2,157 research outputs found
Relativistic superfluidity and vorticity from the nonlinear Klein-Gordon equation
We investigate superfluidity, and the mechanism for creation of quantized vortices, in the relativistic regime.The general framework is a nonlinear Klein-Gordon equation in curved spacetime for a complex scalar field, whose phase dynamics gives rise to superfluidity. The mechanisms discussed are local inertial forces (Coriolis and centrifugal), and current-current interaction with an external source. The primary application is to cosmology, but we also discuss the reduction to the non-relativistic nonlinear Schr¨odinger equation, which is widely used in describing superfluidity and vorticity in liquid helium and cold-trapped atomic gase
Phantom Field with O(N) Symmetry in Exponential Potential
In this paper, we study the phase space of phantom model with O(\emph{N})
symmetry in exponential potential. Different from the model without O(\emph{N})
symmetry, the introduction of the symmetry leads to a lower bound on the
equation of state for the existence of stable phantom dominated attractor
phase. The reconstruction relation between the potential of O(\textit{N})
phantom system and red shift has been derived.Comment: 5 pages, 3 figures, replaced with the version to appear on Phys. Rev.
The accelerated scaling attractor solution of the interacting agegraphic dark energy in Brans-Dicke theory
We investigate the interacting agegraphic dark energy in Brans-Dicke theory
and introduce a new series general forms of dark sector coupling. As examples,
we select three cases involving a linear interaction form (Model I) and two
nonlinear interaction form (Model II and Model III). Our conclusions show that
the accelerated scaling attractor solutions do exist in these models. We also
find that these interacting agegraphic dark energy modes are consistent with
the observational data. The difference in these models is that nonlinear
interaction forms give more approached evolution to the standard CDM
model than the linear one. Our work implies that the nonlinear interaction
forms should be payed more attention.Comment: 9 pages, 10 figures, accepted in Eur. Phys. J.
Parameterization and Reconstruction of Quasi Static Universe
We study a possibility of the fate of universe, in which there is neither the
rip singularity, which results in the disintegration of bound systems, nor the
endless expansion, instead the universe will be quasi static. We discuss the
parameterization of the corresponding evolution and the reconstruction of the
scalar field model. We find, with the parameterization consistent with the
current observation, that the current universe might arrive at a quasi static
phase after less than 20Gyr.Comment: minor changes and Refs. added, publish in EPJ
An efficient method for the incompressible Navier-Stokes equations on irregular domains with no-slip boundary conditions, high order up to the boundary
Common efficient schemes for the incompressible Navier-Stokes equations, such
as projection or fractional step methods, have limited temporal accuracy as a
result of matrix splitting errors, or introduce errors near the domain
boundaries (which destroy uniform convergence to the solution). In this paper
we recast the incompressible (constant density) Navier-Stokes equations (with
the velocity prescribed at the boundary) as an equivalent system, for the
primary variables velocity and pressure. We do this in the usual way away from
the boundaries, by replacing the incompressibility condition on the velocity by
a Poisson equation for the pressure. The key difference from the usual
approaches occurs at the boundaries, where we use boundary conditions that
unequivocally allow the pressure to be recovered from knowledge of the velocity
at any fixed time. This avoids the common difficulty of an, apparently,
over-determined Poisson problem. Since in this alternative formulation the
pressure can be accurately and efficiently recovered from the velocity, the
recast equations are ideal for numerical marching methods. The new system can
be discretized using a variety of methods, in principle to any desired order of
accuracy. In this work we illustrate the approach with a 2-D second order
finite difference scheme on a Cartesian grid, and devise an algorithm to solve
the equations on domains with curved (non-conforming) boundaries, including a
case with a non-trivial topology (a circular obstruction inside the domain).
This algorithm achieves second order accuracy (in L-infinity), for both the
velocity and the pressure. The scheme has a natural extension to 3-D.Comment: 50 pages, 14 figure
Quasi-Periodic Releases of Streamer Blobs and Velocity Variability of the Slow Solar Wind near the Sun
We search for persistent and quasi-periodic release events of streamer blobs
during 2007 with the Large Angle Spectrometric Coronagraph on the \textit{Solar
and Heliospheric Observatory} and assess the velocity of the slow solar wind
along the plasma sheet above the corresponding streamer by measuring the
dynamic parameters of blobs. We find 10 quasi-periodic release events of
streamer blobs lasting for three to four days. In each day of these events, we
observe three-five blobs. The results are in line with previous studies using
data observed near the last solar minimum. Using the measured blob velocity as
a proxy for that of the mean flow, we suggest that the velocity of the
background slow solar wind near the Sun can vary significantly within a few
hours. This provides an observational manifestation of the large velocity
variability of the slow solar wind near the Sun.Comment: 14 pages, 5 figures, accepted by Soalr Physic
An example of localized D-branes solution on PP-wave backgrounds
In this note we provide an explicit example of type IIB supersymmetric
D3-branes solution on a pp-wave like background, consisting in the product of
an eight-dimensional pp-wave times a two-dimensional flat space. An interesting
property of our solution is the fully localization of the D3-branes (i.e. the
solution depends on all the transverse coordinates). Then we show the
generalization to other Dp-branes and to the D1/D5 system.Comment: 14 pages, 1 table; v2. references adde
Multiple CDM cosmology with string landscape features and future singularities
Multiple CDM cosmology is studied in a way that is formally a
classical analog of the Casimir effect. Such cosmology corresponds to a
time-dependent dark fluid model or, alternatively, to its scalar field
presentation, and it motivated by the string landscape picture. The future
evolution of the several dark energy models constructed within the scheme is
carefully investigated. It turns out to be almost always possible to choose the
parameters in the models so that they match the most recent and accurate
astronomical values. To this end, several universes are presented which mimick
(multiple) CDM cosmology but exhibit Little Rip, asymptotically de
Sitter, or Type I, II, III, and IV finite-time singularity behavior in the far
future, with disintegration of all bound objects in the cases of Big Rip,
Little Rip and Pseudo-Rip cosmologies.Comment: LaTeX 11 pages, 10 figure
Immunohistochemical detection of somatostatin receptor subtypes sst1 and sst2A in human somatostatin receptor positive tumors
Although in situ hybridization has been used to examine the distribution
of messenger RNA for somatostatin receptor subtypes (sst) in human tumors,
the cellular localization of sst1 and sst2A receptors has not been
reported. In this study, we describe the cellular localization of human
sst1 and sst2A receptor proteins in both cryostat- and paraffin-embedded
sections of 25 human tumor tissues using two recently developed polyclonal
antibodies. Six somatostatin (SS) receptor (SSR) positive tumors (two
gastrinomas, three carcinoids, one pheochromocytoma) and one SSR negative
tumor (renal cell carcinoma), selected by positive and negative SSR
autoradiography, respectively, were studied by both immunohistochemistry
and Western blot analysis. The six SSR positive tumors expressed sst2A,
while 4 of 5 expressed sst1 as well. The SSR negative tumor did not
express either sst1 or sst2A. Western blot analysis of wheat germ
agglutinin purified membrane proteins confirmed the presence of the sst1
and sst2A glycosylated receptors. The paraffin-embedded sections gave best
information with respect to the subcellular localization. Sst1
immunoreactivity was observed both on the membrane and in the cytoplasm,
while sst2A showed predominantly membrane-associated immunoreactivity.
This subcellular distribution of sst1 or sst2A receptors was confirmed in
paraffin-embedded sections of 8 additional intestinal carcinoids, 5
gastrinomas and 5 pheochromocytomas. Sst1 receptors were detected in 7 out
of 8 carcinoids, in all gastrinomas, and in 4 out of 5 pheochromocytomas,
while 6 out of 8 carcinoids, all gastrinomas, and 3 out of 5
pheochromocytomas expressed sst2A receptors. In conclusion, sst1 and sst2A
receptors show a differential subcellular localization in human SSR
positive tumors. The use of SSR subtype selective antibodies to detect the
subcellular distribution of SSR subtypes in individual tumor cells is an
important step forward to understand more about the pathophysiological
role of the different SSR subtypes in human tumors
Schwarzschild black hole surrounded by quintessence: Null geodesics
We have studied the null geodesics of the Schwarzschild black hole surrounded
by quintessence matter. Quintessence matter is a candidate for dark energy.
Here, we have done a detailed analysis of the geodesics and exact solutions are
presented in terms of Jacobi-elliptic integrals for all possible energy and
angular momentum of the photons. The circular orbits of the photons are studied
in detail. As an application of the null geodesics, the angle of deflection of
the photons are computed.Comment: 25 pages, 20 figures. typos corrected and some of the notation
change
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