15,199 research outputs found
Viscosity of gauge theory plasma with a chemical potential from AdS/CFT correspondence
We compute the strong coupling limit of the shear viscosity for the N=4
super-Yang-Mill theory with a chemical potential. We use the five-dimensional
Reissner-Nordstrom-anti-deSitter black hole, so the chemical potential is the
one for the R-charges U(1)_R^3. We compute the quasinormal frequencies of the
gravitational and electromagnetic vector perturbations in the background
numerically. This enables one to explicitly locate the diffusion pole for the
shear viscosity. The ratio of the shear viscosity eta to the entropy density s
is eta/s=1/(4pi) within numerical errors, which is the same result as the one
without chemical potential.Comment: 11 pages, 5 figures, ReVTeX4; v2: minor improvements; v3:
explanations added and improved; v4: version to appear in PR
Robust and Scalable Scheme to Generate Large-Scale Entanglement Webs
We propose a robust and scalable scheme to generate an -qubit state
among separated quantum nodes (cavity-QED systems) by using linear optics and
postselections. The present scheme inherits the robustness of the Barrett-Kok
scheme [Phys. Rev. A {\bf 71}, 060310(R) (2005)]. The scalability is also
ensured in the sense that an arbitrarily large -qubit state can be
generated with a quasi-polynomial overhead . The
process to breed the states, which we introduce to achieve the scalability,
is quite simple and efficient, and can be applied for other physical systems.Comment: 5 pages, 3 figure
Gas Enrichment at Liquid-Wall Interfaces
Molecular dynamics simulations of Lennard-Jones systems are performed to
study the effects of dissolved gas on liquid-wall and liquid-gas interfaces.
Gas enrichment at walls is observed which for hydrophobic walls can exceed more
than two orders of magnitude when compared to the gas density in the bulk
liquid. As a consequence, the liquid structure close to the wall is
considerably modified, leading to an enhanced wall slip. At liquid-gas
interfaces gas enrichment is found which reduces the surface tension.Comment: main changes compared to version 1: flow simulations are included as
well as different types of gase
Radiation from an accelerated quark via AdS/CFT
In this paper we investigate radiation by an accelerated quark in a strongly
coupled gauge theory via AdS/CFT correspondence. According to AdS/CFT
dictionary, we can read off energy density or energy flux of the radiation from
asymptotic gravitational field in AdS bulk sourced by an accelerated string
trailing behind the quark. In the case of an oscillating quark with frequency
, we show that the time averaged energy density is asymptotically
isotropic and it falls off as with
distance from the source. In a toy model of a scattered quark by an
external field, we simply estimate Poynting vector by the bremsstrahlung
radiation and show that the energy flux is anisotropic outgoing radiation.
Based on these investigations, we discuss the properties of strongly coupled
gauge theory radiation in comparison with electromagnetic radiation.Comment: 16 pages, no figures, accepted for publication in Phys. Rev.
Nebular Spectra of SN 1998bw Revisited: Detailed Study by One and Two Dimensional Models
Refined one- and two-dimensional models for the nebular spectra of the
hyper-energetic Type Ic supernova (SN) 1998bw, associated with the gamma-ray
burst GRB980425, from 125 to 376 days after B-band maximum are presented. One
dimensional, spherically symmetric spectrum synthesis calculations show that
reproducing features in the observed spectra, i.e., the sharply peaked [OI]
6300\AA doublet and MgI] 4570\AA emission, and the broad [FeII] blend around
5200\AA, requires the existence of a high-density O-rich core expanding at low
velocities (\lsim 8,000 km s) and of Fe-rich material moving faster
than the O-rich material. Synthetic spectra at late phases from aspherical
(bipolar) explosion models are also computed with a two-dimensional spectrum
synthesis code. The above features are naturally explained by the aspherical
model if the explosion is viewed from a direction close to the axis of symmetry
(), since the aspherical model yields a high-density O-rich
region confined along the equatorial axis. By examining a large parameter space
(in energy and mass), our best model gives following physical quantities: the
kinetic energy ergs \gsim 8 - 12 and the
main-sequence mass of the progenitor star M_{\rm ms} \gsim 30 - 35 \Msun. The
temporal spectral evolution of SN 1998bw also indicates mixing among Fe-, O-,
and C-rich regions, and highly clumpy structure.Comment: 38 pages, 22 figures. ApJ, 640 (01 April 2006 issue), in pres
Exact Analysis of ESR Shift in the Spin-1/2 Heisenberg Antiferromagnetic Chain
A systematic perturbation theory is developed for the ESR shift and is
applied to the spin-1/2 Heisenberg chain. Using the Bethe ansatz technique, we
exactly analyze the resonance shift in the first order of perturbative
expansion with respect to an anisotropic exchange interaction. Exact result for
the whole range of temperature and magnetic field, as well as asymptotic
behavior in the low-temperature limit are presented. The obtained g-shift
strongly depends on magnetic fields at low temperature, showing a significant
deviation from the previous classical result.Comment: 4 pages, 3 figures,to be published in Phys. Rev. Let
Efeito da mistura de lodo celulósico com cinza de biomassa de madeira no desenvolvimento de Pinus taeda L.
Editores técnicos: Marcílio José Thomazini, Elenice Fritzsons, Patrícia Raquel Silva, Guilherme Schnell e Schuhli, Denise Jeton Cardoso, Luziane Franciscon. EVINCI. Resumos
Collision of Domain Walls and Reheating of the Brane Universe
We study a particle production at the collision of two domain walls in
5-dimensional Minkowski spacetime. This may provide the reheating mechanism of
an ekpyrotic (or cyclic) brane universe, in which two BPS branes collide and
evolve into a hot big bang universe. We evaluate a production rate of particles
confined to the domain wall. The energy density of created particles is given
as where is a coupling
constant of particles to a domain-wall scalar field, is the number of
bounces at the collision and is a fundamental mass scale of the domain
wall. It does not depend on the width of the domain wall, although the
typical energy scale of created particles is given by . The
reheating temperature is evaluated as . In order to have the baryogenesis at the electro-weak energy scale,
the fundamental mass scale is constrained as m_\eta \gsim 1.1\times 10^7 GeV
for .Comment: 10 pages, 12 figure
The effect of electromechanical coupling on the strain in AlGaN/GaN heterojunction field effect transistors
The strain in AlGaN/GaN heterojunction field-effect transistors (HFETs) is
examined theoretically in the context of the fully-coupled equation of state
for piezoelectric materials. Using a simple analytical model, it is shown that,
in the absence of a two-dimensional electron gas (2DEG), the out-of-plane
strain obtained without electromechanical coupling is in error by about 30% for
an Al fraction of 0.3. This result has consequences for the calculation of
quantities that depend directly on the strain tensor. These quantities include
the eigenstates and electrostatic potential in AlGaN/GaN heterostructures. It
is shown that for an HFET, the electromechanical coupling is screened by the
2DEG. Results for the electromechanical model, including the 2DEG, indicate
that the standard (decoupled) strain model is a reasonable approximation for
HFET calculataions. The analytical results are supported by a self-consistent
Schr\"odinger-Poisson calculation that includes the fully-coupled equation of
state together with the charge-balance equation.Comment: 6 figures, revte
On two pieces of folklore in the AdS/CFT duality
In the AdS/CFT duality, it is often said that a local symmetry in a bulk
theory corresponds to a global symmetry in the corresponding boundary theory,
but the global symmetry can become local when one couples with an external
source. As a result, the GKP-Witten relation gives a response function instead
of a Green function. We explore this point in details using the example of
holographic superconductors. We point out that these points play a crucial role
to interpret the holographic London equation properly.Comment: 11 pages, ReVTeX4.1; v2: added discussio
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