2,054 research outputs found
Covariant EBK quantization of the electromagnetic two-body problem
We discuss a method to transform the covariant Fokker action into an implicit
two-degree-of-freedom Hamiltonian for the electromagnetic two-body problem with
arbitrary masses. This dynamical system appeared 100 years ago and it was
popularized in the 1940's by the still incomplete Wheeler and Feynman program
to quantize it as a means to overcome the divergencies of perturbative QED. Our
finite-dimensional implicit Hamiltonian is closed and involves no series
expansions. The Hamiltonian formalism is then used to motivate an EBK
quantization based on the classical trajectories with a non-perturbative
formula that predicts energies free of infinities.Comment: 21 page
Optical Dispersion In Annealed Thin Films of S-doped a-Si:H Alloys
S-doped amorphous hydrogenated silicon (a-Si,S:H) thin films were prepared by conventional PECVD method on corning glass substrates. The prepared thin films were subsequently annealed in vacuum (~ 2 × 10 – 6 Torr) in the temperature range from 100 °C to 500 °C. The annealing effects at room temperature were examined by means of optical transmission spectra of the films in the wavelength range 300-1100 nm. Dispersion in optical constants such as transmittance, bandgap and refractive index were observed. Tailoring in optical constants was observed with respect to doping concentrations as well as the annealing temperatures.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3097
Strengthening the integration of midwifery in health systems; a leader-to-leader collaboration
Barriers and facilitators for quality midwifery care exist on different levels in the health systems. After decades of challenges and varied degrees of success, a stakeholder leader-to-leader collaboration could provide added value through knowledge sharing on how to integrate the midwifery cadre into an existing health system. Initiated by The Midwifery Society of Nepal, Dalarna University Sweden and MAMTA - Health Institute for Mother and Child India, a research network focusing midwifery has been formed. The background, purpose and activities of this network has been described in this News and Events paper
Interior Weyl-type Solutions of the Einstein-Maxwell Field Equations
Static solutions of the electro-gravitational field equations exhibiting a
functional relationship between the electric and gravitational potentials are
studied. General results for these metrics are presented which extend previous
work of Majumdar. In particular, it is shown that for any solution of the field
equations exhibiting such a Weyl-type relationship, there exists a relationship
between the matter density, the electric field density and the charge density.
It is also found that the Majumdar condition can hold for a bounded perfect
fluid only if the matter pressure vanishes (that is, charged dust). By
restricting to spherically symmetric distributions of charged matter, a number
of exact solutions are presented in closed form which generalise the
Schwarzschild interior solution. Some of these solutions exhibit functional
relations between the electric and gravitational potentials different to the
quadratic one of Weyl. All the non-dust solutions are well-behaved and, by
matching them to the Reissner-Nordstr\"{o}m solution, all of the constants of
integration are identified in terms of the total mass, total charge and radius
of the source. This is done in detail for a number of specific examples. These
are also shown to satisfy the weak and strong energy conditions and many other
regularity and energy conditions that may be required of any physically
reasonable matter distribution.Comment: 21 pages, RevTex, to appear in General Relativity and Gravitatio
Perfectly Translating Lattices on a Cylinder
We perform molecular dynamics simulations on an interacting electron gas
confined to a cylindrical surface and subject to a radial magnetic field and
the field of the positive background. In order to study the system at lowest
energy states that still carry a current, initial configurations are obtained
by a special quenching procedure. We observe the formation of a steady state in
which the entire electron-lattice cycles with a common uniform velocity.
Certain runs show an intermediate instability leading to lattice
rearrangements. A Hall resistance can be defined and depends linearly on the
magnetic field with an anomalous coefficient reflecting the manybody
contributions peculiar to two dimensions.Comment: 13 pages, 5 figure
Trapping of a random walk by diffusing traps
We present a systematic analytical approach to the trapping of a random walk
by a finite density rho of diffusing traps in arbitrary dimension d. We confirm
the phenomenologically predicted e^{-c_d rho t^{d/2}} time decay of the
survival probability, and compute the dimension dependent constant c_d to
leading order within an eps=2-d expansion.Comment: 16 pages, to appear in J. Phys.
The Tolman VII solution, trapped null orbits and w - modes
The Tolman VII solution is an exact static spherically symmetric perfect
fluid solution of Einstein's equations that exhibits a surprisingly good
approximation to a neutron star. We show that this solution exhibits trapped
null orbits in a causal region even for a tenuity (total radius to mass ratio)
. In this region the dynamical part of the potential for axial w - modes
dominates over the centrifugal part.Comment: 5 pages revtex. 10 figures png. Further information at
http://grtensor.phy.queensu.ca/tolmanvii
Matter-field theory of the Casimir force
A matter-field theory of the Casimir force is formulated in which the
electromagnetic field and collective modes of dielectric media are treated on
an equal footing. In our theory, the Casimir force is attributed to zero-point
energies of the combined matter-field modes. We analyze why some of the
existing theories favor the interpretation of the Casimir force as originating
from zero-point energies of the electromagnetic field and others from those of
the matter.Comment: 12pages, 1 Postscript figur
Structure optimization in an off-lattice protein model
We study an off-lattice protein toy model with two species of monomers
interacting through modified Lennard-Jones interactions. Low energy
configurations are optimized using the pruned-enriched-Rosenbluth method
(PERM), hitherto employed to native state searches only for off lattice models.
For 2 dimensions we found states with lower energy than previously proposed
putative ground states, for all chain lengths . This indicates that
PERM has the potential to produce native states also for more realistic protein
models. For , where no published ground states exist, we present some
putative lowest energy states for future comparison with other methods.Comment: 4 pages, 2 figure
Radiative Corrections to the Casimir Energy
The lowest radiative correction to the Casimir energy density between two
parallel plates is calculated using effective field theory. Since the
correlators of the electromagnetic field diverge near the plates, the
regularized energy density is also divergent. However, the regularized integral
of the energy density is finite and varies with the plate separation L as
1/L^7. This apparently paradoxical situation is analyzed in an equivalent, but
more transparent theory of a massless scalar field in 1+1 dimensions confined
to a line element of length L and satisfying Dirichlet boundary conditions.Comment: 7 pages, Late
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