2,581 research outputs found
Gravitational waves and neutrino emission from the merger of binary neutron stars
Numerical simulations for the merger of binary neutron stars are performed in
full general relativity incorporating a finite-temperature (Shen's) equation of
state (EOS) and neutrino cooling for the first time. It is found that for this
stiff EOS, a hypermassive neutron star (HMNS) with a long lifetime (
ms) is the outcome for the total mass \alt 3.0M_{\odot}. It is shown that the
typical total neutrino luminosity of the HMNS is --
ergs/s and the effective amplitude of gravitational waves from the HMNS is
4-- at --2.5 kHz for a source distance of 100 Mpc. We
also present the neutrino luminosity curve when a black hole is formed for the
first time.Comment: 4 pages, 4 figures (Fig.2 is in low resolution), Accepted for
publication in PR
Non-axisymmetric instabilities of neutron star with toroidal magnetic fields
The aim of this paper is to clarify the stabilities of neutron stars with
strong toroidal magnetic fields against non-axisymmetric perturbation. The
motivation comes from the fact that super magnetized neutron stars of G, magnetars, and magnetized proto-neutron stars born after the
magnetically-driven supernovae are likely to have such strong toroidal magnetic
fields. Long-term, three-dimensional general relativistic magneto-hydrodynamic
simulations are performed, preparing isentropic neutron stars with toroidal
magnetic fields in equilibrium as initial conditions. To explore the effects of
rotations on the stability, simulations are done for both non-rotating and
rigidly rotating models. We find the emergence of the Parker and/or Tayler
instabilities in both the non-rotating and rotating models. For both
non-rotating and rotating models, the Parker instability is the primary
instability as predicted by the local linear perturbation analysis. The
interchange instability also appears in the rotating models. It is found that
rapid rotation is not enough to suppress the Parker instability, and this
finding does not agree with the perturbation analysis. The reason for this is
that rigidly and rapidly rotating stars are marginally stable, and hence, in
the presence of stellar pulsations by which the rotational profile is deformed,
unstable regions with negative gradient of angular momentum profile is
developed. After the onset of the instabilities, a turbulence is excited.
Contrary to the axisymmetric case, the magnetic fields never reach an
equilibrium state after the development of the turbulence. This conclusion
suggests that three-dimensional simulation is indispensable for exploring the
formation of magnetars or prominence activities of magnetars such as giant
flares.Comment: 19 pages, 11 figures, to be published in A&
Design of Practical Superconducting DC Power Cable With REBCO Coated Conductors
critical current density of a superconductor in a parallel magnetic field. It was expected that a cable with a high current-carrying capacity could be realized with REBa2Cu3O7-σ (REBCO) coated conductors. However, the critical current density in most commercial coated conductors does not increase but slightly decreases with increasing parallel magnetic field. Nevertheless, the critical current density in the parallel magnetic field is remarkably higher than that in a normal in-plane magnetic field, and it is possible to construct a dc cable with a higher current-carrying capacity using this characteristic in comparison with conventional superconducting cables. In this paper, we propose a new design of dc power cable suitable for present commercial coated conductors. The optimal condition of the cable is discussed
Relativistic stars with purely toroidal magnetic fields
We investigate the effects of the purely toroidal magnetic field on the
equilibrium structures of the relativistic stars. The master equations for
obtaining equilibrium solutions of relativistic rotating stars containing
purely toroidal magnetic fields are derived for the first time. To solve these
master equations numerically, we extend the Cook-Shapiro-Teukolsky scheme for
calculating relativistic rotating stars containing no magnetic field to
incorporate the effects of the purely toroidal magnetic fields. By using the
numerical scheme, we then calculate a large number of the equilibrium
configurations for a particular distribution of the magnetic field in order to
explore the equilibrium properties. We also construct the equilibrium sequences
of the constant baryon mass and/or the constant magnetic flux, which model the
evolution of an isolated neutron star as it loses angular momentum via the
gravitational waves. Important properties of the equilibrium configurations of
the magnetized stars obtained in this study are summarized as follows ; (1) For
the non-rotating stars, the matter distribution of the stars is prolately
distorted due to the toroidal magnetic fields. (2) For the rapidly rotating
stars, the shape of the stellar surface becomes oblate because of the
centrifugal force. But, the matter distribution deep inside the star is
sufficiently prolate for the mean matter distribution of the star to be
prolate. (3) The stronger toroidal magnetic fields lead to the mass-shedding of
the stars at the lower angular velocity. (4) For some equilibrium sequences of
the constant baryon mass and magnetic flux, the stars can spin up as they lose
angular momentum.Comment: 13 figures, 7 tables, submitted to PR
Evaluation of trapped magnetic field properties in superconducting MgB2 bulk magnets by finite element method
The trapped magnetic field properties in superconducting MgB2 bulk magnets with various kinds of shape such as a disk, a ring and a pair of disks were calculated by the finite element method (FEM). For simplicity, field cool magnetization was replaced by a simple magnetization process at constant temperature to obtain equivalent distribution of magnetic field, and the thermal equation in FEM was omitted. It was confirmed that the result of FEM agreed well with the result by analytical method in infinite long cylinder. We compared the trapped magnetic field property between FEM result and experimental result in reference in order to research the simple evaluation method of the trapped magnetic field of MgB2 bulk magnet. It was found that the result of FEM agreed with the experimental result and it can explain the distribution of trapped magnetic field of superconducting MgB2 bulk magnet. From these results, it was found that it was possible to be calculated in various kinds of shape with using simple evaluation by FEM. Therefore, the optimization of the maximum trapped magnetic field in superconducting MgB2 bulk magnet can be discussed.Proceedings of the 27th International Symposium on Superconductivity (ISS 2014) November 25-27, 2014, Tokyo, Japa
Estimation of AC loss in cylindrical superconductor with ripple current
The loss energy density (AC loss) in cylindrical superconductor with ripple current based on Irie-Yamafuji model in which the magnetic fiel dependence of critical current density is taken into account is theoretically calculated for design of DC transmission cable system. It is confirme that the AC loss does not changed for the cases with and without DC current when the critical current does not depend on magnetic fiel which is corresponding to Bean-London model. On the contrary, it is found that there is current region where the AC loss becomes smaller than that for the case without DC current. The AC loss of ripple current is seems to be enough small in layered structure of DC transmission cable made by thin tape superconductor.Proceedings of the 24th International Symposium on Superconductivity (ISS 2011), October 24-26, 2011, Tokyo, Japa
The experimental challenge of detecting solar axion-like particles to test cosmological ALP-photon oscillation hypothesis
We consider possible experimental tests of recent hypotheses suggesting that
TeV photons survive the pair production interaction with extragalactic
background light over cosmological distances by converting to axion-like
particles (ALPs) in galactic magnetic fields. We show that proposed giant
ultra-low background scintillation detectors will even have a difficult time
reaching the present CAST sensitivity, which is one to two orders of magnitude
less sensitive than necessary for a meaningful test of the ALP-photon
oscillation hypothesis. Potential alternative tests are briefly discussed.Comment: 4 pages, no figure
General-relativistic neutrino-radiation magnetohydrodynamics simulation of black hole-neutron star mergers for seconds
Seconds-long numerical-relativity simulations for black hole-neutron star mergers are performed for the first time to obtain a self-consistent picture of the merger and post-merger evolution processes. To investigate the case that tidal disruption takes place, we choose the initial mass of the black hole to be or with the dimensionless spin of 0.75. The neutron-star mass is fixed to be . We find that after the tidal disruption, dynamical mass ejection takes place spending together with the formation of a massive accretion disk. Subsequently, the magnetic field in the disk is amplified by the magnetic winding and magnetorotational instability, establishing a turbulent state and inducing the angular momentum transport. The post-merger mass ejection by the magnetically-induced viscous effect sets in at - after the tidal disruption, at which the neutrino luminosity drops below , and continues for several hundreds ms. A magnetosphere near the rotational axis of the black hole is developed after the matter and magnetic flux fall into the black hole from the accretion disk, and high-intensity Poynting flux generation sets in at a few hundreds ms after the tidal disruption. The intensity of the Poynting flux becomes low after the significant post-merger mass ejection, because the opening angle of the magnetosphere increases. The lifetime for the stage with the strong Poynting flux is -, which agrees with the typical duration of short-hard gamma-ray bursts
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