13,082 research outputs found
K-essence Explains a Lorentz Violation Experiment
Recently, a state of the art experiment shows evidence for Lorentz violation
in the gravitational sector. To explain this experiment, we investigate a
spontaneous Lorentz violation scenario with a generalized scalar field. We find
that when the scalar field is nonminimally coupled to gravity, the Lorentz
violation induces a deformation in the Newtonian potential along the direction
of Lorentz violation.Comment: 8 pages, the final version, discussion and references adde
A Hybrid Quantum Encoding Algorithm of Vector Quantization for Image Compression
Many classical encoding algorithms of Vector Quantization (VQ) of image
compression that can obtain global optimal solution have computational
complexity O(N). A pure quantum VQ encoding algorithm with probability of
success near 100% has been proposed, that performs operations 45sqrt(N) times
approximately. In this paper, a hybrid quantum VQ encoding algorithm between
classical method and quantum algorithm is presented. The number of its
operations is less than sqrt(N) for most images, and it is more efficient than
the pure quantum algorithm.
Key Words: Vector Quantization, Grover's Algorithm, Image Compression,
Quantum AlgorithmComment: Modify on June 21. 10pages, 3 figure
Magneto-structural coupling and harmonic lattice dynamics in CaFeAs probed by M\"ossbauer spectroscopy
In this paper we present detailed M\"ossbauer spectroscopy study of
structural and magnetic properties of the undoped parent compound
CaFeAs single crystal. By fitting the temperature dependence of the
hyperfine magnetic field we show that the magneto-structural phase transition
is clearly first-order in nature and we also deduced the compressibility of our
sample to be . Within the Landau's theory of phase
transition, we further argue that the observed phase transition may stem from
the strong magneto-structural coupling effect. Temperature dependence of the
Lamb-M\"ossbauer factor show that the paramagnetic phase and the
antiferromagnetic phase exhibit similar lattice dynamics in high frequency
modes with very close Debye temperatures, 270\,K.Comment: 6 pages,5 figures Accepted by J. Phys.: Condens. Matte
Opinion Mining on Non-English Short Text
As the type and the number of such venues increase, automated analysis of
sentiment on textual resources has become an essential data mining task. In
this paper, we investigate the problem of mining opinions on the collection of
informal short texts. Both positive and negative sentiment strength of texts
are detected. We focus on a non-English language that has few resources for
text mining. This approach would help enhance the sentiment analysis in
languages where a list of opinionated words does not exist. We propose a new
method projects the text into dense and low dimensional feature vectors
according to the sentiment strength of the words. We detect the mixture of
positive and negative sentiments on a multi-variant scale. Empirical evaluation
of the proposed framework on Turkish tweets shows that our approach gets good
results for opinion mining
Ferromagnetism in the Infinite-U Hubbard Model
We have studied the stability of the ferromagnetic state in the infinite-U
Hubbard model on a square lattice by approximate diagonalization of finite
lattices using the density matrix renormalization group technique. By studying
lattices with up to 5X20 sites, we have found the ferromagnetic state to be
stable below the hole density of 22 percent. Beyond 22 percent of hole doping,
the total spin of the ground state decreased gradually to zero with increasing
hole density.Comment: 13 pages, RevteX 3.0, seven figures appended in uuencoded form,
correcting problems with uuencoded figure
Quasi-compactons in inverted nonlinear photonic crystals
We study large-amplitude one-dimensional solitary waves in photonic crystals
featuring competition between linear and nonlinear lattices, with minima of the
linear potential coinciding with maxima of the nonlinear pseudopotential, and
vice versa (inverted nonlinear photonic crystals, INPhCs), in the case of the
saturable self-focusing nonlinearity. Such crystals were recently fabricated
using a mixture of SU-8 and Rhodamine-B optical materials. By means of
numerical methods and analytical approximations, we find that large-amplitude
solitons are broad sharply localized stable pulses (quasi-compactons, QCs).
With the increase of the totalpower, P, the QC's centroid performs multiple
switchings between minima and maxima of the linear potential. Unlike cubic
INPhCs, the large-amplitude solitons are mobile in the medium with the
saturable nonlinearity. The threshold value of the kick necessary to set the
soliton in motion is found as a function of P. Collisions between moving QCs
are considered too.Comment: 11 pages, 8 figures, Physical Review A, in pres
Are spectroscopic factors from transfer reactions consistent with asymptotic normalisation coefficients?
It is extremely important to devise a reliable method to extract
spectroscopic factors from transfer cross sections. We analyse the standard
DWBA procedure and combine it with the asymptotic normalisation coefficient,
extracted from an independent data set. We find that the single particle
parameters used in the past generate inconsistent asymptotic normalization
coefficients. In order to obtain a consistent spectroscopic factor,
non-standard parameters for the single particle overlap functions can be used
but, as a consequence, often reduced spectroscopic strengths emerge. Different
choices of optical potentials and higher order effects in the reaction model
are also studied. Our test cases consist of: C(d,p)C(g.s.) at
MeV, O(d,p)O(g.s.) at MeV and
Ca(d,p)Ca(g.s.) at MeV. We underline the
importance of performing experiments specifically designed to extract ANCs for
these systems.Comment: 15 pages, 12 figures, Phys. Rev. C (in press
Born-Infeld Black Holes in (A)dS Spaces
We study some exact solutions in a -dimensional Einstein-Born-Infeld
theory with a cosmological constant. These solutions are asymptotically de
Sitter or anti-de Sitter, depending on the sign of the cosmological constant.
Black hole horizon and cosmological horizon in these spacetimes can be a
positive, zero or negative constant curvature hypersurface. We discuss the
thermodynamics associated with black hole horizon and cosmological horizon. In
particular we find that for the Born-Infeld black holes with Ricci flat or
hyperbolic horizon in AdS space, they are always thermodynamically stable, and
that for the case with a positive constant curvature, there is a critical value
for the Born-Infeld parameter, above which the black hole is also always
thermodynamically stable, and below which a unstable black hole phase appears.
In addition, we show that although the Born-Infeld electrodynamics is
non-linear, both black hole horizon entropy and cosmological horizon entropy
can be expressed in terms of the Cardy-Verlinde formula. We also find a
factorized solution in the Einstein-Born-Infeld theory, which is a direct
product of two constant curvature spaces: one is a two-dimensional de Sitter or
anti-de Sitter space, the other is a ()-dimensional positive, zero or
negative constant curvature space.Comment: Latex, 18 pages with 4 eps figures, v2: Revtex, 11 pages with 4 eps
figures, to appear in PR
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