7,030 research outputs found
Dark viscous fluid described by a unified equation of state in cosmology
We generalize the CDM model by introducing a unified EOS to describe
the Universe contents modeled as dark viscous fluid, motivated by the fact that
a single constant equation of state (EOS) () reproduces the
CDM model exactly. This EOS describes the perfect fluid term, the
dissipative effect, and the cosmological constant in a unique framework and the
Friedmann equations can be analytically solved. Especially, we find a relation
between the EOS parameter and the renormalizable condition of a scalar field.
We develop a completely numerical method to perform a minimization to
constrain the parameters in a cosmological model directly from the Friedmann
equations, and employ the SNe data with the parameter measured
from the SDSS data to constrain our model. The result indicates that the
dissipative effect is rather small in the late-time Universe.Comment: 4 pages, 2 figures. v2: new materials added. v3: matches the version
to appear in IJMP
Historical Expressions and Comprehension in Visual Materials : A Reading of \u27\u27Pictorial Record of the Mongol Invasion\u27\u27
Historical Consciousness, Historiography, and Modern Japanese Values, 2002年10月末-11月, カナダ, アルバータ州バン
Universal scheme to generate metal-insulator transition in disordered systems
We propose a scheme to generate metal-insulator transition in random binary
layer (RBL) model, which is constructed by randomly assigning two types of
layers. Based on a tight-binding Hamiltonian, the localization length is
calculated for a variety of RBLs with different cross section geometries by
using the transfer-matrix method. Both analytical and numerical results show
that a band of extended states could appear in the RBLs and the systems behave
as metals by properly tuning the model parameters, due to the existence of a
completely ordered subband, leading to a metal-insulator transition in
parameter space. Furthermore, the extended states are irrespective of the
diagonal and off-diagonal disorder strengths. Our results can be generalized to
two- and three-dimensional disordered systems with arbitrary layer structures,
and may be realized in Bose-Einstein condensates.Comment: 5 ages, 4 figure
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