17,227 research outputs found

### Gravitational waves from axisymmetrically oscillating neutron stars in general relativistic simulations

Gravitational waves from oscillating neutron stars in axial symmetry are
studied performing numerical simulations in full general relativity. Neutron
stars are modeled by a polytropic equation of state for simplicity. A
gauge-invariant wave extraction method as well as a quadrupole formula are
adopted for computation of gravitational waves. It is found that the
gauge-invariant variables systematically contain numerical errors generated
near the outer boundaries in the present axisymmetric computation. We clarify
their origin, and illustrate it possible to eliminate the dominant part of the
systematic errors. The best corrected waveforms for oscillating and rotating
stars currently contain errors of magnitude $\sim 10^{-3}$ in the local wave
zone. Comparing the waveforms obtained by the gauge-invariant technique with
those by the quadrupole formula, it is shown that the quadrupole formula yields
approximate gravitational waveforms besides a systematic underestimation of the
amplitude of $O(M/R)$ where $M$ and $R$ denote the mass and the radius of
neutron stars. However, the wave phase and modulation of the amplitude can be
computed accurately. This indicates that the quadrupole formula is a useful
tool for studying gravitational waves from rotating stellar core collapse to a
neutron star in fully general relativistic simulations. Properties of the
gravitational waveforms from the oscillating and rigidly rotating neutron stars
are also addressed paying attention to the oscillation associated with
fundamental modes

### Emulsion chamber observations and interpretation (HE 3)

Experimental results from Emulsion Chamber (EC) experiments at mountain altitudes or at higher levels using flying carriers are examined. The physical interest in this field is concentrated on the strong interaction at the very high energy region exceeding the accelerator energy, also on the primary cosmic ray intensity and its chemical composition. Those experiments which observed cosmic ray secondaries gave information on high energy interaction characteristics through the analyses of secondary spectra, gamma-hadron families and C-jets (direct observation of the particle production occuring at the carbon target). Problems of scaling violation in fragmentation region, interaction cross section, transverse momentum of produced secondaries, and some peculiar features of exotic events are discussed

### Merger of binary neutron stars of unequal mass in full general relativity

We present results of three dimensional numerical simulations of the merger
of unequal-mass binary neutron stars in full general relativity. A $\Gamma$-law
equation of state $P=(\Gamma-1)\rho\epsilon$ is adopted, where $P$, $\rho$,
\varep, and $\Gamma$ are the pressure, rest mass density, specific internal
energy, and the adiabatic constant, respectively. We take $\Gamma=2$ and the
baryon rest-mass ratio $Q_M$ to be in the range 0.85--1. The typical grid size
is $(633,633,317)$ for $(x,y,z)$ . We improve several implementations since the
latest work. In the present code, the radiation reaction of gravitational waves
is taken into account with a good accuracy. This fact enables us to follow the
coalescence all the way from the late inspiral phase through the merger phase
for which the transition is triggered by the radiation reaction. It is found
that if the total rest-mass of the system is more than $\sim 1.7$ times of the
maximum allowed rest-mass of spherical neutron stars, a black hole is formed
after the merger irrespective of the mass ratios. The gravitational waveforms
and outcomes in the merger of unequal-mass binaries are compared with those in
equal-mass binaries. It is found that the disk mass around the so formed black
holes increases with decreasing rest-mass ratios and decreases with increasing
compactness of neutron stars. The merger process and the gravitational
waveforms also depend strongly on the rest-mass ratios even for the range $Q_M=
0.85$--1.Comment: 32 pages, PRD68 to be publishe

### Thermodynamic properties of the one-dimensional Kondo insulators studied by the density matrix renormalization group method

Thermodynamic properties of the one-dimensional Kondo lattice model at
half-filling are studied by the density matrix renormalization group method
applied to the quantum transfer matrix. Spin susceptibility, charge
susceptibility, and specific heat are calculated down to T=0.1t for various
exchange constants. The obtained results clearly show crossover behavior from
the high temperature regime of nearly independent localized spins and
conduction electrons to the low temperature regime where the two degrees of
freedom couple strongly. The low temperature energy scales of the charge and
spin susceptibilities are determined and shown to be equal to the quasiparticle
gap and the spin gap, respectively, for weak exchange couplings.Comment: 4 pages, 3 Postscript figures, REVTeX, submitted to J. Phys. Soc. Jp

### Gravitational Waves from the Merger of Binary Neutron Stars in a Fully General Relativistic Simulation

We performed 3D numerical simulations of the merger of equal-mass binary
neutron stars in full general relativity using a new large scale supercomputer.
We take the typical grid size as (505,505,253) for (x,y,z) and the maximum grid
size as (633,633,317). These grid numbers enable us to put the outer boundaries
of the computational domain near the local wave zone and hence to calculate
gravitational waveforms of good accuracy (within $\sim 10%$ error) for the
first time. To model neutron stars, we adopt a $\Gamma$-law equation of state
in the form $P=(\Gamma-1)\rho\epsilon$, where P, $\rho$, \varep and $\Gamma$
are the pressure, rest mass density, specific internal energy, and adiabatic
constant. It is found that gravitational waves in the merger stage have
characteristic features that reflect the formed objects. In the case that a
massive, transient neutron star is formed, its quasi-periodic oscillations are
excited for a long duration, and this property is reflected clearly by the
quasi-periodic nature of waveforms and the energy luminosity. In the case of
black hole formation, the waveform and energy luminosity are likely damped
after a short merger stage. However, a quasi-periodic oscillation can still be
seen for a certain duration, because an oscillating transient massive object is
formed during the merger. This duration depends strongly on the initial
compactness of neutron stars and is reflected in the Fourier spectrum of
gravitational waves. To confirm our results and to calibrate the accuracy of
gravitational waveforms, we carried out a wide variety of test simulations,
changing the resolution and size of the computational domain.Comment: 40 pages; pubslihed in Prog. Theor. Phys. 107 (2002), 26

### A relativistic formalism for computation of irrotational binary stars in quasi equilibrium states

We present relativistic hydrostatic equations for obtaining irrotational
binary neutron stars in quasi equilibrium states in 3+1 formalism. Equations
derived here are different from those previously given by Bonazzola,
Gourgoulhon, and Marck, and have a simpler and more tractable form for
computation in numerical relativity. We also present hydrostatic equations for
computation of equilibrium irrotational binary stars in first post-Newtonian
order.Comment: 5 pages, corrected eqs.(2.10), (2.11) and (3.1

### Thermodynamics of doped Kondo insulator in one dimension: Finite Temperature DMRG Study

The finite-temperature density-matrix renormalization-group method is applied
to the one-dimensional Kondo lattice model near half filling to study its
thermodynamics. The spin and charge susceptibilities and entropy are calculated
down to T=0.03t. We find two crossover temperatures near half filling. The
higher crossover temperature continuously connects to the spin gap at half
filling, and the susceptibilities are suppressed around this temperature. At
low temperatures, the susceptibilities increase again with decreasing
temperature when doping is finite. We confirm that they finally approach to the
values obtained in the Tomonaga-Luttinger (TL) liquid ground state for several
parameters. The crossover temperature to the TL liquid is a new energy scale
determined by gapless excitations of the TL liquid. The transition from the
metallic phase to the insulating phase is accompanied by the vanishing of the
lower crossover temperature.Comment: 4 pages, 7 Postscript figures, REVTe

### Axisymmetric general relativistic hydrodynamics: Long-term evolution of neutron stars and stellar collapse to neutron stars and black holes

We report a new implementation for axisymmetric simulation in full general
relativity. In this implementation, the Einstein equations are solved using the
Nakamura-Shibata formulation with the so-called cartoon method to impose an
axisymmetric boundary condition, and the general relativistic hydrodynamic
equations are solved using a high-resolution shock-capturing scheme based on an
approximate Riemann solver. As tests, we performed the following simulations:
(i) long-term evolution of non-rotating and rapidly rotating neutron stars,
(ii) long-term evolution of neutron stars of a high-amplitude damping
oscillation accompanied with shock formation, (iii) collapse of unstable
neutron stars to black holes, and (iv) stellar collapses to neutron stars. The
tests (i)--(iii) were carried out with the $\Gamma$-law equation of state, and
the test (iv) with a more realistic parametric equation of state for
high-density matter. We found that this new implementation works very well: It
is possible to perform the simulations for stable neutron stars for more than
10 dynamical time scales, to capture strong shocks formed at stellar core
collapses, and to accurately compute the mass of black holes formed after the
collapse and subsequent accretion. In conclusion, this implementation is robust
enough to apply to astrophysical problems such as stellar core collapse of
massive stars to a neutron star and black hole, phase transition of a neutron
star to a high-density star, and accretion-induced collapse of a neutron star
to a black hole. The result for the first simulation of stellar core collapse
to a neutron star started from a realistic initial condition is also presented.Comment: 28 pages, to appear in PRD 67, 0440XX (2003

### Solid Chemical Radiation Dosimeter Semiannual Report

Temperature and X-irradiation strength effects on acid production and color changes in solid chemical radiation dosimete

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