8,179 research outputs found
Ordering-sensitive and Semantic-aware Topic Modeling
Topic modeling of textual corpora is an important and challenging problem. In
most previous work, the "bag-of-words" assumption is usually made which ignores
the ordering of words. This assumption simplifies the computation, but it
unrealistically loses the ordering information and the semantic of words in the
context. In this paper, we present a Gaussian Mixture Neural Topic Model
(GMNTM) which incorporates both the ordering of words and the semantic meaning
of sentences into topic modeling. Specifically, we represent each topic as a
cluster of multi-dimensional vectors and embed the corpus into a collection of
vectors generated by the Gaussian mixture model. Each word is affected not only
by its topic, but also by the embedding vector of its surrounding words and the
context. The Gaussian mixture components and the topic of documents, sentences
and words can be learnt jointly. Extensive experiments show that our model can
learn better topics and more accurate word distributions for each topic.
Quantitatively, comparing to state-of-the-art topic modeling approaches, GMNTM
obtains significantly better performance in terms of perplexity, retrieval
accuracy and classification accuracy.Comment: To appear in proceedings of AAAI 201
The Spectrum of a Binding System for a Heavy Quark with an Anti-Sbottom or for a Sbottom and Anti-Sbottom Pair
Since long-lived light bottom squark (sbottom) and its anti-particle with a
mass close to the bottom quark have not been excluded by experiments so far, we
consider such a sbottom to combine with its anti-particle to form a color
singlet meson-like bound state or to combine with a common anti-quark to form a
fermion-like one, or accordingly their anti-particles to form an anti-particle
bound system. Namely we calculate the low-lying spectrum of the systems based
on QCD inspired potential model. To be as relativistic as possible, we start
with the framework of Bethe-Salpeter (BS) equation even for non-relativistic
binding systems. Finally, we obtain the requested spectrum by constructing
general forms of the BS wave functions and solving the BS equations under
instantaneous approximation.Comment: 13 pages, 1 figur
Spectral and optical properties in the antiphase stripe phase of the cuprate superconductors
We investigate the superconducting order parameter, the spectral and optical
properties in a stripe model with spin (charge) domain-derived scattering
potential (). We show that the charge domain-derived scattering
is less effective than the spin scattering on the suppression of
superconductivity. For , the spectral weight concentrates on
the () antinodal region, and a finite energy peak appears in the optical
conductivity with the disappearance of the Drude peak. But for , the spectral weight concentrates on the () nodal region,
and a residual Drude peak exists in the optical conductivity without the finite
energy peak. These results consistently account for the divergent observations
in the ARPES and optical conductivity experiments in several high-
cuprates, and suggest that the "insulating" and "metallic" properties are
intrinsic to the stripe state, depending on the relative strength of the spin
and charge domain-derived scattering potentials.Comment: 7 pages, 4 figure
Coexistence of the antiferromagnetic and superconducting order and its effect on spin dynamics in electron-doped high- cuprates
In the framework of the slave-boson approach to the model, it is
found that for electron-doped high- cuprates, the staggered
antiferromagnetic (AF) order coexists with superconducting (SC) order in a wide
doping level ranged from underdoped to nearly optimal doping at the mean-field
level. In the coexisting phase, it is revealed that the spin response is
commensurate in a substantial frequency range below a crossover frequency
for all dopings considered, and it switches to the incommensurate
structure when the frequency is higher than . This result is in
agreement with the experimental measurements. Comparison of the spin response
between the coexisting phase and the pure SC phase with a
-wave pairing plus a higher harmonics term (DP+HH) suggests
that the inclusion of the two-band effect is important to consistently account
for both the dispersion of the spin response and the non-monotonic gap behavior
in the electron-doped cuprates.Comment: 6 pages, 5 figure
Black Hole Hyperaccretion Inflow-outflow Model. I. Long And Ultra-long Gamma-ray Bursts
Long-duration gamma-ray bursts (LGRBs) and ultra-LGRBs (ULGRBs) originate from collapsars, in the center of which a newborn rotating stellar-mass black hole (BH) surrounded by a massive accretion disk may form. In the scenario of the BH hyperaccretion inflow-outflow model and Blandford-Znajek (BZ) mechanism to trigger gamma-ray bursts (GRBs), the real accretion rate to power a BZ jet is far lower than the mass supply rate from the progenitor star. The characteristics of the progenitor stars can be constrained by GRB luminosity observations, and the results exceed usual expectations. LGRBs lasting from several seconds to tens of seconds in the rest frame may originate from solar-metallicity (Z ∼ 1 Z⊙, where Z and Z⊙ are the metallicities of progenitor stars and the Sun), massive (M ≳ 34 M⊙, where M and M⊙ are the masses of progenitor stars and the Sun) stars or some zerometallicity (Z ∼ 0) stars. A fraction of low-metallicity (Z ≲ 10-2Z⊙) stars, including Population III stars, can produce ULGRBs such as GRB 111209A. The fraction of LGRBs lasting less than tens of seconds in the rest frame is more than 40%, which cannot conform to the fraction of the demanded type of progenitor star. It possibly implies that the activity timescale of the central engine may be much longer than the observed timescale of prompt emission phase, as indicated by X-ray late-time activities. Alternatively, LGRBs and ULGRBs may be powered by a millisecond magnetar central engine. © 2017. The American Astronomical Society. All rights reserved
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