
energy model with power-law potential is studied. Big Rip may be a critical
point of the autonomous system. This means that such a Big Rip may be
considered as the middle state between the expanding and contracting phases of
phantom universe. This result is also valid for some special interactions
between matter and dark energy.Comment: 6 pages, revtex
Anomalous behavior of trapping in extended dendrimers with a perfect trap
Compact and extended dendrimers are two important classes of dendritic
polymers. The impact of the underlying structure of compact dendrimers on
dynamical processes has been much studied, yet the relation between the
dynamical and structural properties of extended dendrimers remains not well
understood. In this paper, we study the trapping problem in extended dendrimers
with generation-dependent segment lengths, which is different from that of
compact dendrimers where the length of the linear segments is fixed. We first
consider a particular case that the deep trap is located at the central node,
and derive an exact formula for the average trapping time (ATT) defined as the
average of the source-to-trap mean first passage time over all starting points.
Then, using the obtained result we deduce a closed-form expression for the ATT
to an arbitrary trap node, based on which we further obtain an explicit
solution to the ATT corresponding to the trapping issue with the trap uniformly
distributed in the polymer systems. We show that the trap location has a
substantial influence on the trapping efficiency measured by the ATT, which
increases with the shortest distance from the trap to the central node, a
phenomenon similar to that for compact dendrimers. In contrast to this
resemblance, the leading terms of ATTs for the three trapping problems differ
drastically between extended and compact dendrimers, with the trapping
processes in the extended dendrimers being less efficient than in compact
dendrimers
Extended corona product as an exactly tractable model for weighted heterogeneous networks
Various graph products and operations have been widely used to construct
complex networks with common properties of real-life systems. However, current
works mainly focus on designing models of binary networks, in spite of the fact
that many real networks can be better mimicked by heterogeneous weighted
networks. In this paper, we develop a corona product of two weighted graphs,
based on which and an observed updating mechanism of edge weight in real
networks, we propose a minimal generative model for inhomogeneous weighted
networks. We derive analytically relevant properties of the weighted network
model, including strength, weight and degree distributions, clustering
coefficient, degree correlations and diameter. These properties are in good
agreement with those observed in diverse real-world weighted networks. We then
determine all the eigenvalues and their corresponding multiplicities of the
transition probability matrix for random walks on the weighted networks.
Finally, we apply the obtained spectra to derive explicit expressions for mean
hitting time of random walks and weighted counting of spanning trees on the
weighted networks. Our model is an exactly solvable one, allowing to
analytically treat its structural and dynamical properties, which is thus a
good test-bed and an ideal substrate network for studying different dynamical
processes, in order to explore the impacts of heterogeneous weight distribution
on these processes
A Survey of Signed Network Mining in Social Media
Many real-world relations can be represented by signed networks with positive
and negative links, as a result of which signed network analysis has attracted
increasing attention from multiple disciplines. With the increasing prevalence
of social media networks, signed network analysis has evolved from developing
and measuring theories to mining tasks. In this article, we present a review of
mining signed networks in the context of social media and discuss some
promising research directions and new frontiers. We begin by giving basic
concepts and unique properties and principles of signed networks. Then we
classify and review tasks of signed network mining with representative
algorithms. We also delineate some tasks that have not been extensively studied
with formal definitions and also propose research directions to expand the
field of signed network mining.Comment: 37 page
Magnetic interactions in a proposed diluted magnetic semiconductor (BaK)(ZnMn)P
By using first-principles electronic structure calculations, we have studied
the magnetic interactions in a proposed BaZnP-based diluted magnetic
semiconductor (DMS). For a typical compound
Ba(ZnMn)P with only spin doping, due to the
superexchange interaction between Mn atoms and the lack of itinerant carriers,
the short-range antiferromagnetic coupling dominates. Partially substituting K
atoms for Ba atoms, which introduces itinerant hole carriers into the
orbitals of P atoms so as to link distant Mn moments with the spin-polarized
hole carriers via the - hybridization between P and Mn atoms, is very
crucial for the appearance of ferromagnetism in the compound. Furthermore,
applying hydrostatic pressure first enhances and then decreases the
ferromagnetic coupling in
(BaK)(ZnMn)P at a turning point
around 15 GPa, which results from the combined effects of the pressure-induced
variations of electron delocalization and - hybridization. Compared with
the BaZnAs-based DMS, the substitution of P for As can modulate the
magnetic coupling effectively. Both the results for BaZnP-based and
BaZnAs-based DMSs demonstrate that the robust antiferromagnetic (AFM)
coupling between the nearest Mn-Mn pairs bridged by anions is harmful to
improving the performance of this II-II-V based DMS materials.Comment: 7 pages, 6 figures, 1 table; Accepted by Chinese Physics B (2018
Reconciling the light component and all-particle cosmic ray energy spectra at the knee
The knee phenomenon of the cosmic ray spectrum, which plays an important role
in studying the acceleration mechanism of cosmic rays, is still an unsolved
mystery. We try to reconcile the knee spectra measured by ARGO-YBJ and
Tibet-III. A simple broken power-law model fails to explain the experimental
data. Therefore a modified broken power-law model with non-linear acceleration
effects is adopted, which can describe the sharp knee structure. This model
predicts that heavy elements dominate at the knee.Comment: 5 pages, 5 figure
The power-law expansion universe and dark energy evolution
In order to depict the transition from deceleration to acceleration expansion
of the universe we use a power-law expansion scale factor, , with , and three parameters determined by ,
and . For the spatially flat, isotropic and homogeneous universe,
such a scale factor leads to the results that the dark energy density is slowly
changing currently, and predicts the equation of state changes from
to .Comment: 10 pages, 2 figure
The power-law expansion universe and the late-time behavior
Using the SNe Ia data we determine the three parameters in the power-law
expanding universe model with time-dependent power \cite{W}. Inputting
and , then we find the evolution curve with and
can fit very well to that from SNe observation data. The model
predicts the transition redshift . The dark energy deduced from
this model have phantom property but the universe doesn't encounter the Big Rip
singularity. Assuming that this model with the three parameters is valid for
the future universe, then we predict that the total energy density of the
universe is decreasing and will soon reach its minimum.Comment: 10 pages, 5 figure
Triplet Distillation for Deep Face Recognition
Convolutional neural networks (CNNs) have achieved a great success in face
recognition, which unfortunately comes at the cost of massive computation and
storage consumption. Many compact face recognition networks are thus proposed
to resolve this problem. Triplet loss is effective to further improve the
performance of those compact models. However, it normally employs a fixed
margin to all the samples, which neglects the informative similarity structures
between different identities. In this paper, we propose an enhanced version of
triplet loss, named triplet distillation, which exploits the capability of a
teacher model to transfer the similarity information to a small model by
adaptively varying the margin between positive and negative pairs. Experiments
on LFW, AgeDB, and CPLFW datasets show the merits of our method compared to the
original triplet loss.Comment: 5 pages, 2 tables, accpeted by ICML 2019 ODML-CDNNR Worksho
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