43,990 research outputs found
Co-rich decagonal Al-Co-Ni: predicting structure, orientational order, and puckering
We apply systematic methods previously used by Mihalkovic et al. to predict
the structure of the `basic' Co-rich modification of the decagonal Al70 Co20
Ni10 layered quasicrystal, based on known lattice constants and previously
calculated pair potentials. The modelling is based on Penrose tile decoration
and uses Monte Carlo annealing to discover the dominant motifs, which are
converted into rules for another level of description. The result is a network
of edge-sharing large decagons on a binary tiling of edge 10.5 A. A detailed
analysis is given of the instability of a four-layer structure towards
-doubling and puckering of the atoms out of the layers, which is applied to
explain the (pentagonal) orientational order.Comment: IOP LaTex; 7 pp, 2 figures. In press, Phil. Mag. A (Proc. Intl. Conf.
on Quasicrystals 9, Ames Iowa, May 2005
Energy-based Structure Prediction for d(Al70Co20Ni10)
We use energy minimization principles to predict the structure of a decagonal
quasicrystal - d(AlCoNi) - in the Cobalt-rich phase. Monte Carlo methods are
then used to explore configurations while relaxation and molecular dynamics are
used to obtain a more realistic structure once a low energy configuration has
been found. We find five-fold symmetric decagons 12.8 A in diameter as the
characteristic formation of this composition, along with smaller
pseudo-five-fold symmetric clusters filling the spaces between the decagons. We
use our method to make comparisons with a recent experimental approximant
structure model from Sugiyama et al (2002).Comment: 10pp, 2 figure
Digging deep the oil world: corporate liability and environmental justice strategies
The impacts provoked by the expanding oil industry encompass environmental destruction, health impacts and violations of human rights. The increasing contamination jeopardizes safe conditions of life and destroys means of livelihood of vulnerable communities and of those relying on healthy ecosystems. Local communities, feeling that they are simply sacrificed to the oil industry, see themselves involved in social conflict. They are experiencing forms of environmental discrimination and might even face criminalisation of the protest when they stand up to defend their rights promoting the chilly effect on others who need and want to defend themselves and the environment. In fact, the number of lawsuits demanding justice for environmental, social, economical and cultural damages provoked by oil companies are increasing as well as their media visibility. Yet most outcomes are not satisfactory in tackling impacted communities claims for justice. This paper describes the most recent trends regarding oil corporations’ responsibilities and use of procedural justice by civil society through the review of emblematic legal cases
Nonlinear alternating current responses of graded materials
When a composite of nonlinear particles suspended in a host medium is
subjected to a sinusoidal electric field, the electrical response in the
composite will generally consist of alternating current (AC) fields at
frequencies of higher-order harmonics. The situation becomes more interesting
when the suspended particles are graded, with a spatial variation in the
dielectric properties. The local electric field inside the graded particles can
be calculated by the differential effective dipole approximation, which agrees
very well with a first-principles approach. In this work, a nonlinear
differential effective dipole approximation and a perturbation expansion method
have been employed to investigate the effect of gradation on the nonlinear AC
responses of these composites. The results showed that the fundamental and
third-harmonic AC responses are sensitive to the dielectric-constant and/or
nonlinear-susceptibility gradation profiles within the particles. Thus, by
measuring the AC responses of the graded composites, it is possible to perform
a real-time monitoring of the fabrication process of the gradation profiles
within the graded particles.Comment: 18 pages, 4 figure
Radiative Neutrino Mass, Dark Matter and Leptogenesis
We propose an extension of the standard model, in which neutrinos are Dirac
particles and their tiny masses originate from a one-loop radiative diagram.
The new fields required by the neutrino mass-generation also accommodate the
explanation for the matter-antimatter asymmetry and dark matter in the
universe.Comment: 4 pages, 3 figures. Revised version with improved model. Accepted by
PR
Neutrino masses, leptogenesis and dark matter in hybrid seesaw
We suggest a hybrid seesaw model where relatively ``light''right-handed
neutrinos give no contribution to the neutrino mass matrix due to a special
symmetry. This allows their Yukawa couplings to the standard model particles to
be relatively strong, so that the standard model Higgs boson can decay
dominantly to a left and a right-handed neutrino, leaving another stable
right-handed neutrino as cold dark matter. In our model neutrino masses arise
via the type-II seesaw mechanism, the Higgs triplet scalars being also
responsible for the generation of the matter-antimatter asymmetry via the
leptogenesis mechanism.Comment: 4 page
- …