41 research outputs found
Holographic model with a NS-NS field
We consider a holographic model constructed through using the D4/D8- brane configuration with a background field. We study some properties of
the effective field theory in this intersecting brane construction, and
calculate the effects of this NS-NS background field on some underlying
dynamics. We also discuss some other general brane configurations.Comment: 36 pages, some figures are revised, and to appear in pr
The Dropping of In-Medium Hadron Mass in Holographic QCD
We study the baryon density dependence of the vector meson spectrum using the
D4/D6 system together with the compact D4 baryon vertex. We find that the
vector meson mass decreases almost linearly in density at low density for small
quark mass, but saturates to a finite non-zero value for large density. We also
compute the density dependence of the mass and the
velocity. We find that in medium, our model is consistent with the GMOR
relation up to a few times the normal nuclear density. We compare our hQCD
predictions with predictions made based on hidden local gauge theory that is
constructed to model QCD.Comment: 20 pages, 7 figure
Perturbation theory of the space-time non-commutative real scalar field theories
The perturbative framework of the space-time non-commutative real scalar
field theory is formulated, based on the unitary S-matrix. Unitarity of the
S-matrix is explicitly checked order by order using the Heisenberg picture of
Lagrangian formalism of the second quantized operators, with the emphasis of
the so-called minimal realization of the time-ordering step function and of the
importance of the -time ordering. The Feynman rule is established and is
presented using scalar field theory. It is shown that the divergence
structure of space-time non-commutative theory is the same as the one of
space-space non-commutative theory, while there is no UV-IR mixing problem in
this space-time non-commutative theory.Comment: Latex 26 pages, notations modified, add reference
Seoul National University Bright Quasar Survey in Optical (SNUQSO). II. Discovery of 40 Bright Quasars Near the Galactic Plane
We report the discovery of 40 bright quasars and active galactic nuclei
(AGNs) at low Galactic latitude (b<20deg). The low Galactic latitude region has
been considered a place to avoid when searching for extragalactic sources,
because of the high Galactic extinction, as well as a large number of stars
contaminating the sample selection. Bright quasars (R<~17) suffer more from
such difficulties because they look like bright stars, which are numerous at
low b, yet their surface number density is very low. In order to find quasars
in this region of the sky less explored for extragalactic sources, we have
started a survey of low Galactic latitude bright quasars as a part of the Seoul
National University Quasar Survey in Optical (SNUQSO). Quasar candidates have
been selected from radio and near-infrared (NIR) data. Out of 88 targets, we
identify 29 bright quasars/AGNs around the antigalactic center, and 11 bright
quasars/AGNs in the outskirts of the Galactic center, from two observing runs
in 2006 at the Bohyunsan Optical Astronomical Observatory (BOAO) in Korea. Our
finding demonstrates that quasars/AGNs can be discovered effectively, even at
low Galactic latitude, using multiwavelength data.Comment: 16 pages, 3 figure
Effects of transcutaneous electrical nerve stimulation on myocardial protection in patients undergoing aortic valve replacement: a randomized clinical trial
Abstract
Background
Cardiopulmonary bypass-related myocardial ischemia-reperfusion injury is a major contributor to postoperative morbidity. Although transcutaneous electrical nerve stimulation (TENS) has been found to have cardioprotective effects in animal studies and healthy volunteers, its effects on cardiac surgery under cardiopulmonary bypass patients have not been evaluated. We investigated the effects of TENS on myocardial protection in patients undergoing aortic valve replacement surgery using cardiopulmonary bypass.
Methods
Thirty patients were randomized to receive TENS or sham in three different anesthetic states – pre-anesthesia, sevoflurane, or propofol (each n = 5). TENS was applied with a pulse width of 385 μs and a frequency of 10 Hz using two surface electrodes at the upper arm for 30 min. Sham treatment was provided without stimulation. The primary outcome was the difference in myocardial infarct size following ischemia-reperfusion injury in rat hearts perfused with pre- and post-TENS plasma dialysate obtained from the patients using Langendorff perfusion system. The cardioprotective effects of TENS were determined by assessing reduction in infarct size following treatment.
Results
There were no differences in myocardial infarct size between pre- and post-treatment in any group (41.4 ± 4.3% vs. 36.7 ± 5.3%, 39.8 ± 7.3% vs. 27.8 ± 12.0%, and 41.6 ± 2.2% vs. 37.8 ± 7.6%; p = 0.080, 0.152, and 0.353 in the pre-anesthesia, sevoflurane, and propofol groups, respectively).
Conclusions
In our study, TENS did not show a cardioprotective effect in patients undergoing aortic valve replacement surgery.
Trial registration
This study was registered at clinicaltrials.gov (
NCT03859115
, on March 1, 2019)
Holographic Hadrons in a Confining Finite Density Medium
We study a sector of the hadron spectrum in the presence of finite baryon
density. We use a non-supersymmetric gravity dual to a confining guage theory
which exhibits a running dilaton. The interaction of mesons with the finite
density medium is encoded in the dual theory by a force balancing between
flavor D7-branes and a baryon vertex provided by a wrapped D5-brane. When the
current quark mass m_q is sufficiently large, the meson mass reduces,
exhibiting an interesting spectral flow as we increase the baryon density while
it has a more complicated behaviour for very small m_q.Comment: 34 pages, 20 figures, errors for some figures are fixe
Symmetry energy of dense matter in holographic QCD
We study the nuclear symmetry energy of dense matter using holographic QCD.
To this end, we consider two flavor branes with equal quark masses in a
D4/D6/D6 model. We find that at all densities the symmetry energy monotonically
increases. At small densities, it exhibits a power law behavior with the
density, .Comment: 9 pages, 3 figure
Nuclear matter to strange matter transition in holographic QCD
We construct a simple holographic QCD model to study nuclear matter to
strange matter transition. The interaction of dense medium and hadrons is taken
care of by imposing the force balancing condition for stable D4/D6/D6
configuration. By considering the intermediate and light flavor branes
interacting with baryon vertex homogeneously distributed along R^3 space and
requesting the energy minimization, we find that there is a well defined
transition density as a function of current quark mass. We also find that as
density goes up very high, intermediate (or heavy) and light quarks populate
equally as expected from the Pauli principle. In this sense, the effect of the
Pauli principle is realized as dynamics of D-branes.Comment: 13 pages, 14 figure
The Baryonic Phase in Holographic Descriptions of the QCD Phase Diagram
We study holographic models of the QCD temperature-chemical potential phase
diagram based on the D3/D7 system with chiral symmetry breaking. The baryonic
phase may be included through linked D5-D7 systems. In a previous analysis of a
model with a running gauge coupling a baryonic phase was shown to exist to
arbitrarily large chemical potential. Here we explore this phase in a more
generic phenomenological setting with a step function dilaton profile. The
change in dilaton generates a linear confining potential and opposes
the screening effect of temperature. We show that the persistence of the
baryonic phase depends on the step size and that QCD-like phase diagrams can be
described. The baryonic phase's existence is qualitatively linked to the
existence of confinement in Wilson loop computations in the background.Comment: 21 pages, 7 figure
Symmetry Energy and Universality classes of holographic QCD
We study nuclear symmetry energy of dense matter using holographic QCD. We
calculate it in a various holographic QCD models and show that the scaling
index of the symmetry energy in dense medium is almost invariant under the
smooth deformation of the metric as well as the embedding shape of the probe
brane. We find that the scaling index depends only on the dimensionality of the
branes and space-time. Therefore the scaling index of the symmetry energy
characterizes the universality classes of holographic QCD models. We suggest
that the scaling index might be also related to the non-fermi liquid behavior
of the interacting nucleons.Comment: 23 pages, 17 figure