5,884 research outputs found
A Nonsingular Brans Wormhole: An Analogue to Naked Black Holes
In a recent paper, we showed the Jordan frame vacuum Brans Class I solution
provided a wormhole analogue to Horowitz-Ross naked black hole in the wormhole
range -3/2<{\omega}<-4/3. Thereafter, the solution has been criticized by some
authors that, because of the presence of singularity in that solution within
this range, a wormhole interpretation of it is untenable. While the criticism
is correct, we show here that (i) a singularity-free wormhole can actually be
obtained from Class I solution by performing a kind of Wick rotation on it,
resulting into what Brans listed as his independent Class II solution (ii) the
Class II solution has all the necessary properties of a regular wormhole in a
revised range -2<{\omega}<-3/2 and finally, (iii) naked black holes, as
described by Horowitz and Ross, are spacetimes where the tidal forces attain
their maxima above the black hole horizon. We show that in the non-singular
Class II spacetime this maxima is attained above the throat and thus can be
treated as a wormhole analogue. Some related issues are also addressed.Comment: 20 pages, 4 figure
Volume Integral Theorem for Exotic Matter
We answer an important question in general relativity about the volume
integral theorem for exotic matter by suggesting an exact integral quantifier
for matter violating Averaged Null Energy Condition (ANEC). It is checked
against some well known static, spherically symmetric traversable wormhole
solutions of general relativity with a sign reversed kinetic term minimally
coupled scalar field. The improved quantifier is consistent with the principle
that traversable wormholes can be supported by arbitrarily small quantities of
exotic matter.Comment: 7 page
Brans-Dicke wormholes in the Jordan and Einstein frames
We examine the possibility of static wormhole solutions in the vacuum
Brans-Dicke theory both in the original (Jordan) frame and in the conformally
rescaled (Einstein) frame. It turns out that, in the former frame, wormholes
exist only in a very narrow interval of the coupling parameter, viz.,
-3/2<omega<-4/3. It is shown that these wormholes are not traversable in
practice. In the latter frame, wormhole solutions do not exist at all unless
energy conditions are violated by hand.Comment: Minor errors corrected, uploaded for the benefit of the researcher
Magnetic structure of the Eu2+ moments in superconducting EuFe2(As1-xPx)2 with x = 0.19
The magnetic structure of the Eu2+ moments in the superconducting
EuFe2(As1-xPx)2 sample with x = 0.19 has been determined using neutron
scattering. We conclude that the Eu2+ moments are aligned along the c direction
below T_C = 19.0(1) K with an ordered moment of 6.6(2) mu_B in the
superconducting state. An impurity phase similar to the underdoped phase exists
within the bulk sample which orders antiferromagnetically below T_N = 17.0(2)
K. We found no indication of iron magnetic order, nor any incommensurate
magnetic order of the Eu2+ moments in the sample.Comment: Accepted for publication in Phys. Rev. B (regular article
Hydrogen Bond Dynamics Near A Micellar Surface: Origin of the Universal Slow Relaxation at Complex Aqueous Interfaces
The dynamics of hydrogen bonds among water molecules themselves and with the
polar head groups (PHG) at a micellar surface have been investigated by long
molecular dynamics simulations. The lifetime of the hydrogen bond between a PHG
and a water molecule is found to be much longer than that between any two water
molecules, and is likely to be a general feature of hydrophilic surfaces of
organized assemblies. Analyses of individual water trajectories suggest that
water molecules can remain bound to the micellar surface for more than a
hundred picosecond. The activation energy for such a transition from the bound
to a free state for the water molecules is estimated to be about 3.5kcal/mole.Comment: 12 pages. Phys. Rev. Lett. (Accepted) (2002
Gravitational Lensing by Wormholes
Gravitational lensing by traversable Lorentzian wormholes is a ew possibility
which is analyzed here in the strong field limit. Wormhole solutions are
considered in the Einstein minimally coupled theory and in the brane world
model. The observables in both the theories show significant differences from
those arising in the Schwarzschild black hole lensing. As a corollary, it
follows that wormholes with zero Keplerian mass exhibit lensing properties
which are qualitatively (though not quantitatively) the same as those of a
Schwarzschild black hole. Some special features of the considered solutions are
pointed out.Comment: 20 pages, no figure
Efficacy of surface error corrections to density functional theory calculations of vacancy formation energy in transition metals
We calculate properties like equilibrium lattice parameter, bulk modulus and
monovacancy formation energy for nickel (Ni), iron (Fe) and chromium (Cr) using
Kohn-Sham density functional theory (DFT). We compare relative performance of
local density approximation (LDA) and generalized gradient approximation (GGA)
for predicting such physical properties for these metals. We also make a
relative study between two different flavors of GGA exchange correlation
functional, namely, PW91 and PBE. These calculations show that there is a
discrepancy between DFT calculations and experimental data. In order to
understand this discrepancy in the calculation of vacancy formation energy, we
introduce a correction for the surface intrinsic error corresponding to an
exchange correlation functional using the scheme implemented by Mattsson et al.
[Phys. Rev. B 73, 195123 (2006)] and compare the effectiveness of the
correction scheme for Al and the 3d-transition metals.Comment: 29 pages, 3 figures, 5 tables, Published in J. Phys: Cond. Matt.
vol.22 (2010) 34550
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