3,726 research outputs found
Symmetry relations in chemical kinetics arising from microscopic reversibility
It is shown that the kinetics of time-reversible chemical reactions having
the same equilibrium constant but different initial conditions are closely
related to one another by a directly measurable symmetry relation analogous to
chemical detailed balance. In contrast to detailed balance, however, this
relation does not require knowledge of the elementary steps that underlie the
reaction, and remains valid in regimes where the concept of rate constants is
ill-defined, such as at very short times and in the presence of low activation
barriers. Numerical simulations of a model of isomerization in solution are
provided to illustrate the symmetry under such conditions, and potential
applications in protein folding-unfolding are pointed out.Comment: 4 pages, 1 figure, accepted to Phys Rev Let
T-spheres as a limit of Lemaitre-Tolman-Bondi solutions
In the Tolman model there exist two quite different branches of solutions -
generic Lemaitre-Tolman-Bondi (LTB) ones and T-spheres as a special case. We
show that, nonetheless, T-spheres can be obtained as a limit of the class of
LTB solutions having no origin and extending to infinity with the areal radius
approaching constant. It is shown that all singularities of T-models are
inherited from those of corresponding LBT solutions. In doing so, the disc type
singularity of a T-sphere is the analog of shell-crossing.Comment: 6 pages. 1 Reference added. To appear in Phys. Rev.
Entropic Accelerating Universe
To accommodate the observed accelerated expansion of the universe, one
popular idea is to invoke a driving term in the Friedmann-Lemaitre equation of
dark energy which must then comprise 70% of the present cosmological energy
density. We propose an alternative interpretation which takes into account the
entropy and temperature intrinsic to the horizon of the universe due to the
information holographically stored there. Dark energy is thereby obviated and
the acceleration is due to an entropic force naturally arising from the
information storage on the horizon surface screen. We consider an additional
quantitative approach inspired by surface terms in general relativity and show
that this leads to the entropic accelerating universe.Comment: 14 pages, 1 figure, extended and clarifie
Quintessence and phantom cosmology with non-minimal derivative coupling
We investigate cosmological scenarios with a non-minimal derivative coupling
between the scalar field and the curvature, examining both the quintessence and
the phantom cases in zero and constant potentials. In general, we find that the
universe transits from one de Sitter solution to another, determined by the
coupling parameter. Furthermore, according to the parameter choices and without
the need for matter, we can obtain a Big Bang, an expanding universe with no
beginning, a cosmological turnaround, an eternally contracting universe, a Big
Crunch, a Big Rip avoidance and a cosmological bounce. This variety of
behaviors reveals the capabilities of the present scenario.Comment: 8 pages, 8 figure
Persistence of black holes through a cosmological bounce
We discuss whether black holes could persist in a universe which recollapses
and then bounces into a new expansion phase. Whether the bounce is of classical
or quantum gravitational origin, such cosmological models are of great current
interest. In particular, we investigate the mass range in which black holes
might survive a bounce and ways of differentiating observationally between
black holes formed just after and just before the last bounce. We also discuss
the consequences of the universe going through a sequence of dimensional
changes as it passes through a bounce.Comment: 8 pages, 1 figur
Alternative Methods of Describing Structure Formation in the Lemaitre-Tolman Model
We describe several new ways of specifying the behaviour of Lemaitre-Tolman
(LT) models, in each case presenting the method for obtaining the LT arbitrary
functions from the given data, and the conditions for existence of such
solutions. In addition to our previously considered `boundary conditions', the
new ones include: a simultaneous big bang, a homogeneous density or velocity
distribution in the asymptotic future, a simultaneous big crunch, a
simultaneous time of maximal expansion, a chosen density or velocity
distribution in the asymptotic future, only growing or only decaying
fluctuations. Since these conditions are combined in pairs to specify a
particular model, this considerably increases the possible ways of designing LT
models with desired properties.Comment: Accepted by Phys Rev D. RevTeX 4, 13 pages, no figures. Part of a
series: gr-qc/0106096, gr-qc/0303016, gr-qc/0309119. Replacement contains
very minor correction
Energy dependence on fractional charge for strongly interacting subsystems
The energies of a pair of strongly-interacting subsystems with arbitrary
noninteger charges are examined from closed and open system perspectives. An
ensemble representation of the charge dependence is derived, valid at all
interaction strengths. Transforming from resonance-state ionicity to ensemble
charge dependence imposes physical constraints on the occupation numbers in the
strong-interaction limit. For open systems, the chemical potential is evaluated
using microscopic and thermodynamic models, leading to a novel correlation
between ground-state charge and an electronic temperature.Comment: 4 pages, 3 figs.; as accepted (Phys. Rev. Lett.
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