32,588 research outputs found
Consistency between dynamical and thermodynamical stabilities for perfect fluid in theories
We investigate the stability criterions for perfect fluid in theories
which is an important generalization of general relativity. Firstly, using
Wald's general variation principle, we recast Seifert's work and obtain the
dynamical stability criterion. Then using our generalized thermodynamical
criterion, we obtain the concrete expressions of the criterion. We show that
the dynamical stability criterion is exactly the same as the thermodynamical
stability criterion. This result suggests that there is an inherent connection
between the thermodynamics and gravity in theories. It should be pointed
out that using the thermodynamical method to determine the stability for
perfect fluid is simpler and more directly than the dynamical method.Comment: 18page
Thermodynamical stability for perfect fluid
According to maximum entropy principle, it has been proved that the
gravitational field equations could be derived by the extrema of total entropy
for perfect fluid, which implies that thermodynamic relations contain
information of gravity. In this manuscript, we obtain a criterion for
thermodynamical stability of an adiabatic, self-gravitating perfect fluid
system by the second variation of total entropy. We show, for Einstein's
gravity with spherical symmetry spacetime, that the criterion is consistent
with that for dynamical stability derived by Chandrasekhar and Wald. We also
find that the criterion could be applied to cases without spherical symmetry,
or under general perturbations. The result further establishes the connection
between thermodynamics and gravity.Comment: 10 page
Holographic Van der Waals-like phase transition in the Gauss-Bonnet gravity
The Van der Waals-like phase transition is observed in temperature-thermal
entropy plane in spherically symmetric charged Gauss-Bonnet-AdS black hole
background. In terms of AdS/CFT, the non-local observables such as holographic
entanglement entropy, Wilson loop, and two point correlation function of very
heavy operators in the field theory dual to spherically symmetric charged
Gauss-Bonnet-AdS black hole have been investigated. All of them exhibit the Van
der Waals-like phase transition for a fixed charge parameter or Gauss-Bonnet
parameter in such gravity background. Further, with choosing various values of
charge or Gauss-Bonnet parameter, the equal area law and the critical exponent
of the heat capacity are found to be consistent with phase structures in
temperature-thermal entropy plane.Comment: Some statements about the analogy between the black hole phase
transition in plane and Van der Waals-like phase transition in
plane are added. This is the published versio
Stabilized Structure from Motion without Disparity Induces Disparity Adaptation
3D structures can be perceived based on the patterns of 2D motion signals [1, 2]. With orthographic projection of a 3D stimulus onto a 2D plane, the kinetic information can give a vivid impression of depth, but the depth order is intrinsically ambiguous, resulting in bistable or even multistable interpretations [3]. For example, an orthographic projection of dots on the surface of a rotating cylinder is perceived as a rotating cylinder with ambiguous direction of rotation [4]. We show that the bistable rotation can be stabilized by adding information, not to the dots themselves, but to their spatial context. More interestingly, the stabilized bistable motion can generate consistent rotation aftereffects. The rotation aftereffect can only be observed when the adapting and test stimuli are presented at the same stereo depth and the same retinal location, and it is not due to attentional tracking. The observed rotation aftereffect is likely due to direction-contingent disparity adaptation, implying that stimuli with kinetic depth may have activated neurons sensitive to different disparities, even though the stimuli have zero relative disparity. Stereo depth and kinetic depth may be supported by a common neural mechanism at an early stage in the visual system
Constraints on primordial black holes and primeval density perturbations from the epoch of reionization
We investigate the constraint on the abundance of primordial black holes
(PBHs) and the spectral index of primeval density perturbations given by
the ionizing photon background at the epoch of reionization. Within the
standard inflationary cosmogony, we show that the spectral index of the
power-law power spectrum of primeval density perturbations should be 1.27.
Since the universe is still optical thick at the reionization redshift - 8, this constraint is independent of the unknown parameter of reheating
temperature of the inflation. The ionizing photon background from the PBHs can
be well approximated by a power law spectrum , which is
greatly different from those given by models of massive stars and quasars.Comment: 4 pages, 3 eps figues, to be published in ApJ Letter
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