678 research outputs found
Merger of black hole-neutron star binaries: nonspinning black hole case
We perform a simulation for merger of a black hole (BH)-neutron star (NS)
binary in full general relativity preparing a quasicircular state as initial
condition. The BH is modeled by a moving puncture with no spin and the NS by
the -law equation of state with . Corotating velocity field
is assumed for the NS. The mass of the BH and the rest-mass of the NS are
chosen to be and with
relatively large radius of the NS km. The NS is tidally disrupted
near the innermost stable orbit but of the material is swallowed
into the BH with small disk mass even for such small BH
mass . The result indicates that the system of a BH and a
massive disk of is not formed from nonspinning BH-NS binaries,
although a disk of mass is a possible outcome.Comment: 5 pages. Phys. Rev. D 74, 121503 (R) (2006
On the X-ray Image of The Crab Nebula: Comparison with Chandra Observations
An axisymmetric model for the Crab Nebula is constructed to examine the flow
dynamics in the nebula. The model is based on that of Kennel and Coroniti
(1984), although we assume that the kinetic-energy-dominant wind is confined in
an equatorial region. The evolution of the distribution function of the
electron-positron plasma flowing out in the nebula is calculated. Given viewing
angles, we reproduce an image of the nebula and compare it with Chandra
observation.
The reproduced image is not a ring-like but rather 'lip-shaped'. It is found
that the assumption of toroidal field does not reproduce the Chandra image. We
must assume that there is disordered magnetic field with an amplitude as large
as the mean toroidal field. In addition, the brightness contrast between the
front and back sides of the ring cannot be reproduced if we assume that the
magnetization parameter is as small as . The brightness
profile along the semi-major axis of the torus is also examined. The
non-dissipative, ideal-MHD approximation in the nebula appears to break down.
We speculate that if the magnetic energy is released by some process that
produce turbulent field in the nebula flow and causes heating and acceleration,
e.g. by magnetic reconnection, then the present difficulties may be resolved
(i.e. we can reproduce a ring image, and a higher brightness contrast). Thus,
the magnetization parameter can be larger than previously expected.Comment: 8 pages, 4 figures. accepted for publication in MNRA
Inferring the neutron star equation of state from binary inspiral waveforms
The properties of neutron star matter above nuclear density are not precisely
known. Gravitational waves emitted from binary neutron stars during their late
stages of inspiral and merger contain imprints of the neutron-star equation of
state. Measuring departures from the point-particle limit of the late inspiral
waveform allows one to measure properties of the equation of state via
gravitational wave observations. This and a companion talk by J. S. Read
reports a comparison of numerical waveforms from simulations of inspiraling
neutron-star binaries, computed for equations of state with varying stiffness.
We calculate the signal strength of the difference between waveforms for
various commissioned and proposed interferometric gravitational wave detectors
and show that observations at frequencies around 1 kHz will be able to measure
a compactness parameter and constrain the possible neutron-star equations of
state.Comment: Talk given at the 12th Marcel Grossman Meeting, Paris, France, 12-18
Jul 200
Merger of black hole-neutron star binaries in full general relativity
We present our latest results for simulation for merger of black hole
(BH)-neutron star (NS) binaries in full general relativity which is performed
preparing a quasicircular state as initial condition. The BH is modeled by a
moving puncture with no spin and the NS by the -law equation of state
with and corotating velocity field as a first step. The mass of the
BH is chosen to be or , and the rest-mass
of the NS with relatively large radius of the NS
--14 km. The NS is tidally disrupted near the innermost stable
orbit but --90% of the material is swallowed into the BH and resulting
disk mass is not very large as even for small BH mass . The result indicates that the system of a BH and a massive disk
of is not formed from nonspinning BH-NS binaries irrespective
of BH mass, although a disk of mass is a possible outcome
for this relatively small BH mass range as --4. Our results
indicate that the merger of low-mass BH and NS may form a central engine of
short-gamma-ray bursts.Comment: 14 pages. To appear in a special issue of Classical and Quantum
Gravity: New Frontiers in Numerical Relativit
Differentially rotating strange star in general relativity
Rapidly and differentially rotating compact stars are believed to be formed
in binary neutron star merger events, according to both numerical simulations
and the multi-messenger observation of GW170817. The lifetime and evolution of
such a differentially rotating star, is tightly related to the observations in
the post-merger phase. Various studies on the maximum mass of differentially
rotating neutron stars have been done in the past, most of which assume the
so-called -const law as the rotation profile inside the star and consider
only neutron star equations of state. In this paper, we extend the studies to
strange star models, as well as to a new rotation profile model. Significant
differences are found between differentially rotating strange stars and neutron
stars, with both differential rotation laws. A moderate differential rotation
rate for neutron stars is found to be too large for strange stars, resulting in
a rapid drop in the maximum mass as the differential rotation degree is
increased further from , where is a parameter
characterizing the differential rotation rate for -const law. As a result
the maximum mass of a differentially rotating self-bound star drops below the
uniformly rotating mass shedding limit for a reasonable degree of differential
rotation. The continuous transition to the toroidal sequence is also found to
happen at a much smaller differential rotation rate and angular momentum than
for neutron stars. In spite of those differences, -insensitive
relation between the maximum mass for a given angular momentum is still found
to hold, even for the new differential rotation law. Astrophysical consequences
of these differences and how to distinguish between strange star and neutron
star models with future observations are also discussed.Comment: 10 pages, 6 figures
Two cases of bronchiolitis obliterans organizing pneumonia syndrome after postoperative irradiation for breast cancer
We report two cases of bronchiolitis obliterans organizing pneumonia (BOOP) syndrome that developed after postoperative radiation therapy for breast cancer. In both patients, chest radiographs and computed tomography (CT) showed multiple consolidations outside the irradiation
fields after several months of tangential radiation therapy. These patients were diagnosed as having radiation-associated BOOP syndrome, based on their clinical course and the findings on examination. After treatment with a systemic corticosteroid, radiographic consolidations
and symptoms improved rapidly. In cases where consolidations appear outside the irradiated field, it is important to consider BOOP syndrome as a pulmonary complication of radiation therapy for breast cancer
Identification of lactate dehydrogenase as a mammalian pyrroloquinoline quinone (PQQ)-binding protein
Pyrroloquinoline quinone (PQQ), a redox-active o-quinone, is an important nutrient involved in numerous physiological and biochemical processes in mammals. Despite such beneficial functions, the underlying molecular mechanisms remain to be established. In the present study, using PQQ-immobilized Sepharose beads as a probe, we examined the presence of protein(s) that are capable of binding PQQ in mouse NIH/3T3 fibroblasts and identified five cellular proteins, including l-lactate dehydrogenase (LDH) A chain, as potential mammalian PQQ-binding proteins. In vitro studies using a purified rabbit muscle LDH show that PQQ inhibits the formation of lactate from pyruvate in the presence of NADH (forward reaction), whereas it enhances the conversion of lactate to pyruvate in the presence of NAD+ (reverse reaction). The molecular mechanism underlying PQQ-mediated regulation of LDH activity is attributed to the oxidation of NADH to NAD+ by PQQ. Indeed, the PQQ-bound LDH oxidizes NADH, generating NAD+, and significantly catalyzes the conversion of lactate to pyruvate. Furthermore, PQQ attenuates cellular lactate release and increases intracellular ATP levels in the NIH/3T3 fibroblasts. Our results suggest that PQQ, modulating LDH activity to facilitate pyruvate formation through its redox-cycling activity, may be involved in the enhanced energy production via mitochondrial TCA cycle and oxidative phosphorylation
- …