4,954 research outputs found
FORS2/VLT survey of Milky Way globular clusters I. Description of the method for derivation of metal abundances in the optical and application to NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426 and Terzan 8
(abridged) We have observed almost 1/3 of the globular clusters in the Milky
Way, targeting distant and/or highly reddened objects, besides a few reference
clusters. A large sample of red giant stars was observed with FORS2@VLT/ESO at
R ~ 2,000. The method for derivation of stellar parameters is presented with
application to six reference clusters. We aim at deriving the stellar
parameters effective temperature, gravity, metallicity and alpha-element
enhancement, as well as radial velocity, for membership confirmation of
individual stars in each cluster. We analyse the spectra collected for the
reference globular clusters NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426 and
Terzan 8. They cover the full range of globular cluster metallicities, and are
located in the bulge, disc and halo. Full spectrum fitting techniques are
applied, by comparing each target spectrum with a stellar library in the
optical region at 4560-5860 A. We employed the library of observed spectra
MILES, and the synthetic library by Coelho et al. (2005). Validation of the
method is achieved through recovery of the known atmospheric parameters for 49
well-studied stars that cover a wide range in the parameter space. We adopted
as final stellar parameters (effective temperatures, gravities, metallicities)
the average of results using MILES and Coelho et al. libraries. We identified 4
member stars in NGC 6528, 13 in NGC 6553, 10 in M 71, 5 in NGC 6558, 5 in NGC
6426 and 12 in Terzan 8. Radial velocities, Teff, log(g), [Fe/H] and
alpha-element enhancements were derived. We derived abundances for NGC 6426
from spectroscopy for the first time. The method proved to be reliable for red
giant stars observed with resolution R ~ 2,000, yielding results compatible
with high-resolution spectroscopy. The derived alpha-element abundances show
[A/Fe] vs. [Fe/H] consistent with that of field stars at the same
metallicities.Comment: 22 pages, 21 figures, accepted for publication in A&
Massive Pions, Anomalies and Baryons in Holographic QCD
We consider a holographic model of QCD, obtained by a very simple
modification of the original construction, which describes at the same time the
pion mass, the QCD anomalies and the baryons as topological solitons. We study
in detail its phenomenological implications in both the mesonic and baryonic
sectors and compare with the observations.Comment: 31 pages, 2 figures; v2: Version published in Nucl. Phys.
Tests of Universality of Baryon Form Factors in Holographic QCD
We describe a new exact relation for large QCD for the long-distance
behavior of baryon form factors in the chiral limit, satisfied by all 4D
semi-classical chiral soliton models. We use this relation to test the
consistency of the structure of two different holographic models of baryons.Comment: 4 pages. Talk presented by MN at Light Cone 2009: Relativistic
Hadronic and Particle Physics, 8-13 Jul 2009, Sao Jose dos Campos, Brazi
Linear Confinement and AdS/QCD
In a theory with linear confinement, such as QCD, the masses squared m^2 of
mesons with high spin S or high radial excitation number n are expected, from
semiclassical arguments, to grow linearly with S and n. We show that this
behavior can be reproduced within a putative 5-dimensional theory
holographically dual to QCD (AdS/QCD). With the assumption that such a dual
theory exists and describes highly excited mesons as well, we show that
asymptotically linear m^2 spectrum translates into a strong constraint on the
INFRARED behavior of that theory. In the simplest model which obeys such a
constraint we find m^2 ~ (n+S).Comment: 14 pages, 1 figur
Centrifugal force induced by relativistically rotating spheroids and cylinders
Starting from the gravitational potential of a Newtonian spheroidal shell we
discuss electrically charged rotating prolate spheroidal shells in the Maxwell
theory. In particular we consider two confocal charged shells which rotate
oppositely in such a way that there is no magnetic field outside the outer
shell. In the Einstein theory we solve the Ernst equations in the region where
the long prolate spheroids are almost cylindrical; in equatorial regions the
exact Lewis "rotating cylindrical" solution is so derived by a limiting
procedure from a spatially bound system. In the second part we analyze two
cylindrical shells rotating in opposite directions in such a way that the
static Levi-Civita metric is produced outside and no angular momentum flux
escapes to infinity. The rotation of the local inertial frames in flat space
inside the inner cylinder is thus exhibited without any approximation or
interpretational difficulties within this model.
A test particle within the inner cylinder kept at rest with respect to axes
that do not rotate as seen from infinity experiences a centrifugal force.
Although the spacetime there is Minkowskian out to the inner cylinder
nevertheless that space has been induced to rotate, so relative to the local
inertial frame the particle is traversing a circular orbit.Comment: 12 pages, 2 figure
Presynaptic actions of 4-Aminopyridine and γ-aminobutyric acid on rat sympathetic ganglia in vitro
Responses to bath-applications of 4-aminopyridine (4-AP) and -aminobutyric acid (GABA) were recorded intracellularly from neurones in the rat isolated superior cervical ganglion.
4-aminopyridine (0.1–1.0 mmol/l) usually induced spontaneous action potentials and excitatory postsynaptic potentials (EPSPs), which were blocked by hexamethonium. Membrane potential was unchanged; spike duration was slightly increased. Vagus nerve B-and C-fibre potentials were prolonged.
In 4-AP solution (0.1–0.3 mmol/l), GABA (0.1 mmol/l), 3-aminopropanesulphonic acid or muscimol evoked bursts of spikes and EPSPs in addition to a neuronal depolarization. These bursts, which were not elicited by glycine, glutamate, taurine or (±)-baclofen, were completely antagonised by hexamethonium, tetrodotoxin or bicuculline methochloride.
It is concluded that: (a) 4-AP has a potent presynaptic action on sympathetic ganglia; (b) presynaptic actions of GABA can be recorded postsynaptically in the presence of 4-AP; and (c) the presynaptic GABA-receptors revealed in this condition are similar to those on the postsynaptic membrane
Adsorption and dissociation of molecular oxygen on the (0001) surface of double hexagonal close packed americium
In our continuing attempts to understand theoretically various surface
properties such as corrosion and potential catalytic activity of actinide
surfaces in the presence of environmental gases, we report here the first ab
initio study of molecular adsorption on the double hexagonal packed (dhcp)
americium (0001) surface. Dissociative adsorption is found to be energetically
more favorable compared to molecular adsorption. The most stable configuration
corresponds to a horizontal approach molecular dissociation with the oxygen
atoms occupying neighboring h3 sites, with chemisorption energies at the NSOC
and SOC theoretical levels being 9.395 eV and 9.886 eV, respectively. The
corresponding distances of the oxygen molecule from the surface and
oxygen-oxygen distance were found to be 0.953 Ang. and 3.731 Ang.,
respectively. Overall our calculations indicate that chemisorption energies in
cases with SOC are slightly more stable than the cases with NSOC in the
0.089-0.493 eV range. The work functions and net magnetic moments respectively
increased and decreased in all cases compared with the corresponding quantities
of the bare dhcp Am (0001) surface. The adsorbate-substrate interactions have
been analyzed in detail using the partial charges inside the muffin-tin
spheres, difference charge density distributions, and the local density of
states. The effects, if any, of chemisorption on the Am 5f electron
localization-delocalization characteristics in the vicinity of the Fermi level
are also discussed.Comment: 6 tables, 10 figure
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