8,947 research outputs found
Structure and growth process of vapor-grown carbon fibers
The structure, effect of heat, and growth process of vapor-grown carbon fibers are investigated. The growth process of the carbon fibers could be divided into three stages; nucleation, elongation, and thickening processes. Also, a multi-layered structure can be produced as well as graphitization
Universality of massive scalar field late-time tails in black-hole spacetimes
The late-time tails of a massive scalar field in the spacetime of black holes
are studied numerically. Previous analytical results for a Schwarzschild black
hole are confirmed: The late-time behavior of the field as recorded by a static
observer is given by , where
depends weakly on time. This result is carried over to the case of
a Kerr black hole. In particular, it is found that the power-law index of -5/6
depends on neither the multipole mode nor on the spin rate of the black
hole . In all black hole spacetimes, massive scalar fields have the same
late-time behavior irrespective of their initial data (i.e., angular
distribution). Their late-time behavior is universal.Comment: 11 pages, 14 figures, published versio
Theory for Photon-Assisted Macroscopic Quantum Tunneling in a Stack of Intrinsic Josephson Junctions
We propose a theory for photon-assisted macroscopic quantum tunneling (MQT)
in a stack of capacitively-coupled intrinsic Josephson junctions in which the
longitudinal Josephson plasma, i.e., longitudinal collective phase oscillation
modes, is excited. The scheme of energy-level quantization in the collective
oscillatory states is clarified in the -junction system. When the MQT occurs
from the single-plasmon states excited by microwave irradiation in the
multi-photon process to the uniform voltage state, our theory predicts that the
escape rate is proportional to . This result is consistent with the recent
observation in Bi-2212 intrinsic Josephson junctions.Comment: 5 pages, 2 figure
Voltage-biased I-V characteristics in the multi-Josephson junction model of high T superconductor
By use of the multi-Josephson junction model, we investigate voltage-biased
I-V characteristics. Differently from the case of the single junction, I-V
characteristics show a complicated behavior due to inter-layer couplings among
superconducting phase differences mediated by the charging effect. We show that
there exist three characteristic regions, which are identified by jumps and
cusps in the I-V curve. In the low voltage region, the total current is
periodic with trigonometric functional increases and rapid drops. Then a kind
of chaotic region is followed. Above certain voltage, the total current behaves
with a simple harmonic oscillation and the I-V characteristics form a
multi-branch structure as in the current-biased case. The above behavior is the
result of the inter-layer coupling, and may be used to confirm the inter-layer
coupling mechanism of the formation of hysteresis branches.Comment: 12 pages, Latex, 4 figure
Inflaton perturbations in brane-world cosmology with induced gravity
We study cosmological perturbations in the brane models with an induced
Einstein-Hilbert term on a brane. We consider an inflaton confined to a de
Sitter brane in a five-dimensional Minkowski spacetime. Inflaton fluctuations
excite Kaluza-Klein modes of bulk metric perturbations with mass and where is an
integer. There are two branches ( branches) of solutions for the
background spacetime. In the branch, which includes the self-accelerating
universe, a resonance appears for a mode with due to a spin-0
perturbation with . The self-accelerating universe has a distinct
feature because there is also a helicity-0 mode of spin-2 perturbations with
. In the branch, which can be thought as the Randall-Sundrum
type brane-world with the high energy quantum corrections, there is no
resonance. At high energies, we analytically confirm that four-dimensional
Einstein gravity is recovered, which is related to the disappearance of van
Dam-Veltman-Zakharov discontinuity in de Sitter spacetime.
On sufficiently small scales, we confirm that the lineariaed gravity on the
brane is well described by the Brans-Dicke theory with in
branch and in branch, respectively, which confirms the
existence of the ghost in branch. We also study large scale perturbations.
In branch, the resonance induces a non-trivial anisotropic stress on the
brane via the projection of Weyl tensor in the bulk, but no instability is
shown to exist on the brane.Comment: 20 pages, 4 figure
Fall vom Erfordernis der Erlaubnis zur Wiederbenutzung des Sonderabfallentsorgungsparks-Tokyo Obergericht Urteil vom 25. April 2007-
f(R) brane cosmology
Despite the nice features of the Dvali, Gabadadze and Porrati (DGP) model to
explain the late-time acceleration of the universe, it suffers from some
theoretical problems like the ghost issue. We present a way to self-accelerate
the normal DGP branch, which is known to be free of the ghost problem, by means
of an f(R) term on the brane action. We obtain the de Sitter self-accelerating
solutions of the model and study their stability under homogeneous
perturbations.Comment: 4 pages, 2 figures. Contribution to the proceedings of Spanish
Relativity Meeting 2009, Bilbao, Spain, 7-11 September 200
- …