1,212 research outputs found
Analytical treatment of critical collapse in 2+1 dimensional AdS spacetime: a toy model
We present an exact collapsing solution to 2+1 gravity with a negative
cosmological constant minimally coupled to a massless scalar field, which
exhibits physical properties making it a candidate critical solution. We
discuss its global causal structure and its symmetries in relation with those
of the corresponding continously self-similar solution derived in the
case. Linear perturbations on this background lead to approximate
black hole solutions. The critical exponent is found to be .Comment: 22 pages, 6 figures. Major changes in the discussions of Sects. 2 and
5. The value of the critical exponent has been revised to \gamma = 2/
Spontaneous emission of an atom placed near a nanobelt of elliptical cross-section
Spontaneous emission of an atom (molecule) placed near a nanocylinder of
elliptical cross-section of an arbitrary composition is studied. The analytical
expressions have been obtained for the radiative and nonradiative channels of
spontaneous decay and investigated in details.Comment: 35 pages, 11 figure
TIME-SYMMETRIC INITIAL DATA SETS IN 4--D DILATON GRAVITY
I study the time--symmetric initial--data problem in theories with a massless
scalar field (dilaton), free or coupled to a Maxwell field in the stringy way,
finding different initial--data sets describing an arbitrary number of black
holes with arbitrary masses, charges and asymptotic value of the dilaton. The
presence of the scalar field gives rise to a number of interesting effects. The
mass and charges of a single black hole are different in its two asymptotically
flat regions across the Einstein--Rosen bridge. The same happens to the value
of the dilaton at infinity. This forbids the identification of these asymptotic
regions in order to build (Misner) wormholes in the most naive way. Using
different techniques, I find regular initial data for stringy wormholes. The
price payed is the existence singularities in the dilaton field. The presence
of a single--valued scalar seems to constrain strongly the allowed topologies
of the initial space--like surface. Other kinds of scalar fields (taking values
on a circle or being defined up to an additive constant) are also briefly
considered.Comment: latex file, 38 pages
Predictability and Semiclassical Approximation at the onset of Black Hole formation
We combine analytical and numerical techniques to study the collapse of
conformally coupled massless scalar fields in semiclassical 2D dilaton gravity,
with emphasis on solutions just below criticality when a black hole almost
forms. We study classical information and quantum correlations. We show
explicitly how recovery of information encoded in the classical initial data
from the outgoing classical radiation becomes more difficult as criticality is
approached. The outgoing quantum radiation consists of a positive-energy flux,
which is essentially the standard Hawking radiation, followed by a
negative-energy flux which ensures energy conservation and guarantees unitary
evolution through strong correlations with the positive-energy Hawking
radiation. As one reaches the critical solution there is a breakdown of
unitarity. We show that this breakdown of predictability is intimately related
to a breakdown of the semiclassical approximation.Comment: 26 pages RevTex + 8 figures in a separate postscript fil
Gravitational collapse of massless scalar field and radiation fluid
Several classes of conformally-flat and spherically symmetric exact solutions
to the Einstein field equations coupled with either a massless scalar field or
a radiation fluid are given, and their main properties are studied. It is found
that some represent the formation of black holes due to the gravitational
collapse of the matter fields. When the spacetimes have continuous
self-similarity (CSS), the masses of black holes take a scaling form , where for massless scalar field
and for radiation fluid. The reasons for the difference between
the values of obtained here and those obtained previously are
discussed. When the spacetimes have neither CSS nor DSS (Discrete
self-similarity), the masses of black holes always turn on with finite non-zero
values.Comment: Two figures have been removed, and the text has been re-written. To
appear in Phys. Rev.
Gravitational Collapse of a Radiating Shell
We study the collapse of a self-gravitating and radiating shell. Matter
constituting the shell is quantized and the construction is viewed as a
semiclassical model of possible black hole formation. It is shown that the
shell internal degrees of freedom are excited by the quantum non-adiabaticity
of the collapse and, consequently, on coupling them to a massless scalar field,
the collapsing matter emits a burst of coherent (thermal) radiation.Comment: LaTeX, 34 pages, 21 EPS figures include
The expression of hyperpolarization activated cyclic nucleotide gated (HCN) channels in the rat ovary are dependent on the type of cell and the reproductive age of the animal: a laboratory investigation
<p>Abstract</p> <p>Background</p> <p>Aim of this study was to test the hypothesis that levels of hyperpolarization activated cyclic nucleotide gated channels 1 to 4 (HCN1-4) are linked to the reproductive age of the ovary.</p> <p>Methods</p> <p>Young, adult, and reproductively aged ovaries were collected from Sprague-Dawley rats. RT-PCR and western blot analysis of ovaries was performed to investigate the presence of mRNA and total protein for HCN1-4. Immunohistochemistry with semiquantitative H score analysis was performed using whole ovarian histologic sections.</p> <p>Results</p> <p>RT-PCR analysis showed the presence of mRNA for HCN1-4. Western blot analysis revealed HCN1-3 proteins in all ages of ovarian tissues. Immunohistochemistry with H score analysis demonstrated distinct age-related changes in patterns of HCN1-3 in the oocytes, granulosa cells, theca cells, and corpora lutea. HCN4 was present only in the oocytes, with declining levels during the reproduction lifespan.</p> <p>Conclusion</p> <p>The evidence presented here demonstrates cell-type and developmental age patterns of HCN1-4 channel expression in rat ovaries. Based on this, we hypothesize that HCN channels have functional significance in rat ovaries and may have changing roles in reproductive aging.</p
A Systematic Review of Three-Dimensional Printing in Liver Disease
The purpose of this review is to analyse current literature related to the clinical applications of 3D printed models in liver disease. A search of the literature was conducted to source studies from databases with the aim of determining the applications and feasibility of 3D printed models in liver disease. 3D printed model accuracy and costs associated with 3D printing, the ability to replicate anatomical structures and delineate important characteristics of hepatic tumours, and the potential for 3D printed liver models to guide surgical planning are analysed. Nineteen studies met the selection criteria for inclusion in the analysis. Seventeen of them were case reports and two were original studies. Quantitative assessment measuring the accuracy of 3D printed liver models was analysed in five studies with mean difference between 3D printed models and original source images ranging from 0.2 to 20%. Fifteen studies provided qualitative assessment with results showing the usefulness of 3D printed models when used as clinical tools in preoperative planning, simulation of surgical or interventional procedures, medical education, and training. The cost and time associated with 3D printed liver model production was reported in 11 studies, with costs ranging from US2000, duration of production up to 100 h. This systematic review shows that 3D printed liver models demonstrate hepatic anatomy and tumours with high accuracy. The models can assist with preoperative planning and may be used in the simulation of surgical procedures for the treatment of malignant hepatic tumours
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