15,003 research outputs found
Spin and exchange coupling for Ti embedded in a surface dipolar network
We have studied the spin and exchange coupling of Ti atoms on a
CuN/Cu(100) surface using density functional theory. We find that
individual Ti have a spin of 1.0 (i.e., 2 Bohr Magneton) on the CuN/Cu(100)
surface instead of spin-1/2 as found by Scanning Tunneling Microscope. We
suggest an explanation for this difference, a two-stage Kondo effect, which can
be verified by experiments. By calculating the exchange coupling for Ti dimers
on the CuN/Cu(100) surface, we find that the exchange coupling across a
`void' of 3.6\AA\ is antiferromagnetic, whereas indirect (superexchange)
coupling through a N atom is ferromagnetic. We confirm the existence of
superexchange interactions by varying the Ti-N angle in a model trimer
calculation. For a square lattice of Ti on CuN/Cu(100), we find a novel
spin striped phase
Results in Kalb-Ramond field localization and resonances on deformed branes
We make an analysis about several aspects of localization of the Kalb-Ramond
gauge field in a specific four dimensional AdS membrane embedded in a five
dimensional space-time. The membrane is generated from a deformation of the
potential and belongs to a new class of defect solutions. In
this context we find resonance structures in the analysis of massive modes. The
study of deformed defects is important because they contain internal structures
and these may have implications to the way the background space-time is
constructed and the way its curvature behaves. The main objective here is to
observe the contributions of the deformation procedure to the resonances and
the well known field localization methods.Comment: 6 pages, 7 figures, Latex with EPL macr
Orbital Magnetic Dipole Mode in Deformed Clusters: A Fully Microscopic Analysis
The orbital M1 collective mode predicted for deformed clusters in a schematic
model is studied in a self-consistent random-phase-approximation approach which
fully exploits the shell structure of the clusters. The microscopic mechanism
of the excitation is clarified and the close correlation with E2 mode
established. The study shows that the M1 strength of the mode is fragmented
over a large energy interval. In spite of that, the fraction remaining at low
energy, well below the overwhelming dipole plasmon resonance, is comparable to
the strength predicted in the schematic model. The importance of this result in
view of future experiments is stressed.Comment: 10 pages, 3 Postscript figures, uses revte
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
Agronomic Potential and Nutritive Value of Promising \u3ci\u3eLeucaena\u3c/i\u3e Species in the Yucatan Peninsula
Two experiments were carried out in order to evaluate the agronomic potential, the nutritive value and the tolerance to psyllid (Heteropsilla cubana) of nine Leucaena species. A randomized block design with four repetitions was used. There were significant (P\u3c 0.01) differences on dry matter production (i.e. leaf and twigs yield ). L. collinsii showed the most promising result, which could be related to its high psyllid tolerance. In a second experiment, the preference indices of Leucaena species was assessed with sixteen male pelibuey sheep in a cafeteria trial. There were significant (P\u3c 0.0001) differences among Leucaena species. L. esculenta paniculata was the species most preferred . There was no relationship between chemical composition (i.e. ADF, NDF, and polyphenols) and preference and psyllid tolerance
Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas
We discuss unusual aspects of symmetry that can happen due to entropic
effects in the context of multi-scalar field theories at finite temperature. We
present their consequences, in special, for the case of nonrelativistic models
of hard core spheres. We show that for nonrelativistic models phenomena like
inverse symmetry breaking and symmetry non-restoration cannot take place, but a
reentrant phase at high temperatures is shown to be possible for some region of
parameters. We then develop a model of interest in studies of Bose-Einstein
condensation in dilute atomic gases and discuss about its phase transition
patterns. In this application to a Bose-Einstein condensation model, however,
no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O.
Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One
reference was update
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