27,418 research outputs found
Friedmann cosmology on codimension 2 brane with time dependent tension
A solution of codimension 2 brane is found for which 4 dimensional Friedmann
cosmology is recovered on the brane with time dependent tension, in the
Einstein frame. The effective parameter of equation of state on the
brane can be quintessence like, de Sitter like or phantom like, depending on
integration constants of the solution.Comment: 6 pages, 4 figure
Stable Fulde-Ferrell-Larkin-Ovchinnikov pairing states in 2D and 3D optical lattices
We present the study of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing
states in the -orbital bands in both two and three-dimensional optical
lattices. Due to the quasi one-dimensional band structure which arises from the
unidirectional hopping of the orthogonal -orbitals, the pairing phase space
is not affected by spin imbalance. Furthermore, interactions build up high
dimensional phase coherence which stabilizes the FFLO states in 2D and 3D
optical lattices in a large parameter regime in phase diagram. These FFLO
phases are stable with imposing the inhomogeneous trapping potential. Their
entropies are comparable to those of the normal states at finite temperatures.Comment: 5 page
Numerical Investigation on Flow Separation Control of Low Reynolds Number Sinusoidal Aerofoils
The paper presents a computational analysis of the characteristics of a NACA 634-
021 aerofoil incorporated with sinusoidal leading-edge protuberances at Re = 14,000.
The protuberances are characterized by an amplitude and wavelength of 12% and 50%
of the aerofoil chord length respectively. An unsteady Reynolds Average Navier Stokes
(RANS) analysis of the full-span aerofoils was carried out using Transition SST (Shear
Stress Transport) turbulence model across five different angles-of-attack (AOA).
Comparisons with previous experimental results reported good qualitative agreements
in terms of flow separation when the aerofoils are pitched at higher AOAs. Results
presented here comprised of near-wall flow visualizations of the flow separation bubble
at the peaks and troughs of the protuberances. Additionally, results indicate that the
aerofoil with leading-edge protuberances displayed distinctive wall shear streamline and
iso-contour characteristics at different span-wise positions. This implies that even at a
low Reynolds number, implementations of these leading-edge protuberances could have
positive or adverse effects on flow separation
Weak productions of new charmonium in semi-leptonic decays of B_c
We study the weak productions of novel heavy mesons, such as
, , , , X(3940),
Y(3940), X(3872), and Y(4260), in the semi-leptonic decays. Since there
is still no definite answer for the components of X(3940), Y(3940), X(3872),
Y(4260) so far, we will assign them as excited charmonium states with the
possible quantum numbers constrained by the current experiments. As for the
weak transition form factors, we calculate them in the framework of light-cone
QCD sum rules approach, which is proved to be a powerful tool to deal with the
non-perturbative hadronic matrix element. Our results indicate that different
interpretations of X(3940) can result in remarkable discrepancy of the
production rate in the decays, which would help to clarify the inner
structure of the X(3940) with the forthcoming LHC-b experiments. Besides, the
predicted large weak production rates of X(3872) and Y(3940) in decays
and the small semi-leptonic decay rate for all depend on
their quantum number assignments. Moreover, the mixing of
various vector charmonium states in the weak decay of is also discussed
in this work. The future experimental measurements of these decays will test
the inner structures of these particles, according to our predictions here.Comment: 26 pages, with 7 figures, revTex
The double charm decays of Meson in the Perturbative QCD Approach
We make a systematic investigation on the double charm decays of meson,
by employing the perturbative QCD approach based on factorization. It is
found that the non-factorizable emission diagrams are not negligible in these
channels. We predict the branching ratios of these decays and also the
transverse polarization fractions of decays, % where V denote the vector meson.
We find that the magnitudes of the branching ratios of the decays
and are very close to
each other, which are well suited to extract the Cabibbo-Kobayashi-Maskawa
angle through the amplitude relations. In addition, a large transverse
polarization contribution that can reach is predicted in some of
the meson decay to two vector charmed mesons.Comment: 22 pages, 5 tables, to appear at PRD. arXiv admin note: text overlap
with arXiv:1112.125
Thermodynamic of the Ghost Dark Energy Universe
Recently, the vacuum energy of the QCD ghost in a time-dependent background
is proposed as a kind of dark energy candidate to explain the acceleration of
the Universe. In this model, the energy density of the dark energy is
proportional to the Hubble parameter , which is the Hawking temperature on
the Hubble horizon of the Friedmann-Robertson-Walker (FRW) Universe. In this
paper, we generalized this model and choice the Hawking temperature on the
so-called trapping horizon, which will coincides with the Hubble temperature in
the context of flat FRW Universe dominated by the dark energy component. We
study the thermodynamics of Universe with this kind of dark energy and find
that the entropy-area relation is modified, namely, there is an another new
term besides the area term.Comment: 8 pages, no figure
Recommendatory system for supermarket online shopping
With the recent rise of online purchasing, many companies have focused on developing recommendation systems, where customers are suggested different options for complementing their purchases. This thesis will introduce and test four different approaches for a recommendation system for online shopping at supermarkets, based on the historical of previous customers. The four proposed algorithms are based on successful recommendation systems, which include a histogram-based approach, a graph theory-based approach, an embedding-based approach and finally a support-vector machine-based approach
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