10,159 research outputs found
Gravitational Radiation from a Naked Singularity -- Odd-Parity Perturbation --
It has been suggested that a naked singularity may be a good candidate for a
strong gravitational wave burster. The naked singularity occurs in the generic
collapse of an inhomogeneous dust ball. We study odd-parity mode of
gravitational waves from a naked singularity of the Lema\^{\i}tre-Tolman-Bondi
space-time. The wave equation for gravitational waves are solved by numerical
integration using the single null coordinate. The result is that the naked
singularity is not a strong source of the odd-parity gravitational radiation
although the metric perturbation grows in the central region. Therefore, the
Cauchy horizon in this space-time would be marginally stable against odd-parity
perturbations.Comment: 14 pages, 7 figures, to be published in Prog. Theor. Phys. Final
version, with minor changes. Reference 13 adde
Redox functionality mediated by adsorbed oxygen on a Pd-oxide film over a Pd(100) thin structure: A first-principles study
Stable oxygen sites on a PdO film over a Pd(100) thin structures with a
(sqrt{5} times sqrt{5}) R27^circ surface-unit cell are determined using the
first-principles electronic structure calculations with the generalized
gradient approximation. The adsorbed monatomic oxygen goes to a site bridging
two 2-fold-coordinated Pd atoms or to a site bridging a 2-fold-coordinated Pd
atom and a 4-fold-coordinated Pd atom. Estimated reaction energies of CO
oxidation by reduction of the oxidized PdO film and N_2O reduction mediated by
oxidation of the PdO film are exothermic. Motion of the adsorbed oxygen atom
between the two stable sites is evaluated using the nudged elastic band method,
where an energy barrier for a translational motion of the adsorbed oxygen may
become sim 0.45 eV, which is low enough to allow fluxionality of the surface
oxygen at high temperatures. The oxygen fluxionality is allowed by existence of
2-fold-coordinated Pd atoms on the PdO film, whose local structure has
similarity to that of Pd catalysts for the Suzuki-Miyaura cross coupling.
Although NO_x (including NO_2 and NO) reduction is not always catalyzed only by
the PdO film, we conclude that there may happen continual redox reactions
mediated by oxygen-adsorbed PdO films over a Pd surface structure, when the
influx of NO_x and CO continues, and when the reaction cycle is kept on a
well-designed oxygen surface.Comment: 15 pages, 6 figures, submitted to J. Phys. Condens. Matte
Exact transformation of a Langevin equation to a fluctuating response equation
We demonstrate that a Langevin equation that describes the motion of a
Brownian particle under non-equilibrium conditions can be exactly transformed
to a special equation that explicitly exhibits the response of the velocity to
a time dependent perturbation. This transformation is constructed on the basis
of an operator formulation originally used in nonlinear perturbation theory for
differential equations by extending it to stochastic analysis. We find that the
obtained expression is useful for the calculation of fundamental quantities of
the system, and that it provides a physical basis for the decomposition of the
forces in the Langevin description into effective driving, dissipative, and
random forces in a large-scale description.Comment: 14 pages, to appear in J. Phys. A: Math. Ge
N\'eel and Spin-Peierls ground states of two-dimensional SU(N) quantum antiferromagnets
The two-dimensional SU(N) quantum antiferromagnet, a generalization of the
quantum Heisenberg model, is investigated by quantum Monte Carlo simulations.
The ground state for is found to be of the N\'eel type with broken
SU(N) symmetry, whereas it is of the Spin-Peierls type for with broken
lattice translational invariance. No intermediate spin-liquid phase was
observed in contrast to previous numerical simulations on smaller lattices
[Santoro et al., Phys. Rev. Lett. {\bf 83} 3065 (1999)].Comment: 4 pages, 4 figure
RPA for Light-Front Hamiltonian Field Theory
A self-consistent random phase approximation (RPA) is proposed as an
effective Hamiltonian method in Light-Front Field Theory (LFFT). We apply the
general idea to the light-front massive Schwinger model to obtain a new bound
state equation and solve it numerically.Comment: A major revision in presentation, while the results essentially
unchanged. 2 figs. replaced, 1 fig. added, some parts of Sec. V moved to Sec.
IV, some wording changed, typos correcte
Gravitational Radiation from a Naked Singularity. II - Even-Parity Perturbation -
A naked singularity occurs in the generic collapse of an inhomogeneous dust
ball. We study the even-parity mode of gravitational waves from a naked
singularity of the Lema\^{\i}tre-Tolman-Bondi spacetime. The wave equations for
gravitational waves are solved by numerical integration using the single null
coordinate. The result implies that the metric perturbation grows when it
approaches the Cauchy horizon and diverges there, although the naked
singularity is not a strong source of even-parity gravitational radiation.
Therefore, the Cauchy horizon in this spacetime should be unstable with respect
to linear even-parity perturbations.Comment: 16 pages, 5 figures, errors and typos corrected, final versio
Diffusion in the Continuous-Imaginary-Time Quantum World-Line Monte Carlo Simulations with Extended Ensembles
The dynamics of samples in the continuous-imaginary-time quantum world-line
Monte Carlo simulations with extended ensembles are investigated. In the case
of a conventional flat ensemble on the one-dimensional quantum S=1 bi-quadratic
model, the asymmetric behavior of Monte Carlo samples appears in the diffusion
process in the space of the number of vertices. We prove that a local
diffusivity is asymptotically proportional to the number of vertices, and we
demonstrate the asymmetric behavior in the flat ensemble case. On the basis of
the asymptotic form, we propose the weight of an optimal ensemble as
, where denotes the number of vertices in a sample. It is shown
that the asymmetric behavior completely vanishes in the case of the proposed
ensemble on the one-dimensional quantum S=1 bi-quadratic model.Comment: 4 pages, 2 figures, update a referenc
Physical Processes in Naked Singularity Formation
Gravitational collapse is one of the most fruitful subjects in gravitational
physics. It is well known that singularity formation is inevitable in complete
gravitational collapse. It was conjectured that such a singularity should be
hidden by horizons if it is formed from generic initial data with physically
reasonable matter fields. Many possible counterexamples to this conjecture have
been proposed over the past three decades, although none of them has proved to
be sufficiently generic. In these examples, there appears a singularity that is
not hidden by horizons. This singularity is called a `naked singularity.' The
appearance of a naked singularity represents the formation of an observable
high-curvature, strong-gravity region. In this paper we review examples of
naked singularity formation and recent progress in research of observable
physical processes - gravitational radiation and quantum particle creation -
from a forming naked singularity.Comment: 76 pages, 25 figure file
Physical aspects of naked singularity explosion - How does a naked singularity explode? --
The behaviors of quantum stress tensor for the scalar field on the classical
background of spherical dust collapse is studied. In the previous works
diverging flux of quantum radiation was predicted. We use the exact expressions
in a 2D model formulated by Barve et al. Our present results show that the back
reaction does not become important during the semiclassical phase. The
appearance of the naked singularity would not be affected by this quantum field
radiation. To predict whether the naked singularity explosion occurs or not we
need the theory of quantum gravity. We depict the generation of the diverging
flux inside the collapsing star. The quantum energy is gathered around the
center positively. This would be converted to the diverging flux along the
Cauchy horizon. The ingoing negative flux crosses the Cauchy horizon. The
intensity of it is divergent only at the central naked singularity. This
diverging negative ingoing flux is balanced with the outgoing positive
diverging flux which propagates along the Cauchy horizon. After the replacement
of the naked singularity to the practical high density region the instantaneous
diverging radiation would change to more milder one with finite duration.Comment: 18 pages, 16 figure
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