235 research outputs found
Wilson-t'Hooft Loops in Finite-Temperature Non-commutative Dipole Field Theory from Dual Supergravity
We first study the temporal Wilson loop in the finite-temperature
non-commutative dipole field theory from the string/gauge correspondence. The
associated dual supergravity background is constructed from the near-horizon
geometry of near-extremal D-branes, after applying T-duality and smeared twist.
We investigate the string configuration therein and find that while the
temperature produces a maximum distance in the interquark distance
the dipole in there could produce a minimum distance . The quark
boundary pair therefore could be found only if their distance is between
and . We also show that, beyond a critical temperature the
quark pair becomes totally free due to screening by thermal bath. We next study
the spatial Wilson loop and find the confining nature in the zero temperature
3D and 4D non-supersymmetry dipole gauge theory. The string tension of the
linear confinement potential is obtained and found to be a decreasing function
of the dipole field. We also investigate the associated t'Hooft loop and
determine the corresponding monopole anti-monopole potential. The conventional
screening of magnetic charge which indicates the confinement of the electric
charge is replaced by a strong repulsive however. Finally, we show that the
dual string which is rotating along the dipole deformed will behave as a
static one without dipole field, which has no minimum distance and has larger
energy than a static one with dipole field. We discuss the phase transition
between these string solutions.Comment: Latex, 22 pages, 8 figures, add several comment
Spin Chain with Magnetic Field and Spinning String in Magnetic Field Background
We analyze the fast-moving string in the magnetic Melvin field background and
find that the associated effective Lagrangian of string sigma model describes
the spin chain model with external magnetic field. The spin vector in the spin
chain has been properly deformed and is living on the deformed two-sphere or
deformed two-dimensional hyperboloid, depending on the direction around which
the string is spinning. We describe in detail the characters of spin
deformation and, in particular, see that this is a general property for a
string moving in a class of deformed background.Comment: Latex 10 pages, add a figure and a section, change titl
Spinning String and Giant Graviton in Electric/Magnetic Field Deformed
We apply the transformation of mixing azimuthal and internal coordinate or
mixing time and internal coordinate to the 11D M-theory with a stack of
M2-branes M2-branes, then, through the mechanism of Kaluza-Klein
reduction and a series of the T duality we obtain the corresponding background
of a stack of D1-branes D5-branes which, in the near-horizon limit,
becomes the magnetic or electric Melvin field deformed . We find the giant graviton solution in the deformed spacetime and see
that the configuration whose angular momentum is within a finite region could
has a fixed size and become more stable than the point-like graviton, in
contrast to the undeformed giant graviton which only exists when its angular
momentum is a specific value and could have arbitrary size. We discuss in
detail the properties of how the electric/magnetic Melvin field will affect the
size of the giant gravitons. We also adopt an ansatz to find the classical
string solutions which are rotating in the deformed with an angular
momentum in the rotation plane. The spinning string and giant graviton
solutions we obtained show that the external magnetic/electric flux will
increase the solution energy. Therefore, from the AdS/CFT point of view, the
corrections of the anomalous dimensions of operators in the dual field theory
will be positive. Finally, we also see that the spinning string and giant
graviton in the near-horizon spacetime of Melvin field deformed D5-branes
background have the similar properties as those in the deformed .Comment: Latex 21 pages, slightly detail calculation
Semiclassical Strings in Electric and Magnetic Fields Deformed Spacetimes
We first apply the transformation of mixing azimuthal and internal coordinate
or mixing time and internal coordinate to the 11D M-theory with a stack N
M2-branes to find the spacetime of a stack of N D2-branes with magnetic or
electric flux in 10 D IIA string theory, after the Kaluza-Klein reduction. We
then perform the T duality to the spacetime to find the background of a stack
of N D3-branes with magnetic or electric flux. In the near-horizon limit the
background becomes the magnetic or electric field deformed .
We adopt an ansatz to find the classical string solution which is rotating in
the deformed with three angular momenta in the three rotation planes. The
relations between the classical string energy and its angular momenta are found
and results show that the external magnetic and electric fluxes will increase
the string energy. Therefore, from the AdS/CFT point of view, the corrections
of the anomalous dimensions of operators in the dual SYM theory will be
positive. We also investigate the small fluctuations in these solutions and
discuss the effects of magnetic and electric fields on the stability of these
classical rotating string solutions. Finally, we find the possible solutions of
string pulsating on the deformed spacetimes and show that the corrections to
the anomalous dimensions of operators in the dual SYM theory are non-negative.Comment: Latex 18 pages, correct sec. 3.
Thermal Instability of Giant Graviton in Matrix Model on PP-wave Background
The thermal instability of the giant graviton is investigated within the BMN
matrix model. We calculate the one-loop thermal correction of the quantum
fluctuation around the trivial vacuum and giant graviton respectively. From the
exact formula of the free energy we see that at low temperature the giant
graviton is unstable and will dissolve into vacuum fluctuation. However, at
sufficient high temperature the trivial vacuum fluctuation will condense to
form the giant graviton configuration. The transition temperature of the giant
graviton is determined in our calculation.Comment: Latex, 8 pages, typos corrected, mention the elliptic deformation of
giant gravito
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
Tachyon Tube on non BPS D-branes
We report our searches for a single tubular tachyonic solution of regular
profile on unstable non BPS D3-branes. We first show that some extended
Dirac-Born-Infeld tachyon actions in which new contributions are added to avoid
the Derrick's no-go theorem still could not have a single regular tube
solution. Next we use the Minahan-Zwiebach tachyon action to find the regular
tube solutions with circular or elliptic cross section. With a critical
electric field, the energy of the tube comes entirely from the D0 and strings,
while the energy associated to the tubular D2-brane tension is vanishing. We
also show that fluctuation spectrum around the tube solution does not contain
tachyonic mode. The results are consistent with the identification of the
tubular configuration as a BPS D2-brane.Comment: Latex 18 page
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
Cohesive-zone modelling of the deformation and fracture of spot-welded joints
The deformation and failure of spot-welded joints have been successfully modelled using a cohesive-zone model for fracture. This has been accomplished by implementing a user-defined, three-dimensional, cohesive-zone element within a commercial finite-element package. The model requires two material parameters for each mode of deformation. Results show that the material parameters from this type of approach are transferable for identical spot welds in different geometries where a single parameter (such as maximum stress) is not. The approach has been demonstrated using a model system consisting of spot-welded joints made from 5754 aluminium sheets. The techniques for determining the cohesive fracture parameters for both nugget fracture and nugget pullout are described in this paper. It has been demonstrated that once the appropriate cohesive parameters for a weld are determined, quantitative predictions can be developed for the strengths, deformations and failure mechanisms of different geometries with nominally identical welds.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73187/1/j.1460-2695.2005.00919.x.pd
The lipoprotein lipase gene in combined hyperlipidemia: evidence of a protective allele depletion
BACKGROUND: Lipoprotein Lipase (LPL), a key enzyme in lipid metabolism, catalyzes the hydrolysis of triglycerides (TG) from TG-rich lipoproteins, and serves a bridging function that enhances the cellular uptake of lipoproteins. Abnormalities in LPL function are associated with pathophysiological conditions, including familial combined hyperlipidemia (FCH). Whereas two LPL susceptibility alleles were found to co-segregate in a few FCH kindred, a role for common, protective alleles remains unexplored. The LPL Ser447Stop (S447X) allele is associated with anti-atherogenic lipid profiles and a modest reduction in risk for coronary disease. We hypothesize that significant depletion of the 447X allele exists in combined hyperlipidemia cases versus controls. A case-control design was employed. The polymorphism was assessed by restriction assay in 212 cases and 161 controls. Genotypic, allelic, and phenotypic associations were examined. RESULTS: We found evidence of significant allelic (447X(control): 0.130 vs. 447X(case): 0.031, χ(2 )= 29.085; 1df; p < 0.001) and genotypic association (SS: 0.745 vs. 0.939, and SX+XX: 0.255 vs. 0.061) in controls and cases, respectively (χ(2 )= 26.09; 1df; p < 0.001). In cases, depletion of the 447X allele is associated with a significant elevation in very-low-density lipoprotein cholesterol (VLDL-C, p = 0.045). Consonant with previous studies of this polymorphism, regression models predict that carriers of the 447X allele displayed significantly lower TG, low-density lipoprotein cholesterol (LDL-C) and TG/high-density lipoprotein cholesterol (HDL-C) ratio. CONCLUSION: These findings suggest a role for the S447X polymorphism in combined hyperlipidemia and demonstrate the importance of evaluating both susceptibility and protective genetic risk factors
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