12,944 research outputs found
Holographic Derivation of Entanglement Entropy from AdS/CFT
A holographic derivation of the entanglement entropy in quantum (conformal)
field theories is proposed from AdS/CFT correspondence. We argue that the
entanglement entropy in d+1 dimensional conformal field theories can be
obtained from the area of d dimensional minimal surfaces in AdS_{d+2},
analogous to the Bekenstein-Hawking formula for black hole entropy. We show
that our proposal perfectly reproduces the correct entanglement entropy in 2D
CFT when applied to AdS_3. We also compare the entropy computed in AdS_5 \times
S^5 with that of the free N=4 super Yang-Mills.Comment: 5 pages, 3 figures, Revtex, references adde
Growth of Magnetic Fields Induced by Turbulent Motions
We present numerical simulations of driven magnetohydrodynamic (MHD)
turbulence with weak/moderate imposed magnetic fields. The main goal is to
clarify dynamics of magnetic field growth. We also investigate the effects of
the imposed magnetic fields on the MHD turbulence, including, as a limit, the
case of zero external field. Our findings are as follows. First, when we start
off simulations with weak mean magnetic field only (or with small scale random
field with zero imposed field), we observe that there is a stage at which
magnetic energy density grows linearly with time. Runs with different numerical
resolutions and/or different simulation parameters show consistent results for
the growth rate at the linear stage. Second, we find that, when the strength of
the external field increases, the equilibrium kinetic energy density drops by
roughly the product of the rms velocity and the strength of the external field.
The equilibrium magnetic energy density rises by roughly the same amount.
Third, when the external magnetic field is not very strong (say, less than ~0.2
times the rms velocity when measured in the units of Alfven speed), the
turbulence at large scales remains statistically isotropic, i.e. there is no
apparent global anisotropy of order B_0/v. We discuss implications of our
results on astrophysical fluids.Comment: 16 pages, 18 figures; ApJ, accepte
Disorder-induced metal-insulator transitions in three-dimensional topological insulators and superconductors
We discuss the effects of disorder in time-reversal invariant topological
insulators and superconductors in three spatial dimensions. For
three-dimensional topological insulator in symplectic (AII) symmetry class, the
phase diagram in the presence of disorder and a mass term, which drives a
transition between trivial and topological insulator phases, is computed
numerically by the transfer matrix method. The numerics is supplemented by a
field theory analysis (the large- expansion where is the number of
valleys or Dirac cones), from which we obtain the correlation length exponent,
and several anomalous dimensions at a non-trivial critical point separating a
metallic phase and a Dirac semi-metal. A similar field theory approach is
developed for disorder-driven transitions in symmetry class AIII, CI, and DIII.
For these three symmetry classes, where topological superconductors are
characterized by integer topological invariant, a complementary description is
given in terms of the non-linear sigma model supplemented with a topological
term which is a three-dimensional analogue of the Pruisken term in the integer
quantum Hall effect.Comment: 19 pages, 5 figure
Interacting topological phases and modular invariance
We discuss a (2+1) dimensional topological superconductor with left-
and right-moving Majorana edge modes and a
symmetry. In the absence of interactions, these phases are distinguished by an
integral topological invariant . With interactions, the edge state in the
case is unstable against interactions, and a invariant mass gap can be generated dynamically. We show that
this phenomenon is closely related to the modular invariance of type II
superstring theory. More generally, we show that the global gravitational
anomaly of the non-chiral Majorana edge states is the physical manifestation of
the bulk topological superconductors classified by .Comment: 11 page
Field-driven topological glass transition in a model flux line lattice
We show that the flux line lattice in a model layered HTSC becomes unstable
above a critical magnetic field with respect to a plastic deformation via
penetration of pairs of point-like disclination defects. The instability is
characterized by the competition between the elastic and the pinning energies
and is essentially assisted by softening of the lattice induced by a
dimensional crossover of the fluctuations as field increases. We confirm
through a computer simulation that this indeed may lead to a phase transition
from crystalline order at low fields to a topologically disordered phase at
higher fields. We propose that this mechanism provides a model of the low
temperature field--driven disordering transition observed in neutron
diffraction experiments on single crystals.Comment: 11 pages, 4 figures available upon request via snail mail from
[email protected]
Equation of State in Numerical Relativistic Hydrodynamics
Relativistic temperature of gas raises the issue of the equation of state
(EoS) in relativistic hydrodynamics. We study the EoS for numerical
relativistic hydrodynamics, and propose a new EoS that is simple and yet
approximates very closely the EoS of the single-component perfect gas in
relativistic regime. We also discuss the calculation of primitive variables
from conservative ones for the EoS's considered in the paper, and present the
eigenstructure of relativistic hydrodynamics for a general EoS, in a way that
they can be used to build numerical codes. Tests with a code based on the Total
Variation Diminishing (TVD) scheme are presented to highlight the differences
induced by different EoS's.Comment: To appear in the ApJS September 2006, v166n1 issue. Pdf with full
resolution figures can be downloaded from
http://canopus.cnu.ac.kr/ryu/ryuetal.pd
Three-dimensional structures of the tracheal systems of Anopheles sinensis and Aedes togoi pupae
Mosquitoes act as a vector for the transmission of disease. The World Health Organization has recommended strict control of mosquito larvae because of their few, fixed, and findable features. The respiratory system of mosquito larvae and pupae in the water has a weak point. As aquatic organisms, mosquito larvae and pupae inhale atmosphere oxygen. However, the mosquito pupae have a non-feeding stage, unlike the larvae. Therefore, detailed study on the tracheal system of mosquito pupae is helpful for understanding their survival strategy. In this study, the three-dimensional (3D) structures of the tracheal systems of Anopheles sinensis and Aedes togoi pupae were comparatively investigated using synchrotron X-ray microscopic computed tomography. The respiratory frequencies of the dorsal trunks were also investigated. Interestingly, the pupae of the two mosquito species possess special tracheal systems of which the morphological and functional features are distinctively different. The respiratory frequency of Ae. togoi is higher than that of An. sinensis. These differences in the breathing phenomena and 3D structures of the respiratory systems of these two mosquito species provide an insight into the tracheal systems of mosquito pupae. ? 2017 The Author(s).111Ysciescopu
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