140 research outputs found
Condensation of Tubular D2-branes in Magnetic Field Background
It is known that in the Minkowski vacuum a bunch of IIA superstrings with
D0-branes can be blown-up to a supersymmetric tubular D2-brane, which is
supported against collapse by the angular momentum generated by crossed
electric and magnetic Born-Infeld (BI) fields. In this paper we show how the
multiple, smaller tubes with relative angular momentum could condense to a
single, larger tube to stabilize the system. Such a phenomena could also be
shown in the systems under the Melvin magnetic tube or uniform magnetic field
background. However, depending on the magnitude of field strength, a tube in
the uniform magnetic field background may split into multiple, smaller tubes
with relative angular momentum to stabilize the system.Comment: Latex 10 pages, mention the dynamical joining of the tubes, modify
figure
Hawking Radiation of a Quantum Black Hole in an Inflationary Universe
The quantum stress-energy tensor of a massless scalar field propagating in
the two-dimensional Vaidya-de Sitter metric, which describes a classical model
spacetime for a dynamical evaporating black hole in an inflationary universe,
is analyzed. We present a possible way to obtain the Hawking radiation terms
for the model with arbitrary functions of mass. It is used to see how the
expansion of universe will affect the dynamical process of black hole
evaporation. The results show that the cosmological inflation has an
inclination to depress the black hole evaporation. However, if the cosmological
constant is sufficiently large then the back-reaction effect has the
inclination to increase the black hole evaporation. We also present a simple
method to show that it will always produce a divergent flux of outgoing
radiation along the Cauchy horizon where the curvature is a finite value. This
means that the Hawking radiation will be very large in there and shall modify
the classical spacetime drastically. Therefore the black hole evaporation
cannot be discussed self-consistently on the classical Vaidya-type spacetime.
Our method can also be applied to analyze the quantum stress-energy tensor in
the more general Vaidya-type spacetimes.Comment: Proper boundary will lead to anti-evaporation of schwarzschild-de
Sitter black holes, as corrected in Class. Quantum Grav. 11 (1994) 28
Microcanonical statistics of black holes and bootstrap condition
The microcanonical statistics of the Schwarzschild black holes as well as the
Reissner-Nordstrm black holes are analyzed. In both cases we set
up the inequalities in the microcanonical density of states.
These are then used to show that the most probable configuration in the gases
of black holes is that one black hole acquires all of the mass and all of the
charge at high energy limit. Thus the black holes obey the statistical
bootstrap condition and, in contrast to the other investigation, we see that
U(1) charge does not break the bootstrap property.Comment: 16 pages. late
Holographic Description of Glueball and Baryon in Noncommutative Dipole Gauge Theory
We study the glueball spectrum in the supersymmetric and non-supersymmetric
4D non-commutative dipole gauge theory from the holographic description. We
adopt the semiclassical WKB approximation to solve the dilaton and
antisymmetric tensor field equations on the dual supergravity backgrounds to
find the analytic formula of the spectrum of and glueballs,
respectively. In the supersymmetric theory we see that the dipole length plays
the intrinsic scale which reflects the discrete spectrum therein. In the
non-supersymmetric theory, the temperature (or the radius of compactification)
in there will now play the intrinsic scale and we see that the dipole has an
effect to produce attractive force between the gluons within the glueball. We
also study the confining force between the quarks within the baryon via strings
that hang into the dipole deformed AdS geometry and see that the dipole could
also produce an attractive force between the quarks. In particular, we find
that the baryon has two phases in which a big baryon is dual to the static
string while a small baryon is described by a moving dual string .Comment: Latex 18 page
High-Temperature Effective Potential of Noncommutative Scalar Field Theory: Reduction of Degree of Freedom by Noncommutativity
The renormalization of effective potentials for the noncommutative scalar
field theory at high temperature are investigated to the two-loop
approximation. The Feynman diagrams in evaluating the effective potential may
be classified into two types: the planar diagrams and nonplanar diagrams. The
nonplanar diagrams, which depend on the parameter of noncommutativity, do not
appear in the one-loop potential. Despite their appearance in the two-loop
level, they do not have an inclination to restore the symmetry breaking in the
tree level, in contrast to the planar diagrams. This phenomenon is explained as
a consequence of the drastic reduction of the degrees of freedom in the
nonplanar diagrams when the thermal wavelength is smaller than the
noncommutativity scale. Our results show that the nonplanar two-loop
contribution to the effective potential can be neglected in comparsion with
that from the planar diagrams.Comment: Latex, 17 pages, change the conclusion, improve the Englis
Chronology Protection in Generalized Godel Spacetime
The effective action of a free scalar field propagating in the generalized
Godel spacetime is evaluated by the zeta-function regularization method. From
the result we show that the renormalized stress energy tensor may be divergent
at the chronology horizon. This gives a support to the chronology protection
conjecture.Comment: Latex 6 pages, typos correcte
Rewritable nanoscale oxide photodetector
Nanophotonic devices seek to generate, guide, and/or detect light using
structures whose nanoscale dimensions are closely tied to their functionality.
Semiconducting nanowires, grown with tailored optoelectronic properties, have
been successfully placed into devices for a variety of applications. However,
the integration of photonic nanostructures with electronic circuitry has always
been one of the most challenging aspects of device development. Here we report
the development of rewritable nanoscale photodetectors created at the interface
between LaAlO3 and SrTiO3. Nanowire junctions with characteristic dimensions
2-3 nm are created using a reversible AFM writing technique. These nanoscale
devices exhibit a remarkably high gain for their size, in part because of the
large electric fields produced in the gap region. The photoconductive response
is gate-tunable and spans the visible-to-near-infrared regime. The ability to
integrate rewritable nanoscale photodetectors with nanowires and transistors in
a single materials platform foreshadows new families of integrated
optoelectronic devices and applications.Comment: 5 pages, 5 figures. Supplementary Information 7 pages, 9 figure
Multi-spin String Solutions in Magnetic-flux Deformed Spacetime
We perform the dimensional reduction of the spacetime of a stack of N
D3-branes by the ``twist'' identification of a circle to obtain a new Melvin
background. In the near-horizon limit the background becomes the magnetic-flux
deformed or spacetime. After analyzing
the classical closed string solutions with several angular momenta in different
directions of the deformed spacetimes we obtain two string solutions. The first
solution describes a circular closed string located at a fixed value of
deformed radius while rotating simultaneously in two planes in deformed
with equal spins . The second solution describes a string rotating
in deformed with two equal angular momenta in the two rotation
planes. We investigate the small fluctuations therein and show that the
magnetic fluxes have inclination to improve the stability of these classical
string solutions.Comment: Latex 15 pages, add a little comment in discussio
The conserved 5′ apical hairpin stem loops of bamboo mosaic virus and its satellite RNA contribute to replication competence
Satellite RNAs associated with Bamboo mosaic virus (satBaMVs) depend on BaMV for replication and encapsidation. Certain satBaMVs isolated from natural fields significantly interfere with BaMV replication. The 5′ apical hairpin stem loop (AHSL) of satBaMV is the major determinant in interference with BaMV replication. In this study, by in vivo competition assay, we revealed that the sequence and structure of AHSL, along with specific nucleotides (C60 and C83) required for interference with BaMV replication, are also involved in replication competition among satBaMV variants. Moreover, all of the 5′ ends of natural BaMV isolates contain the similar AHSLs having conserved nucleotides (C64 and C86) with those of interfering satBaMVs, suggesting their co-evolution. Mutational analyses revealed that C86 was essential for BaMV replication, and that replacement of C64 with U reduced replication efficiency. The non-interfering satBaMV interfered with BaMV replication with the BaMV-C64U mutant as helper. These findings suggest that two cytosines at the equivalent positions in the AHSLs of BaMV and satBaMV play a crucial role in replication competence. The downregulation level, which is dependent upon the molar ratio of interfering satBaMV to BaMV, implies that there is competition for limited replication machinery
- …