3,481 research outputs found
Reissner-Nordstr\"om Metric in the Friedman-Robertson-Walker Universe
The metric for a Reissner-Nordstrm black hole in the background of
the Friedman-Robertson-Walker universe is obtained. Then we verified it and
discussed the influence of the evolution of the universe on the size of the
black hole. To study the problem of the orbits of a planet in the expanding
universe, we rewrote the metric in the Schwarzschild coordinates system and
deduced the equation of motion for a planet.Comment: 8 pages, no figure
ATRank: An Attention-Based User Behavior Modeling Framework for Recommendation
A user can be represented as what he/she does along the history. A common way
to deal with the user modeling problem is to manually extract all kinds of
aggregated features over the heterogeneous behaviors, which may fail to fully
represent the data itself due to limited human instinct. Recent works usually
use RNN-based methods to give an overall embedding of a behavior sequence,
which then could be exploited by the downstream applications. However, this can
only preserve very limited information, or aggregated memories of a person.
When a downstream application requires to facilitate the modeled user features,
it may lose the integrity of the specific highly correlated behavior of the
user, and introduce noises derived from unrelated behaviors. This paper
proposes an attention based user behavior modeling framework called ATRank,
which we mainly use for recommendation tasks. Heterogeneous user behaviors are
considered in our model that we project all types of behaviors into multiple
latent semantic spaces, where influence can be made among the behaviors via
self-attention. Downstream applications then can use the user behavior vectors
via vanilla attention. Experiments show that ATRank can achieve better
performance and faster training process. We further explore ATRank to use one
unified model to predict different types of user behaviors at the same time,
showing a comparable performance with the highly optimized individual models.Comment: AAAI 201
Dilaton Black Holes in de Sitter or Anti-de Sitter Universe
Poletti and Wiltshire have shown that, with the exception of a pure
cosmological constant, the solution of a dilaton black hole in the background
of de Sitter or anti-de Sitter universe, does not exist in the presence of one
Liouville-type dilaton potential. Here with the combination of three
Liouville-type dilaton potentials, we obtain the dilaton black hole solutions
in the background of de Sitter or anti-de Sitter universe.Comment: 13 pages,to appear in Phys. Rev.
Higher Dimensional Dilaton Black Holes with Cosmological Constant
The metric of a higher-dimensional dilaton black hole in the presence of a
cosmological constant is constructed. It is found that the cosmological
constant is coupled to the dilaton in a non-trivial way. The dilaton potential
with respect to the cosmological constant consists of three Liouville-type
potentials.Comment: 8 pages,to appear in Phys. Lett.
Arbitrary Dimensional Schwarzschild-FRW Black Holes
The metric of arbitrary dimensional Schwarzschild black hole in the
background of Friedman-Robertson-Walker universe is presented in the cosmic
coordinates system. In particular, the arbitrary dimensional Schwarzschild-de
Sitter metric is rewritten in the Schwarzschild coordinates system and basing
on which the even more generalized higher dimensional Schwarzschild-de Sitter
metric with another extra dimensions is found. The generalized solution shows
that the cosmological constant may roots in the extra dimensions of space.Comment: 10 page
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