15,202 research outputs found
He Scattering from Random Adsorbates, Disordered Compact Islands and Fractal Submonolayers: Intensity Manifestations of Surface Disorder
A theoretical study is made on He scattering from three fundamental classes
of disordered ad-layers: (a) Translationally random adsorbates, (b) disordered
compact islands and (c) fractal submonolayers. The implications of the results
to experimental studies of He scattering from disordered surfaces are
discussed, and a combined experimental-theoretical study is made for Ag
submonolayers on Pt(111). Some of the main theoretical findings are: (1)
Structural aspects of the calculated intensities from translationally random
clusters were found to be strongly correlated with those of individual
clusters. (2) Low intensity Bragg interference peaks appear even for scattering
from very small ad-islands, and contain information on the ad-island local
electron structure. (3) For fractal islands, just as for islands with a
different structure, the off-specular intensity depends on the parameters of
the He/Ag interaction, and does not follow a universal power law as previously
proposed in the literature. In the experimental-theoretical study of Ag on
Pt(111), we use first experimental He scattering data from low-coverage (single
adsorbate) systems to determine an empirical He/Ag-Pt potential of good
quality. Then, we carry out He scattering calculations for high coverage and
compare with experiments. The conclusions are that the actual experimental
phase corresponds to small compact Ag clusters of narrow size distribution,
translationally disordered on the surface.Comment: 36 double-spaced pages, 10 figures; accepted by J. Chem. Phys.,
scheduled to appear March 8. More info available at
http://www.fh.huji.ac.il/~dani
The Weyl-Lanczos Equations and the Lanczos Wave Equation in 4 Dimensions as Systems in Involution
Using the work by Bampi and Caviglia, we write the Weyl-Lanczos equations as
an exterior differential system. Using Janet-Riquier theory, we compute the
Cartan characters for all spacetimes with a diagonal metric and for the plane
wave spacetime since all spacetimes have a plane wave limit. We write the
Lanczos wave equation as an exterior differential system and, with assistance
from Janet-Riquier theory, we find that it forms a system in involution. This
result can be derived from the scalar wave equation itself. We compute its
Cartan characters and compare them with those of the Weyl-Lanczos equations.Comment: 18 pages, latex, no figures, references correcte
Antiferromagnetic order in CeCoIn5 oriented by spin-orbital coupling
An incommensurate spin density wave ( phase) confined inside the
superconducting state at high basal plane magnetic field is an unique property
of the heavy fermion metal CeCoIn. The neutron scattering experiments and
the theoretical studies point out that this state come out from the soft mode
condensation of magnetic resonance excitations. We show that the fixation of
direction of antiferromagnetic modulations by a magnetic field reported by
Gerber et al., Nat. Phys. {\bf 10}, 126 (2014) is explained by spin-orbit
coupling. This result, obtained on the basis of quite general phenomenological
arguments, is supported by the microscopic derivation of the
susceptibility dependence on the mutual orientation of the basal plane magnetic
field and the direction of modulation of spin polarization in a multi-band
metal.Comment: 7 pages plus 2 pages with 2 figure
Structure Determination of Disordered Metallic Sub-Monolayers by Helium Scattering: A Theoretical and Experimental Study
An approach based on He scattering is used to develop an atomic-level
structural model for an epitaxially grown disordered sub-monolayer of Ag on
Pt(111) at 38K. Quantum scattering calculations are used to fit structural
models to the measured angular intensity distribution of He atoms scattered
from this system. The structure obtained corresponds to narrowly size-dispersed
compact clusters with modest translational disorder, and not to fractals which
might be expected due to the low surface temperature. The clusters have up to
two layers in height, the lower one having few defects only. The relations
between specific features of the angular scattering distribution, and
properties such as the cluster sizes and shapes, the inter-cluster distance
distribution etc., are discussed. The results demonstrate the usefulness of He
scattering as a tool for unraveling new complex surface phases.Comment: 5 pages, 3 figures, to appear in Surf. Sci. Lett. Related papers
available at http://neon.cchem.berkeley.edu/~dani/He-papers.htm
A note on the topological order of noncommutative Hall fluids
We evaluate the ground state degeneracy of noncommutative Chern-Simons models
on the two-torus, a quantity that is interpreted as the "topological order" of
associated phases of Hall fluids. We define the noncommutative theory via
T-duality from an ordinary Chern-Simons model with non-abelian 't Hooft
magnetic fluxes. Motivated by this T-duality, we propose a discrete family of
noncommutative, non-abelian fluid models, arising as a natural generalization
of the standard noncommutative Chern-Simons effective models. We compute the
topological order for these universality classes, and comment on their possible
microscopic interpretation.Comment: 14 page
Conservation of the Anegada Iguana (Cyclura pinguis)
The long-term survival of the Anegada Iguana (Cyclura pinguis) is uncertain. The species is in danger of becoming extinct due to habitat destruction, competition with feral livestock, and the introduction of non-native mammalian predators. In an effort to save the Anegada Iguana, the IUCN Iguana Specialist Group and the British Virgin Islands National Parks Trust began a concerted conservation effort in 1997. They initiated a headstart program in order to bolster the wild population until many of the problems facing the iguanas can be minimized or removed. Headstarted iguanas were released back into the wild in October of 2003 and 2004. This paper briefly reviews the natural history of C. pinguis and presents some preliminary results from the ongoing long-term monitoring of the subadult iguanas reintroduced to the wild
Conservation of the Anegada Iguana (Cyclura pinguis)
The long-term survival of the Anegada Iguana (Cyclura pinguis) is uncertain. The species is in danger of becoming extinct due to habitat destruction, competition with feral livestock, and the introduction of non-native mammalian predators. In an effort to save the Anegada Iguana, the IUCN Iguana Specialist Group and the British Virgin Islands National Parks Trust began a concerted conservation effort in 1997. They initiated a headstart program in order to bolster the wild population until many of the problems facing the iguanas can be minimized or removed. Headstarted iguanas were released back into the wild in October of 2003 and 2004. This paper briefly reviews the natural history of C. pinguis and presents some preliminary results from the ongoing long-term monitoring of the subadult iguanas reintroduced to the wild
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