18,665 research outputs found
Electron Transfer Reaction Through an Adsorbed Layer
We consider electron transfer from a redox to an electrode through and
adsorbed intermediate. The formalism is developed to cover all regimes of
coverage factor, from lone adsorbate to monolayer regime. The randomness in the
distribution of adsorbates is handled using coherent potential approximation.
We give current-overpotential profile for all coverage regimes. We explictly
analyse the low and high coverage regimes by supplementing with DOS profile for
adsorbate in both weakly coupled and strongly coupled sector. The prominence of
bonding and anti-bonding states in the strongly coupled adsorbates at low
coverage gives rise to saddle point behaviour in current-overpotential profile.
We were able to recover the marcus inverted region at low coverage and the
traditional direct electron transfer behaviour at high coverage
Graviton resonances on two-field thick branes
This work presents new results about the graviton massive spectrum in
two-field thick branes. Analyzing the massive spectra with a relative
probability method we have firstly showed the presence of resonance structures
and obtained a connection between the thickness of the defect and the lifetimes
of such resonances. We obtain another interesting results considering the
degenerate Bloch brane solutions. In these thick brane models, we have the
emergence of a splitting effect controlled by a degeneracy parameter. When the
degeneracy constant tends to a critical value, we have found massive resonances
to the gravitational field indicating the existence of modes highly coupled to
the brane. We also discussed the influence of the brane splitting effect over
the resonance lifetimes.Comment: 15 pages, 8 figure
Gravity localization on hybrid branes
This work deals with gravity localization on codimension-1 brane worlds
engendered by compacton-like kinks, the so-called hybrid branes. In such
scenarios, the thin brane behaviour is manifested when the extra dimension is
outside the compact domain, where the energy density is non-trivial, instead of
asymptotically as in the usual thick brane models. The zero mode is trapped in
the brane, as required. The massive modes, although are not localized in the
brane, have important phenomenological implications such as corrections to the
Newton's law. We study such corrections in the usual thick domain wall and in
the hybrid brane scenarios. By means of suitable numerical methods, we attain
the mass spectrum for the graviton and the corresponding wavefunctions. The
spectra possess the usual linearly increasing behaviour from the Kaluza-Klein
theories. Further, we show that the 4D gravitational force is slightly
increased at short distances. The first eigenstate contributes highly for the
correction to the Newton's law. The subsequent normalized solutions have
diminishing contributions. Moreover, we find out that the phenomenology of the
hybrid brane is not different from the usual thick domain wall. The use of
numerical techniques for solving the equations of the massive modes is useful
for matching possible phenomenological measurements in the gravitational law as
a probe to warped extra dimensions.Comment: 15 pages, 11 figure
Antisymmetric tensor propagator with spontaneous Lorentz violation
In this work, we study the spontaneous Lorentz symmetry breaking due to an
antisymmetric 2-tensor field in Minkowski spacetime. For a smooth quadratic
potential, the spectrum of the theory exhibits massless and massive
excitations. We show that the equations of motion for the free field obey some
constraints which lead to the massive mode be non-propagating at leading order.
Besides, there exists a massless mode in the theory which can be identified
with the usual Kalb-Ramond field, carrying only one on-shell degree of freedom.
The same conclusion holds when one analyses the pole structure of its Feynman
propagator. A new complete set of spin-type operators is found, which was the
requirement to evaluate the propagator of the Kalb-Ramond field modified by the
presence of a nonzero vacuum expectation value responsible for the Lorentz
violation.Comment: 13 pages. Some modifications to match published version in
EuroPhysics Letter
Finite element approximation of the -Laplacian
We study a~priori estimates for the Dirichlet problem of the
-Laplacian,
We show that the gradients of the finite element approximation with zero
boundary data converges with rate if the exponent is
-H\"{o}lder continuous. The error of the gradients is measured in the
so-called quasi-norm, i.e. we measure the -error of
Orbital magnetism in axially deformed sodium clusters: From scissors mode to dia-para magnetic anisotropy
Low-energy orbital magnetic dipole excitations, known as scissors mode (SM),
are studied in alkali metal clusters. Subsequent dynamic and static effects are
explored. The treatment is based on a self-consistent microscopic approach
using the jellium approximation for the ionic background and the Kohn-Sham mean
field for the electrons. The microscopic origin of SM and its main features
(structure of the mode in light and medium clusters, separation into low- and
high-energy plasmons, coupling high-energy M1 scissors and E2 quadrupole
plasmons, contributions of shape isomers, etc) are discussed. The scissors M1
strength acquires large values with increasing cluster size. The mode is
responsible for the van Vleck paramagnetism of spin-saturated clusters. Quantum
shell effects induce a fragile interplay between Langevin diamagnetism and van
Vleck paramagnetism and lead to a remarkable dia-para anisotropy in magnetic
susceptibility of particular light clusters. Finally, several routes for
observing the SM experimentally are discussed.Comment: 21 pages, 7 figure
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