523 research outputs found
Equation of state for -stable hot nuclear matter
We provide an equation of state for hot nuclear matter in -equilibrium
by applying a momentum-dependent effective interaction. We focus on the study
of the equation of state of high-density and high-temperature nuclear matter,
containing leptons (electrons and muons) under the chemical equilibrium
condition in which neutrinos have left the system. The conditions of charge
neutrality and equilibrium under -decay process lead first to the
evaluation of proton and lepton fractions and afterwards of internal energy,
free energy, pressure and in total to the equation of state of hot nuclear
matter. Thermal effects on the properties and equation of state of nuclear
matter are assesed and analyzed in the framework of the proposed effective
interaction model. Special attention is dedicated to the study of the
contribution of the components of -stable nuclear matter to the entropy
per particle, a quantity of great interest for the study of structure and
collapse of supernova.Comment: 28 pages, 18 figure
Temperature and momentum dependence of single-particle properties in hot asymmetric nuclear matter
We have studied the effects of momentum dependent interactions on the
single-particle properties of hot asymmetric nuclear matter. In particular, the
single-particle potential of protons and neutrons as well as the symmetry
potential have been studied within a self-consistent model using a momentum
dependent effective interaction. In addition, the isospin splitting of the
effective mass has been derived from the above model. In each case temperature
effects have been included and analyzed. The role of the specific
parametrization of the effective interaction used in the present work has been
investigated. It has been concluded that the behavior of the symmetry potential
depends strongly on the parametrization of the interaction part of the energy
density and the momentum dependence of the regulator function. The effects of
the parametrization have been found to be less pronounced on the isospin mass
splitting.Comment: 22 pages, 14 figure
Equation of state for dense supernova matter
We provide an equation of state for high density supernova matter by applying
a momentum-dependent effective interaction. We focus on the study of the
equation of state of high-density and high-temperature nuclear matter
containing leptons (electrons and neutrinos) under the chemical equilibrium
condition. The conditions of charge neutrality and equilibrium under
-decay process lead first to the evaluation of the lepton fractions and
afterwards the evaluation of internal energy, pressure, entropy and in total to
the equation of state of hot nuclear matter for various isothermal cases.
Thermal effects on the properties and equation of state of nuclear matter are
evaluated and analyzed in the framework of the proposed effective interaction
model. Since supernova matter is characterized by a constant entropy we also
present the thermodynamic properties for isentropic case. Special attention is
dedicated to the study of the contribution of the components of -stable
nuclear matter to the entropy per particle, a quantity of great interest for
the study of structure and collapse of supernova.Comment: 23 pages, 15 figure
Lifetime Measurements in 120Xe
Lifetimes for the lowest three transitions in the nucleus Xe have
been measured using the Recoil Distance Technique. Our data indicate that the
lifetime for the transition is more than a factor of
two lower than the previously adopted value and is in keeping with more recent
measurements performed on this nucleus. The theoretical implications of this
discrepancy and the possible reason for the erroneous earlier results are
discussed. All measured lifetimes in Xe, as well as the systematics of
the lifetimes of the 2 states in Xe isotopes, are compared with
predictions of various models. The available data are best described by the
Fermion Dynamic Symmetry Model (FDSM).Comment: 9 pages, RevTeX, 3 figures with Postscript file available on request
at [email protected], [email protected]. Submitted to Phys.
Rev.
Shifting the quantum Hall plateau level in a double layer electron system
We study the plateaux of the integer quantum Hall resistance in a bilayer
electron system in tilted magnetic fields. In a narrow range of tilt angles and
at certain magnetic fields, the plateau level deviates appreciably from the
quantized value with no dissipative transport emerging. A qualitative account
of the effect is given in terms of decoupling of the edge states corresponding
to different electron layers/Landau levels.Comment: 3 pages, 3 figures include
A new window on Strange Quark Matter as the ground state of strongly interacting matter
If strange quark matter is the true ground state of matter, it must have
lower energy than nuclear matter. Simultaneously, two-flavour quark matter must
have higher energy than nuclear matter, for otherwise the latter would convert
to the former. We show, using an effective chiral lagrangian, that the
existence of a new lower energy ground state for two-flavour quark matter, the
pion condensate, shrinks the window for strange quark matter to be the ground
state of matter and sets new limits on the current strange quark mass
A fully relativistic radial fall
Radial fall has historically played a momentous role. It is one of the most
classical problems, the solutions of which represent the level of understanding
of gravitation in a given epoch. A {\it gedankenexperiment} in a modern frame
is given by a small body, like a compact star or a solar mass black hole,
captured by a supermassive black hole. The mass of the small body itself and
the emission of gravitational radiation cause the departure from the geodesic
path due to the back-action, that is the self-force. For radial fall, as any
other non-adiabatic motion, the instantaneous identity of the radiated energy
and the loss of orbital energy cannot be imposed and provide the perturbed
trajectory. In the first part of this letter, we present the effects due to the
self-force computed on the geodesic trajectory in the background field.
Compared to the latter trajectory, in the Regge-Wheeler, harmonic and all
others smoothly related gauges, a far observer concludes that the self-force
pushes inward (not outward) the falling body, with a strength proportional to
the mass of the small body for a given large mass; further, the same observer
notes an higher value of the maximal coordinate velocity, this value being
reached earlier on during infall. In the second part of this letter, we
implement a self-consistent approach for which the trajectory is iteratively
corrected by the self-force, this time computed on osculating geodesics.
Finally, we compare the motion driven by the self-force without and with
self-consistent orbital evolution. Subtle differences are noticeable, even if
self-force effects have hardly the time to accumulate in such a short orbit.Comment: To appear in Int. J. Geom. Meth. Mod. Phy
Stellar and thermal neutron capture cross section of ⁹Be
The neutron capture cross section of ⁹Be for stellar energies was measured via the activation technique using the Karlsruhe Van de Graaff accelerator in combination with accelerator mass spectrometry at the Vienna Environmental Research Accelerator. To characterize the energy region of interest for astrophysical
applications, activations were performed in a quasistellar neutron spectrum of kT = 25 keV and for a spectrum
at En = 473 ± 53 keV. Despite the very small cross section, the method used provided the required sensitivity for
obtaining fairly accurate results of 10.4 ± 0.6 and 8.4 ± 1.0 μb, respectively. With these data it was possible to
constrain the cross section shape up to the first resonances at 622 and 812 keV, thus allowing for the determination
of Maxwellian-averaged cross sections at thermal energies between kT = 5 and 100 keV. In addition, we report
a new experimental cross section value at thermal energy of σth = 8.31 ± 0.52 mb.This work was partly funded by the Austrian Science
Fund (FWF), Projects No. P20434 and No. I428, and by
the Australian Research Council, Projects No. DP140100136
and No. DP180100496
Abundance of live ²⁴⁴Pu in deep-sea reservoirs on earth points to rarity of actinide nucleosynthesis
Quark Hadron Phase Transition and Hybrid Stars
We investigate the properties of hybrid stars consisting of quark matter in
the core and hadron matter in outer region. The hadronic and quark matter
equations of state are calculated by using nonlinear Walecka model and chiral
colour dielectric (CCD) model respectively. We find that the phase transition
from hadron to quark matter is possible in a narrow range of the parameters of
nonlinear Walecka and CCD models. The transition is strong or weak first order
depending on the parameters used. The EOS thus obtained, is used to study the
properties of hybrid stars. We find that the calculated hybrid star properties
are similar to those of pure neutron stars.Comment: 25 pages in LaTex and 9 figures available on request, IP/BBSR/94-3
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