104 research outputs found
Naked singularities and quantum gravity
There are known models of spherical gravitational collapse in which the
collapse ends in a naked shell-focusing singularity for some initial data. If a
massless scalar field is quantized on the classical background provided by such
a star, it is found that the outgoing quantum flux of the scalar field diverges
in the approach to the Cauchy horizon. We argue that the semiclassical
approximation (i.e. quantum field theory on a classical curved background) used
in these analyses ceases to be valid about one Planck time before the epoch of
naked singularity formation, because by then the curvature in the central
region of the star reaches Planck scale. It is shown that during the epoch in
which the semiclassical approximation is valid, the total emitted energy is
about one Planck unit, and is not divergent. We also argue that back reaction
in this model does not become important so long as gravity can be treated
classically. It follows that the further evolution of the star will be
determined by quantum gravitational effects, and without invoking quantum
gravity it is not possible to say whether the star radiates away on a short
time scale or settles down into a black hole state.Comment: 16 pages, paper rewritten into sections, conclusions unchanged, 4
references added, to appear in Phys. Rev. D (Rapid Communication
Naked Singularity Explosion
It is known that the gravitational collapse of a dust ball results in naked
singularity formation from an initial density profile which is physically
reasonable. In this paper, we show that explosive radiation is emitted during
the formation process of the naked singularity.Comment: 6 pages, 3 figures, Accepted for Publication in Phys. Rev. D as a
Rapid Communicatio
Physical aspects of naked singularity explosion - How does a naked singularity explode? --
The behaviors of quantum stress tensor for the scalar field on the classical
background of spherical dust collapse is studied. In the previous works
diverging flux of quantum radiation was predicted. We use the exact expressions
in a 2D model formulated by Barve et al. Our present results show that the back
reaction does not become important during the semiclassical phase. The
appearance of the naked singularity would not be affected by this quantum field
radiation. To predict whether the naked singularity explosion occurs or not we
need the theory of quantum gravity. We depict the generation of the diverging
flux inside the collapsing star. The quantum energy is gathered around the
center positively. This would be converted to the diverging flux along the
Cauchy horizon. The ingoing negative flux crosses the Cauchy horizon. The
intensity of it is divergent only at the central naked singularity. This
diverging negative ingoing flux is balanced with the outgoing positive
diverging flux which propagates along the Cauchy horizon. After the replacement
of the naked singularity to the practical high density region the instantaneous
diverging radiation would change to more milder one with finite duration.Comment: 18 pages, 16 figure
Immunohistochemical Examination of a Resected Advanced Hilar Cholangiocarcinoma Arising in a 29-Year-Old Male without Primary Sclerosing Cholangitis
A 29-year-old man with advanced hilar cholangiocarcinoma was successfully treated with an extended right lobectomy. The carbohydrate antigen 19-9 (CA19-9) level was elevated to 939 IU/l, and the pathological findings revealed moderately differentiated tubular adenocarcinoma which involved almost the entire thickness of the hepatic duct and the adjacent liver tissue (T3) and which was associated with lymph node metastasis (N1). It was a stage IIB (T3N1M0) tubular adenocarcinoma according to UICC pathological staging. Immunohistochemical examination revealed that Ki-67, cyclin D1, and MMP-7 were positive, and 14-3-3σ and p27 were negative. The pathological and immunohistochemical findings indicated high malignant potential indicating poor prognosis. We administrated the postoperative adjunct gemcitabine combined with S-1 chemotherapy. The patient is alive without recurrence and doing well two years after surgery. We also review other reports of cholangiocarcinoma patients aged less than 30 years
Topology optimization of nonlinear optical waveguide devices considering output signal phase
A signal output of optical devices with multi-input ports, such as a logic gate, depends on the phase difference between input ports. In order to cascade optical devices, it is essential to design such devices considering not only desired output power but also desired output signal phase. We propose a topology optimization method for optical devices considering the output signal phase. In our approach, the beam propagation method (BPM) is employed as a numerical simulation method and the adjoint variable method (AVM) is used to calculate the sensitivity of output power and signal phase to design parameters. The validity and the effectiveness of our approach are verified through design examples of a three-branching waveguide with linear media and an all-optical logic gate utilizing nonlinear media
Nakedness and curvature strength of shell-focusing singularity in the spherically symmetric space-time with vanishing radial pressure
It was recently shown that the metric functions which describe a spherically
symmetric space-time with vanishing radial pressure can be explicitly
integrated. We investigate the nakedness and curvature strength of the
shell-focusing singularity in that space-time. If the singularity is naked, the
relation between the circumferential radius and the Misner-Sharp mass is given
by with along the first radial
null geodesic from the singularity. The is closely related to the
curvature strength of the naked singularity. For example, for the outgoing or
ingoing null geodesic, if the strong curvature condition (SCC) by Tipler holds,
then must be equal to 1. We define the ``gravity dominance condition''
(GDC) for a geodesic. If GDC is satisfied for the null geodesic, both SCC and
the limiting focusing condition (LFC) by Kr\'olak hold for and
, not SCC but only LFC holds for , and neither
holds for , for the null geodesic. On the other hand, if GDC is
satisfied for the timelike geodesic , both SCC and LFC are satisfied for
the timelike geodesic, irrespective of the value of . Several examples
are also discussed.Comment: 11 pages, Accepted for Publication in Classical and Quantum Gravity,
References Updated, Grammatical Errors Correcte
In Vivo Microwave Ablation of Normal Swine Lung at High-power, Short-duration Settings
To evaluate the volume and heat-sink effects of microwave ablation (MWA) in the ablation zone of the normal swine lung. MWA at 100 W was performed for 1, 2, and 3 min in 7, 5, and 5 lung zones, respectively. We assessed the histopathology in the ablation zones and other outcome measures: namely, length of the longest long and short axes, sphericity, ellipsoid area, and ellipsoid volume. The mean long- and short-axis diameters were 22.0 and 14.1 mm in the 1-min ablation zone, 27.6 and 20.2 mm in the 2-min ablation zone; and 29.2 and 21.2 mm in the 3-min ablation zone, respectively. All measures, except sphericity, were significantly less with 1-min ablation than with either 2- or 3-min ablation. There were no significant differences between the 2- and 3-min ablation zones, but all measures except sphericity were larger with 3-min ablation. Although there were no blood vessels that resulted in a heat-sink effect within the ablation zones, the presence of bronchi nearby in 5 lung ablation zones resulted in reduced ablation size. In high-power, short-duration MWA, the lung ablation volume was affected by ablation time. Some ablations showed that a heat-sink effect by a neighboring bronchus might occur
Naked singularity formation in the collapse of a spherical cloud of counterrotating particles
We investigate collapse of a spherical cloud of counter-rotating particles.
An explicit solution is given using an elliptic integral. If the specific
angular momentum at , no central singularity occurs. With
like that, there is a finite region around the center that bounces. On
the other hand, if the order of is higher than that, a central
singularity occurs. In marginally bound collapse with , a naked
singularity occurs, where is the Misner-Sharp mass. The solution for
this case is expressed by elementary functions. For at
, there is a finite region around the center that bounces and a naked
singularity occurs. For at , there is no such region.
The results suggests that rotation may play a crucial role on the final fate of
collapse.Comment: 6 pages, Accepted for Publication as a Rapid Communication in
Physical Review D, Some Minor Correction
Power, energy, and spectrum of a naked singularity explosion
Naked singularity occurs in the gravitational collapse of an inhomogeneous
dust ball from an initial density profile which is physically reasonable. We
show that explosive radiation is emitted during the formation process of the
naked singularity. The energy flux is proportional to
for a minimally coupled massless scalar field, while is proportional to
for a conformally coupled massless scalar field, where
is the `remained time' until the distant observer could observe
the singularity if the naked singularity was formed. As a consequence, the
radiated energy grows unboundedly for both scalar fields. The amount of the
power and the energy depends on parameters which characterize the initial
density profile but do not depend on the gravitational mass of the cloud. In
particular, there is characteristic frequency of singularity above
which the divergent energy is radiated. The energy flux is dominated by
particles of which the wave length is about at each moment. The
observed total spectrum is nonthermal, i.e., for . If the naked singularity formation could
continue until a considerable fraction of the total energy of the dust cloud is
radiated, the radiated energy would reach about erg. The
calculations are based on the geometrical optics approximation which turns out
to be consistent as a rough order estimate. The analysis does not depend on
whether or not the naked singularity occurs in its exact meaning. This
phenomenon may provide a new candidate for a source of ultra high energy cosmic
rays or a central engine of gamma ray bursts.Comment: 34 pages, 13 postscript figures included, to appear in Phys. Rev. D,
grammatical errors correcte
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