17,131 research outputs found
Connection between slow and fast dynamics of molecular liquids around the glass transition
The mean-square displacement (MSD) was measured by neutron scattering at
various temperatures and pressures for a number of molecular glass-forming
liquids. The MSD is invariant along the glass-transition line at the pressure
studied, thus establishing an ``intrinsic'' Lindemann criterion for any given
liquid. A one-to-one connection between the MSD's temperature dependence and
the liquid's fragility is found when the MSD is evaluated on a time scale of
approximately 4 nanoseconds, but does not hold when the MSD is evaluated at
shorter times. The findings are discussed in terms of the elastic model and the
role of relaxations, and the correlations between slow and fast dynamics are
addressed.Comment: accepted by Phys Rev E (2010
On the normalization of Killing vectors and energy conservation in two-dimensional gravity
We explicitly show that, in the context of a recently proposed 2D dilaton
gravity theory, energy conservation requires the ``natural'' Killing vector to
have, asymptotically, an unusual normalization. The Hawking temperature
is then calculated according to this prescription.Comment: 7 pages, Latex, no figure
Universality and Scaling at the Onset of Quantum Black Hole Formation
In certain two-dimensional models, collapsing matter forms a black hole if
and only if the incoming energy flux exceeds the Hawking radiation rate. Near
the critical threshold, the black hole mass is given by a universal formula in
terms of the distance from criticality, and there exists a scaling solution
describing the formation and evaporation of an arbitrarily small black hole.Comment: 9 pages, 3 figures (uuencoded
Real decoupling ghost quantization of the CGHS model for two dimensional black holes
A complete RST quantization of a CGHS model plus Strominger term is carried
out. In so doing a conformal invariant theory with is
found, that is, without ghosts contribution. The physical consequences of the
model are analysed and positive definite Hawking radiation is found.Comment: 14 pages, latex, no figures, marginal errors correcte
Condensation of Tubular D2-branes in Magnetic Field Background
It is known that in the Minkowski vacuum a bunch of IIA superstrings with
D0-branes can be blown-up to a supersymmetric tubular D2-brane, which is
supported against collapse by the angular momentum generated by crossed
electric and magnetic Born-Infeld (BI) fields. In this paper we show how the
multiple, smaller tubes with relative angular momentum could condense to a
single, larger tube to stabilize the system. Such a phenomena could also be
shown in the systems under the Melvin magnetic tube or uniform magnetic field
background. However, depending on the magnitude of field strength, a tube in
the uniform magnetic field background may split into multiple, smaller tubes
with relative angular momentum to stabilize the system.Comment: Latex 10 pages, mention the dynamical joining of the tubes, modify
figure
Model of black hole evolution
From the postulate that a black hole can be replaced by a boundary on the
apparent horizon with suitable boundary conditions, an unconventional scenario
for the evolution emerges. Only an insignificant fraction of energy of order
is radiated out. The outgoing wave carries a very small part of the
quantum mechanical information of the collapsed body, the bulk of the
information remaining in the final stable black hole geometry.Comment: 9 pages, harvmac, 3 figures, minor addition
Model of black hole evolution
From the postulate that a black hole can be replaced by a boundary on the
apparent horizon with suitable boundary conditions, an unconventional scenario
for the evolution emerges. Only an insignificant fraction of energy of order
is radiated out. The outgoing wave carries a very small part of the
quantum mechanical information of the collapsed body, the bulk of the
information remaining in the final stable black hole geometry.Comment: 9 pages, harvmac, 3 figures, minor addition
Soluble models in 2d dilaton gravity
A one-parameter class of simple models of two-dimensional dilaton gravity,
which can be exactly solved including back-reaction effects, is investigated at
both classical and quantum levels. This family contains the RST model as a
special case, and it continuously interpolates between models having a flat
(Rindler) geometry and a constant curvature metric with a non-trivial dilaton
field. The processes of formation of black hole singularities from collapsing
matter and Hawking evaporation are considered in detail. Various physical
aspects of these geometries are discussed, including the cosmological
interpretation.Comment: 15 pages, harvmac, 3 figure
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