2,074,477 research outputs found
Frustrated Spin System in theta-(BEDT-TTF)_2RbZn(SCN)_4
The origin of the spin gap behavior in the low-temperature dimerized phase of
theta-(BEDT-TTF)_2RbZn(SCN)_4 has been theoretically studied based on the
Hartree-Fock approximation for the on-site Coulomb interaction at absolute
zero. Calculations show that, in the parameter region considered to be relevant
to this compound, antiferromagnetic ordering is stabilized between dimers
consisting of pairs of molecules coupled with the largest transfer integral.
Based on this result an effective localized spin 1/2 model is constructed which
indicates the existence of the frustration among spins. This frustration may
result in the formation of spin gap.Comment: 4 pages, 5 figures, to be published in J. Phys. Soc. Jpn. 67 (1998)
no.
Relativistic Equation of State for Core-Collapse Supernova Simulations
We construct the equation of state (EOS) of dense matter covering a wide
range of temperature, proton fraction, and density for the use of core-collapse
supernova simulations. The study is based on the relativistic mean-field (RMF)
theory, which can provide an excellent description of nuclear matter and finite
nuclei. The Thomas--Fermi approximation in combination with assumed nucleon
distribution functions and a free energy minimization is adopted to describe
the non-uniform matter, which is composed of a lattice of heavy nuclei. We
treat the uniform matter and non-uniform matter consistently using the same RMF
theory. We present two sets of EOS tables, namely EOS2 and EOS3. EOS2 is an
update of our earlier work published in 1998 (EOS1), where only the nucleon
degree of freedom is taken into account. EOS3 includes additional contributions
from hyperons. The effect of hyperons on the EOS is
negligible in the low-temperature and low-density region, whereas it tends to
soften the EOS at high density. In comparison with EOS1, EOS2 and EOS3 have an
improved design of ranges and grids, which covers the temperature range
-- MeV with the logarithmic grid spacing (92 points including T=0), the proton fraction
range --0.65 with the linear grid spacing (66
points), and the density range --
with the logarithmic grid spacing (110 points).Comment: 43 pages, 10 figure
Relativistic Equation of State of Nuclear Matter for Supernova Explosion
We construct the equation of state (EOS) of nuclear matter at finite
temperature and density with various proton fractions within the relativistic
mean field (RMF) theory for the use in the supernova simulations. The
Thomas-Fermi approximation is adopted to describe the non-uniform matter where
we consider nucleus, alpha-particle, proton and neutron in equilibrium. We
treat the uniform matter and non-uniform matter consistently using the RMF
theory. We tabulate the outcome as the pressure, free energy, entropy etc, with
enough mesh points in wide ranges of the temperature, proton fraction, and
baryon mass density.Comment: 22 pages, LaTeX, 9 ps-figures, Submitted to Prog.Theor.Phy
Discovery of {\gamma}-ray pulsation and X-ray emission from the black widow pulsar PSR J2051-0827
We report the discovery of pulsed {\gamma}-ray emission and X-ray emission
from the black widow millisecond pulsar PSR J2051-0827 by using the data from
the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope and
the Advanced CCD Imaging Spectrometer array (ACIS-S) on the Chandra X-ray
Observatory. Using 3 years of LAT data, PSR J2051-0827 is clearly detected in
{\gamma}-ray with a signicance of \sim 8{\sigma} in the 0.2 - 20 GeV band. The
200 MeV - 20 GeV {\gamma}-ray spectrum of PSR J2051-0827 can be modeled by a
simple power- law with a photon index of 2.46 \pm 0.15. Significant (\sim
5{\sigma}) {\gamma}-ray pulsations at the radio period were detected. PSR
J2051-0827 was also detected in soft (0.3-7 keV) X-ray with Chandra. By
comparing the observed {\gamma}-rays and X-rays with theoretical models, we
suggest that the {\gamma}-ray emission is from the outer gap while the X-rays
can be from intra-binary shock and pulsar magnetospheric synchrotron emissions.Comment: 10 pages, 4 figures, accepted by ApJ on Jan 28, 201
Analysis and control of bifurcation and chaos in averaged queue length in TCP/RED model
This paper studies the bifurcation and chaos phenomena in averaged queue length in a
developed Transmission Control Protocol (TCP) model with Random Early Detection
(RED) mechanism. Bifurcation and chaos phenomena are nonlinear behaviour in network
systems that lead to degradation of the network performance. The TCP/RED model used
is a model validated previously. In our study, only the average queue size k q
−
is
considered, and the results are based on analytical model rather than actual measurements.
The instabilities in the model are studied numerically using the conventional nonlinear
bifurcation analysis. Extending from this bifurcation analysis, a modified RED algorithm
is derived to prevent the observed bifurcation and chaos regardless of the selected
parameters. Our modification is for the simple scenario of a single RED router carrying
only TCP traffic. The algorithm neither compromises the throughput nor the average
queuing delay of the system
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