22,156 research outputs found
Dynamical spacetimes in conformal gravity
The conformal gravity remarkably boosts our prehension of gravity theories.
We find a series of dynamical solutions in the -conformal gravity,
including generalized Schwarzschild-Friedmann-Robertson-Walker (GSFRW), charged
generalized Schwarzschild-Friedmann-Robertson-Walker (CGSFRW), especially
rotating Friedmann-Robertson-Walker (RFRW), charged rotating
Friedmann-Robertson-Walker (CRFRW), and a dynamical cylindrically symmetric
solutions. The RFRW, CRFRW and the dynamical cylindrically symmetric solutions
are never found in the Einstein gravity and modified gravities. The GSFRW and
CGSFRW solutions take different forms from the corresponding solutions in the
Einstein gravity.Comment: 13 pages, no fi
Theory for superconductivity in alkali chromium arsenides A2Cr3As3 (A=K,Rb,Cs)
We propose an extended Hubbard model with three molecular orbitals on a
hexagonal lattice with symmetry to study recently discovered
superconductivity in ACrAs (A=K,Rb,Cs). Effective pairing
interactions from paramagnon fluctuations are derived within the random phase
approximation, and are found to be most attractive in spin triplet channels. At
small Hubbard and moderate Hund's coupling, the pairing arises from
3-dimensional (3D) band and has a spatial symmetry
, which gives line nodes in the gap function. At large
, a fully gapped -wave state, dominates at the quasi-1D
-band
Adaptive model for recommendation of news
Most news recommender systems try to identify users' interests and news'
attributes and use them to obtain recommendations. Here we propose an adaptive
model which combines similarities in users' rating patterns with epidemic-like
spreading of news on an evolving network. We study the model by computer
agent-based simulations, measure its performance and discuss its robustness
against bias and malicious behavior. Subject to the approval fraction of news
recommended, the proposed model outperforms the widely adopted recommendation
of news according to their absolute or relative popularity. This model provides
a general social mechanism for recommender systems and may find its
applications also in other types of recommendation.Comment: 6 pages, 6 figure
Symmetry of superconducting states with two orbitals on a tetragonal lattice: application to
We use group theory to classify the superconducting states of systems with
two orbitals on a tetragonal lattice. The orbital part of the superconducting
gap function can be either symmetric or anti-symmetric. For the orbital
symmetric state, the parity is even for spin singlet and odd for spin triplet;
for the orbital anti-symmetric state, the parity is odd for spin singlet and
even for spin triplet. The gap basis functions are obtained with the use of the
group chain scheme by taking into account the spin-orbit coupling. In the weak
pairing limit, the orbital anti-symmetric state is only stable for the
degenerate orbitals. Possible application to iron-based superconductivity is
discussed.Comment: published versio
Solving the Cold-Start Problem in Recommender Systems with Social Tags
In this paper, based on the user-tag-object tripartite graphs, we propose a
recommendation algorithm, which considers social tags as an important role for
information retrieval. Besides its low cost of computational time, the
experiment results of two real-world data sets, \emph{Del.icio.us} and
\emph{MovieLens}, show it can enhance the algorithmic accuracy and diversity.
Especially, it can obtain more personalized recommendation results when users
have diverse topics of tags. In addition, the numerical results on the
dependence of algorithmic accuracy indicates that the proposed algorithm is
particularly effective for small degree objects, which reminds us of the
well-known \emph{cold-start} problem in recommender systems. Further empirical
study shows that the proposed algorithm can significantly solve this problem in
social tagging systems with heterogeneous object degree distributions
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