391 research outputs found
Liquid-gas phase transition and Coulomb instability of asymmetric nuclear systems
We use a chiral SU(3) quark mean field model to study the properties of
nuclear systems at finite temperature. The liquid-gas phase transition of
symmetric and asymmetric nuclear matter is discussed. For two formulations of
the model the critical temperature, , for symmetric nuclear matter is
found to be 15.8 MeV and 17.9 MeV. These values are consistent with those
derived from recent experiments. The limiting temperatures for finite nuclei
are in good agreement with the experimental points.Comment: 14 pages, 6 figure
Liquid-gas phase transition and Coulomb instability of asymmetric nuclear systems
We use a chiral SU(3) quark mean field model to study the properties of
nuclear systems at finite temperature. The liquid-gas phase transition of
symmetric and asymmetric nuclear matter is discussed. For two formulations of
the model the critical temperature, , for symmetric nuclear matter is
found to be 15.8 MeV and 17.9 MeV. These values are consistent with those
derived from recent experiments. The limiting temperatures for finite nuclei
are in good agreement with the experimental points.Comment: 14 pages, 6 figure
New treatment of the chiral SU(3) quark mean field model
We perform a study of infinite hadronic matter, finite nuclei and hypernuclei
with an improved method of calculating the effective baryon mass. A detailed
study of the predictions of the model is made in comparison with the available
data and the level of agreement is generally very good. Comparison with an
earlier treatment shows relatively minor differences at or below normal nuclear
matter density, while at high density the improved calculation is quite
different. In particular, we find no phase transition corresponding to chiral
symmetry restoration in high density nuclear matter.Comment: 19 pages, 11 figure
Color-Neutral Superconducting Quark Matter
We investigate the consequences of enforcing local color neutrality on the
color superconducting phases of quark matter by utilizing the
Nambu-Jona-Lasinio model supplemented by diquark and the t'Hooft six-fermion
interactions. In neutrino free matter at zero temperature, color neutrality
guarantees that the number densities of u, d, and s quarks in the
Color-Flavor-Locked (CFL) phase will be equal even with physical current quark
masses. Electric charge neutrality follows as a consequence and without the
presence of electrons. In contrast, electric charge neutrality in the less
symmetric 2-flavor superconducting (2SC) phase with ud pairing requires more
electrons than the normal quark phase. The free energy density cost of
enforcing color and electric charge neutrality in the CFL phase is lower than
that in the 2SC phase, which favors the formation of the CFL phase. With
increasing temperature and neutrino content, an unlocking transition occurs
from the CFL phase to the 2SC phase with the order of the transition depending
on the temperature, the quark and lepton number chemical potentials. The
astrophysical implications of this rich structure in the phase diagram,
including estimates of the effects from Goldstone bosons in the CFL phase, are
discussed.Comment: 20 pages, 4 figures; version to appear in Phys. Rev.
Drum vortons in high density QCD
Recently it was shown that high density QCD supports of number of topological
defects. In particular, there are U(1)_Y strings that arise due to K^0
condensation that occurs when the strange quark mass is relatively large. The
unique feature of these strings is that they possess a nonzero K^+ condensate
that is trapped on the core. In the following we will show that these strings
(with nontrivial core structure) can form closed loops with conserved charge
and currents trapped on the string worldsheet. The presence of conserved
charges allows these topological defects, called vortons, to carry angular
momentum, which makes them classically stable objects. We also give arguments
demonstrating that vortons carry angular momentum very efficiently (in terms of
energy per unit angular momentum) such that they might be the important degrees
of freedom in the cores of neutron stars.Comment: 11 pages, accepted for publication in Physical Review
Transverse oscillations of coronal loops
On 14 July 1998 TRACE observed transverse oscillations of a coronal loop generated by an external disturbance most probably caused by a solar flare. These oscillations were interpreted as standing fast kink waves in a magnetic flux tube. Firstly, in this review we embark on the discussion of the theory of waves and oscillations in a homogeneous straight magnetic cylinder with the particular emphasis on fast kink waves. Next, we consider the effects of stratification, loop expansion, loop curvature, non-circular cross-section, loop shape and magnetic twist.
An important property of observed transverse coronal loop oscillations is their fast damping. We briefly review the different mechanisms suggested for explaining the rapid damping phenomenon. After that we concentrate on damping due to resonant absorption. We describe the latest analytical results obtained with the use of thin transition layer approximation, and then compare these results with numerical findings obtained for arbitrary density variation inside the flux tube.
Very often collective oscillations of an array of coronal magnetic loops are observed. It is natural to start studying this phenomenon from the system of two coronal loops. We describe very recent analytical and numerical results of studying collective oscillations of two parallel homogeneous coronal loops.
The implication of the theoretical results for coronal seismology is briefly discussed. We describe the estimates of magnetic field magnitude obtained from the observed fundamental frequency of oscillations, and the estimates of the coronal scale height obtained using the simultaneous observations of the fundamental frequency and the frequency of the first overtone of kink oscillations.
In the last part of the review we summarise the most outstanding and acute problems in the theory of the coronal loop transverse oscillations
Instanton Effects in QCD at High Baryon Density
We study instanton effects in QCD at very high baryon density. In this regime
instantons are suppressed by a large power of , where
is the QCD scale parameter and is the baryon chemical
potential. Instantons are nevertheless important because they contribute to
several physical observables that vanish to all orders in perturbative QCD. We
study, in particular, the chiral condensate and its contribution to the masses of Goldstone bosons in the CFL phase of QCD
with flavors. We find that at densities , where
is the density of nuclear matter, the result is dominated by large
instantons and subject to considerable uncertainties. We suggest that these
uncertainties can be addressed using lattice calculations of the instanton
density and the pseudoscalar diquark mass in QCD with two colors. We study the
topological susceptibility and Witten-Veneziano type mass relations in both
and QCD.Comment: 27 pages, 8 figures, minor revision
Neutrino Emission from Goldstone Modes in Dense Quark Matter
We calculate neutrino emissivities from the decay and scattering of Goldstone
bosons in the color-flavor-locked (CFL) phase of quarks at high baryon density.
Interactions in the CFL phase are described by an effective low-energy theory.
For temperatures in the tens of keV range, relevant to the long-term cooling of
neutron stars, the emissivities involving Goldstone bosons dominate over those
involving quarks, because gaps in the CFL phase are MeV while the
masses of Goldstone modes are on the order of 10 MeV. For the same reason, the
specific heat of the CFL phase is also dominated by the Goldstone modes.
Notwithstanding this, both the emissivity and the specific heat from the
massive modes remain rather small, because of their extremely small number
densities. The values of the emissivity and the specific heat imply that the
timescale for the cooling of the CFL core in isolation is y,
which makes the CFL phase invisible as the exterior layers of normal matter
surrounding the core will continue to cool through significantly more rapid
processes. If the CFL phase appears during the evolution of a proto-neutron
star, neutrino interactions with Goldstone bosons are expected to be
significantly more important since temperatures are high enough (
MeV) to admit large number densities of Goldstone modes.Comment: 29 pages, no figures. slightly modified text, one new eqn. and new
refs. adde
Dermatophylosis in Santa InĂȘs sheep from Distrito Federal
Relataram-se quatro casos de dermatofilose em ovinos da raça Santa InĂȘs, no perĂodo de um ano. Microscopicamente observaram-se filamentos na forma de "trilho de bonde" e zoĂłsporos nos quatro casos. A tentativa do isolamento do microrganismo foi realizada por meio do mĂ©todo de Haalstra e em apenas um caso obteve-se sucesso, observando-se colĂŽnias de aparĂȘncia lisa, formato circular, cor amarelada e hemolĂtica em ĂĄgar sangue. O exame direto com coloração de Gram mostrou-se um mĂ©todo bastante eficiente na confirmação da presença do microrganismo afetando a epiderme em razĂŁo da morfologia tĂpica do agente.Four cases of dermatophylosis were reported in Santa InĂȘs sheep in a study period of one year. Microscopically, septate filaments and coccoid forms zoospores were observed. Attempts to isolate the microorganisms were accomplished using Haastra's method and it was successful in only one case. Dermatophilus congolensis samples have grown on blood agar, colonies where hemolytic, small, round and pigmentation vary from yellow to orange. The gram staining method was efficient to confirm the presence of the microorganism affecting the epidermis due to typical morphology of the agent
- âŠ