1,809 research outputs found
New Charged Black Holes with Conformal Scalar Hair
A new class of four-dimensional, hairy, stationary solutions of the
Einstein-Maxwell-Lambda system with a conformally coupled scalar field is
constructed in this paper. The metric belongs to the Plebanski-Demianski family
and hence its static limit has the form of the charged C-metric. It is shown
that, in the static case, a new family of hairy black holes arises. They turn
out to be cohomogeneity-two, with horizons that are neither Einstein nor
homogenous manifolds. The conical singularities in the C-metric can be removed
due to the back reaction of the scalar field providing a new kind of regular,
radiative spacetime. The scalar field carries a continuous parameter
proportional to the usual acceleration present in the C-metric. In the
zero-acceleration limit, the static solution reduces to the dyonic
Bocharova-Bronnikov-Melnikov-Bekenstein solution or the dyonic extension of the
Martinez-Troncoso-Zanelli black holes, depending on the value of the
cosmological constant.Comment: Published versio
Kaluza-Klein black hole with negatively curved extra dimensions in string generated gravity models
We obtain a new exact black-hole solution in Einstein-Gauss-Bonnet gravity
with a cosmological constant which bears a specific relation to the
Gauss-Bonnet coupling constant. The spacetime is a product of the usual
4-dimensional manifold with a -dimensional space of constant negative
curvature, i.e., its topology is locally {\ma M}^n \approx {\ma M}^4 \times
{\ma H}^{n-4}. The solution has two parameters and asymptotically approximates
to the field of a charged black hole in anti-de Sitter spacetime. The most
interesting and remarkable feature is that the Gauss-Bonnet term acts like a
Maxwell source for large while at the other end it regularizes the metric
and weakens the central singularity.Comment: 4 pages, 2 figures, final version to appear in Physical Review D as a
rapid communicatio
Theory of quasiballistic transport through nanocrystalline silicon dots
A model to describe the underlying physics of high-energy electron emission from a porous silicon diode is presented. The model is based on an atomistic tight-binding method combined with semiclassical Monte Carlo simulation. It well reproduces essential features of experimental findings. An initial acceleration region is shown to play a crucial role in generating quasiballistic electron emission
Particle creation in Bose--Einstein condensates: Theoretical formulation based on conserving gapless mean field theory
We formulate particle creation phenomena in Bose--Einstein condensates in
terms of conserving gapless mean field theory for weakly interacting Bose
gases. The particle creation spectrum is calculated by rediagonalizing the
Bogoliubov--de Gennes (BdG) Hamiltonian in mean field theory. The conservation
implies that quasiparticle creation is accompanied by quantum backreaction to
the condensates. Particle creation in this mean field theory is found to be
equivalent to that in quantum field theory (QFT) in curved spacetime. An
expression is obtained for an effective metric affected by quantum
backreaction. The formula for the particle creation spectrum obtained in terms
of QFT in curved spacetime is shown to be the same as that given by
rediagonalizing the BdG Hamiltonian.Comment: 9 pages, typos correcte
Void-induced cross slip of screw dislocations in fcc copper
Pinning interaction between a screw dislocation and a void in fcc copper is
investigated by means of molecular dynamics simulation. A screw dislocation
bows out to undergo depinning on the original glide plane at low temperatures,
where the behavior of the depinning stress is consistent with that obtained by
a continuum model. If the temperature is higher than 300 K, the motion of a
screw dislocation is no longer restricted to a single glide plane due to cross
slip on the void surface. Several depinning mechanisms that involve multiple
glide planes are found. In particular, a depinning mechanism that produces an
intrinsic prismatic loop is found. We show that these complex depinning
mechanisms significantly increase the depinning stress
Superconductivity in undoped T' cuprates with Tc over 30 K
Undoped cuprates have long been considered to be antiferromagnetic
insulators. In this article, however, we report that superconductivity is
achieved in undoped T'-RE2CuO4 (RE = Pr, Nd, Sm, Eu, and Gd). Our discovery was
performed by using metal-organic decomposition (MOD), an inexpensive and
easy-to-implement thin-film process. The keys to prepare the superconducting
films are firing with low partial-pressure of oxygen and reduction at low
temperatures. The highest Tc of undoped T'-RE2CuO4 is over 30 K, substantially
higher than "electron-doped" analogs. Remarkably, Gd2CuO4, even the derivatives
of which have not shown superconductivity so far, gets superconducting with
Tconset as high as ~ 20 K. The implication of our discovery is briefly
discussed.Comment: 22 pages, 5 figures, submitted to Physical Review Letter
Quantum Kolmogorov Complexity and Quantum Key Distribution
We discuss the Bennett-Brassard 1984 (BB84) quantum key distribution protocol
in the light of quantum algorithmic information. While Shannon's information
theory needs a probability to define a notion of information, algorithmic
information theory does not need it and can assign a notion of information to
an individual object. The program length necessary to describe an object,
Kolmogorov complexity, plays the most fundamental role in the theory. In the
context of algorithmic information theory, we formulate a security criterion
for the quantum key distribution by using the quantum Kolmogorov complexity
that was recently defined by Vit\'anyi. We show that a simple BB84 protocol
indeed distribute a binary sequence between Alice and Bob that looks almost
random for Eve with a probability exponentially close to 1.Comment: typos correcte
Causality of the brane universe
Causal structure of the brane universe with respect to null geodesics in the
bulk spacetime is studied. It is pointed out that apparent causality violation
is possible for the brane universe which contains matter energy. It is also
shown that there is no 'horizon problem' in the Friedmann-Robertson-Walker
brane universe.Comment: LaTeX, 9 pages, 4 EPS figures to appear in Phys. Rev. Let
Compact Einstein Spaces based on Quaternionic K\"ahler Manifolds
We investigate the Einstein equation with a positive cosmological constant
for -dimensional metrics on bundles over Quaternionic K\"ahler base
manifolds whose fibers are 4-dimensional Bianchi IX manifolds. The Einstein
equations are reduced to a set of non-linear ordinary differential equations.
We numerically find inhomogeneous compact Einstein spaces with orbifold
singularity.Comment: LaTeX 28 pages, 5 eps figure
The use of desalinated-dried jellyfish and rice bran for controlling weeds and rice yield
To achieve higher rice production, rice-growing countries have used great amounts of synthetic chemical compounds (chemical fertilizers and pesticides) that can have adverse effects on the environment and humans. Organic products and organic farming technologies are friendlier to the environment and more conducive to sustainable agriculture but require different inputs, knowledge and skills. Weed control is one of the major challenges in organic rice cultivation. The present study proposes and tests the use of desalinated-dried jellyfish chips in the development of sustainable rice production. Vast amounts of jellyfishes have been found in the Sea of Japan (Nomura's jellyfish, Nemopilema nomurai Kishinouye) and Japan inland sea areas (Water jelly, Aurelia aurita (Linne)), and jellyfish populationc can have a negative impact on the fishery industry. In this context, the use of jellyfish in organic agriculture has attracted attention. The present study found that the application of desalinated-dried jellyfish (small pieces of jellyfish which are desalinated and dried) mixed in soil before transplanting can effectively control weeds in rice fields and has a nutrient effect because of the high nitrogen content (12-13%). Desalinated-dried jellyfish has potential as an agricultural material that replaces herbicides and chemical fertilizers. It also contributes to environment-friendly rice production. It was found that both desalinated-dried jellyfish and rice bran effectively controlled rice weeds when mixed in the soil before the transplanting.The grain yields of desalinated-dried jellyfish treatments were consistently higher than the corresponding rice bran treatments. The rice yield from the desalinated-dried jellyfish treatments were comparable to the chemical fertilizer treatment.
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