8,388 research outputs found
Thermal effects on nuclear symmetry energy with a momentum-dependent effective interaction
The knowledge of the nuclear symmetry energy of hot neutron-rich matter is
important for understanding the dynamical evolution of massive stars and the
supernova explosion mechanisms. In particular, the electron capture rate on
nuclei and/or free protons in presupernova explosions is especially sensitive
to the symmetry energy at finite temperature. In view of the above, in the
present work we calculate the symmetry energy as a function of the temperature
for various values of the baryon density, by applying a momentum-dependent
effective interaction. In addition to a previous work, the thermal effects are
studied separately both in the kinetic part and the interaction part of the
symmetry energy. We focus also on the calculations of the mean field potential,
employed extensively in heavy ion reaction research, both for nuclear and pure
neutron matter. The proton fraction and the electron chemical potential, which
are crucial quantities for representing the thermal evolution of supernova and
neutron stars, are calculated for various values of the temperature. Finally,
we construct a temperature dependent equation of state of -stable
nuclear matter, the basic ingredient for the evaluation of the neutron star
properties.Comment: 18 pages, 10 figures, 1 table, accepted for publication in Physical
Review
Two-Hop Routing with Traffic-Differentiation for QoS Guarantee in Wireless Sensor Networks
This paper proposes a Traffic-Differentiated Two-Hop Routing protocol for
Quality of Service (QoS) in Wireless Sensor Networks (WSNs). It targets WSN
applications having different types of data traffic with several priorities.
The protocol achieves to increase Packet Reception Ratio (PRR) and reduce
end-to-end delay while considering multi-queue priority policy, two-hop
neighborhood information, link reliability and power efficiency. The protocol
is modular and utilizes effective methods for estimating the link metrics.
Numerical results show that the proposed protocol is a feasible solution to
addresses QoS service differenti- ation for traffic with different priorities.Comment: 13 page
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
Preservation of Woollens Against Clothes Moths & Carpet Beetles
Physico-chemical protective measures employed in various countries all over the World for the preservation of woolens clothes moths & carpet beetles are reviewed
Dynamic crossover scaling in polymer solutions
The crossover region in the phase diagram of polymer solutions, in the regime
above the overlap concentration, is explored by Brownian Dynamics simulations,
to map out the universal crossover scaling functions for the gyration radius
and the single-chain diffusion constant. Scaling considerations, our simulation
results, and recently reported data on the polymer contribution to the
viscosity obtained from rheological measurements on DNA systems, support the
assumption that there are simple relations between these functions, such that
they can be inferred from one another.Comment: 4 pages, 6 figures, 1 Table. Revised version to appear in Physical
Review Letters. Includes supplemental material
Rouse Chains with Excluded Volume Interactions: Linear Viscoelasticity
Linear viscoelastic properties for a dilute polymer solution are predicted by
modeling the solution as a suspension of non-interacting bead-spring chains.
The present model, unlike the Rouse model, can describe the solution's
rheological behavior even when the solvent quality is good, since excluded
volume effects are explicitly taken into account through a narrow Gaussian
repulsive potential between pairs of beads in a bead-spring chain. The use of
the narrow Gaussian potential, which tends to the more commonly used
delta-function repulsive potential in the limit of a width parameter "d" going
to zero, enables the performance of Brownian dynamics simulations. The
simulations results, which describe the exact behavior of the model, indicate
that for chains of arbitrary but finite length, a delta-function potential
leads to equilibrium and zero shear rate properties which are identical to the
predictions of the Rouse model. On the other hand, a non-zero value of "d"
gives rise to a prediction of swelling at equilibrium, and an increase in zero
shear rate properties relative to their Rouse model values. The use of a
delta-function potential appears to be justified in the limit of infinite chain
length. The exact simulation results are compared with those obtained with an
approximate solution which is based on the assumption that the non-equilibrium
configurational distribution function is Gaussian. The Gaussian approximation
is shown to be exact to first order in the strength of excluded volume
interaction, and is found to be accurate above a threshold value of "d", for
given values of chain length and strength of excluded volume interaction.Comment: Revised version. Long chain limit analysis has been deleted. An
improved and corrected examination of the long chain limit will appear as a
separate posting. 32 pages, 9 postscript figures, LaTe
Isospin Fluctuations in QCD and Relativistic Heavy-Ion Collisions
We address the role of fluctuations in strongly interacting matter during the
dense stages of a heavy-ion collision through its electromagnetic emission.
Fluctuations of isospin charge are considered in a thermal system at rest as
well as in a moving hadronic fluid at fixed proper time within a finite bin of
pseudo-rapidity. In the former case, we use general thermodynamic relations to
establish a connection between fluctuations and the space-like screening limit
of the retarded photon self-energy, which directly relates to the emissivities
of dileptons and photons. Effects of hadronic interactions are highlighted
through two illustrative calculations. In the latter case, we show that a
finite time scale inherent in the evolution of a heavy-ion collision
implies that equilibrium fluctuations involve both space-like and time-like
components of the photon self-energy in the system. Our study of non-thermal
effects, explored here through a stochastic treatment, shows that an early and
large fluctuation in isospin survives only if it is accompanied by a large
temperature fluctuation at freeze-out, an unlikely scenario in hadronic phases
with large heat capacity. We point out prospects for the future which include:
(1) A determination of the Debye mass of the system at the dilute freeze-out
stage of a heavy-ion collision, and (2) A delineation of the role of charge
fluctuations during the dense stages of the collision through a study of
electromagnetic emissivities.Comment: 12 pages ReVTeX incl. 4 ps-fig
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