24,370 research outputs found
(2,2)-Formalism of General Relativity: An Exact Solution
I discuss the (2,2)-formalism of general relativity based on the
(2,2)-fibration of a generic 4-dimensional spacetime of the Lorentzian
signature. In this formalism general relativity is describable as a Yang-Mills
gauge theory defined on the (1+1)-dimensional base manifold, whose local gauge
symmetry is the group of the diffeomorphisms of the 2-dimensional fibre
manifold. After presenting the Einstein's field equations in this formalism, I
solve them for spherically symmetric case to obtain the Schwarzschild solution.
Then I discuss possible applications of this formalism.Comment: 2 figures included, IOP style file neede
Electronic Transport in the Oxygen Deficient Ferromagnetic Semiconducting TiO
TiO films were deposited on (100) Lanthanum aluminates
LaAlO substrates at a very low oxygen chamber pressure
mtorr employing a pulsed laser ablation deposition technique. In previous work,
it was established that the oxygen deficiency in these films induced
ferromagnetism. In this work it is demonstrated that this same oxygen
deficiency also gives rise to semiconductor titanium ion impurity donor energy
levels. Transport resistivity measurements in thin films of TiO
are presented as a function of temperature and magnetic field. Magneto- and
Hall- resistivity is explained in terms of electronic excitations from the
titanium ion donor levels into the conduction band.Comment: RevTeX4, Four pages, Four Figures in ^.eps forma
New Hamiltonian formalism and quasi-local conservation equations of general relativity
I describe the Einstein's gravitation of 3+1 dimensional spacetimes using the
(2,2) formalism without assuming isometries. In this formalism, quasi-local
energy, linear momentum, and angular momentum are identified from the four
Einstein's equations of the divergence-type, and are expressed geometrically in
terms of the area of a two-surface and a pair of null vector fields on that
surface. The associated quasi-local balance equations are spelled out, and the
corresponding fluxes are found to assume the canonical form of energy-momentum
flux as in standard field theories. The remaining non-divergence-type
Einstein's equations turn out to be the Hamilton's equations of motion, which
are derivable from the {\it non-vanishing} Hamiltonian by the variational
principle. The Hamilton's equations are the evolution equations along the
out-going null geodesic whose {\it affine} parameter serves as the time
function. In the asymptotic region of asymptotically flat spacetimes, it is
shown that the quasi-local quantities reduce to the Bondi energy, linear
momentum, and angular momentum, and the corresponding fluxes become the Bondi
fluxes. The quasi-local angular momentum turns out to be zero for any
two-surface in the flat Minkowski spacetime. I also present a candidate for
quasi-local {\it rotational} energy which agrees with the Carter's constant in
the asymptotic region of the Kerr spacetime. Finally, a simple relation between
energy-flux and angular momentum-flux of a generic gravitational radiation is
discussed, whose existence reflects the fact that energy-flux always
accompanies angular momentum-flux unless the flux is an s-wave.Comment: 36 pages, 3 figures, RevTex
Nano granular metallic Fe - oxygen deficient TiO composite films: A room temperature, highly carrier polarized magnetic semiconductor
Nano granular metallic iron (Fe) and titanium dioxide (TiO) were
co-deposited on (100) lanthanum aluminate (LaAlO) substrates in a low
oxygen chamber pressure using a pulsed laser ablation deposition (PLD)
technique. The co-deposition of Fe and TiO resulted in 10 nm
metallic Fe spherical grains suspended within a TiO matrix. The
films show ferromagnetic behavior with a saturation magnetization of 3100 Gauss
at room temperature. Our estimate of the saturation magnetization based on the
size and distribution of the Fe spheres agreed well with the measured value.
The film composite structure was characterized as p-type magnetic semiconductor
at 300 K with a carrier density of the order of . The
hole carriers were excited at the interface between the nano granular Fe and
TiO matrix similar to holes excited in the metal/n-type
semiconductor interface commonly observed in Metal-Oxide-Semiconductor (MOS)
devices. From the large anomalous Hall effect directly observed in these films
it follows that the holes at the interface were strongly spin polarized.
Structure and magneto transport properties suggested that these PLD films have
potential nano spintronics applications.Comment: 6 pages in Latex including 8 figure
Rotating Black Hole Entropy from Two Different Viewpoints
Using the brick-wall method, we study the entropy of Kerr-Newman black hole
from two different viewpoints, a rest observer at infinity and zero angular
momentum observer near horizon. We investigate this with scalar field in the
canonical quantization approach. An observer at infinity can take one of the
two possible frequency ranges; one is with positive frequencies only and the
other is with the whole range including negative frequencies. On the other
hand, a zero angular momentum observer near horizon can take positive
frequencies only. For the observer at infinity the superradiant modes appear in
either choice of the frequency ranges and the two results coincide. For the
zero angular momentum observer superradiant modes do not appear due to absence
of ergoregion. The resulting entropies from the two viewpoints turn out to be
the same.Comment: LaTeX 18 pages, 2 figures, Minor modifications in section 3(ZAMO
Controlling internal barrier in low loss BaTiO3 supercapacitors
Supercapacitor behavior has been reported in a number of oxides including reduced BaTiO3 ferroelectric ceramics. These so-called giant properties are however not easily controlled. We show here that the continuous coating of individual BaTiO3 grains by a silica shell in combination with spark plasma sintering is a way to process bulk composites having supercapacitor features with low dielectric losses and temperature stability. The silica shell acts both as an oxidation barrier during the processing and as a dielectric barrier in the final composite
Free Energy Approach to the Formation of an Icosahedral Structure during the Freezing of Gold Nanoclusters
The freezing of metal nanoclusters such as gold, silver, and copper exhibits
a novel structural evolution. The formation of the icosahedral (Ih) structure
is dominant despite its energetic metastability. This important phenomenon,
hitherto not understood, is studied by calculating free energies of gold
nanoclusters. The structural transition barriers have been determined by using
the umbrella sampling technique combined with molecular dynamics simulations.
Our calculations show that the formation of Ih gold nanoclusters is attributed
to the lower free energy barrier from the liquid to the Ih phases compared to
the barrier from the liquid to the face-centered-cubic crystal phases
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