484 research outputs found
Image classification by visual bag-of-words refinement and reduction
This paper presents a new framework for visual bag-of-words (BOW) refinement
and reduction to overcome the drawbacks associated with the visual BOW model
which has been widely used for image classification. Although very influential
in the literature, the traditional visual BOW model has two distinct drawbacks.
Firstly, for efficiency purposes, the visual vocabulary is commonly constructed
by directly clustering the low-level visual feature vectors extracted from
local keypoints, without considering the high-level semantics of images. That
is, the visual BOW model still suffers from the semantic gap, and thus may lead
to significant performance degradation in more challenging tasks (e.g. social
image classification). Secondly, typically thousands of visual words are
generated to obtain better performance on a relatively large image dataset. Due
to such large vocabulary size, the subsequent image classification may take
sheer amount of time. To overcome the first drawback, we develop a graph-based
method for visual BOW refinement by exploiting the tags (easy to access
although noisy) of social images. More notably, for efficient image
classification, we further reduce the refined visual BOW model to a much
smaller size through semantic spectral clustering. Extensive experimental
results show the promising performance of the proposed framework for visual BOW
refinement and reduction
Unstable Galaxy Models
The dynamics of collisionless galaxy can be described by the Vlasov-Poisson
system. By the Jean's theorem, all the spherically symmetric steady galaxy
models are given by a distribution of {\Phi}(E,L), where E is the particle
energy and L the angular momentum. In a celebrated Doremus-Feix-Baumann
Theorem, the galaxy model {\Phi}(E,L) is stable if the distribution {\Phi} is
monotonically decreasing with respect to the particle energy E. On the other
hand, the stability of {\Phi}(E,L) remains largely open otherwise. Based on a
recent abstract instability criterion of Guo-Lin, we constuct examples of
unstable galaxy models of f(E,L) and f(E) in which f fails to be monotone in E
Stability of rotating gaseous stars
We consider stability of rotating gaseous stars modeled by the Euler-Poisson
system with general equation of states. When the angular velocity of the star
is Rayleigh stable, we proved a sharp stability criterion for axi-symmetric
perturbations. We also obtained estimates for the number of unstable modes and
exponential trichotomy for the linearized Euler-Poisson system. By using this
stability criterion, we proved that for a family of slowly rotating stars
parameterized by the center density with fixed angular velocity profile, the
turning point principle is not true. That is, unlike the case of non-rotating
stars, the change of stability of the rotating stars does not occur at extrema
points of the total mass. By contrast, we proved that the turning point
principle is true for the family of slowly rotating stars with fixed angular
momentum distribution. When the angular velocity is Rayleigh unstable, we
proved linear instability of rotating stars. Moreover, we gave a complete
description of the spectra and sharp growth estimates for the linearized
Euler-Poisson equation.Comment: Minor corrections of typo
A Research on Tourism E-Business of Shanxi
E-business has become a new growth point of current economic development in the world. The natural adaptability between tourism and E-business gives birth to tourism E-business. The tourism resources in Shanxi are unique, yet its tourism development level and the abundant resources are not harmonious. To transform its resource advantage into economic advantage, developing tourism E-business is very urgent and necessary. In this article, through quantitative analysis and qualitative analysis methods, we find out the problems existing in the development of tourism E-business in Shanxi, and put forward corresponding development measures, especially the mobile E-tourism based on 3G technology, which is a new pattern and will become the development direction of Shanxi’s tourism E-business in the future. The research aims at providing practical references for the tourism management departments and enterprises in Shanxi to enhance its competitiveness and promote its sustainable development
Dynamical magneto-rotational instability
Magneto-rotational instability (MRI) is an important instability mechanism
for rotating flows with magnetic fields. In particular, when the strength of
the magnetic field tends to zero, the stability criterion for rotating flows is
generally different from the classical Rayleigh criterion for rotating flows
without a magnetic field. MRI has wide applications in astrophysics,
particularly to the turbulence and enhanced angular momentum transport in
accretion disks. For the case of vertical magnetic fields, we give rigorous
proof of linear MRI and a complete description of the spectra and semigroup
growth of the linearized operator. Moreover, we prove nonlinear stability and
instability from the sharp linear stability/instability criteria
Nonlinear stability of non-rotating gaseous stars
For the non-rotating gaseous stars modeled by the compressible Euler-Poisson
system with general pressure law, Lin and Zeng [18] proved a turning point
principle, which gives the sharp linear stability/instability criteria for the
non-rotating gaseous stars. In this paper, we prove that the sharp linear
stability criterion for the non-rotating stars also implies nonlinear orbital
stability against general perturbations provided the global weak solutions
exist. If the perturbations are further restricted to be spherically symmetric,
then nonlinear stability holds true unconditionally in the sense that the
existence of global weak solutions near the non-rotating star can be proved.Comment: 30 page
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