593 research outputs found
Structural determination of bilayer graphene on SiC(0001) using synchrotron radiation photoelectron diffraction
In recent years there has been growing interest in the electronic properties of 'few layer' graphene films. Twisted layers, different stacking and register with the substrate result in remarkable unconventional couplings. These distinctive electronic behaviours have been attributed to structural differences, even if only a few structural determinations are available. Here we report the results of a structural study of bilayer graphene on the Si-terminated SiC(0001) surface, investigated using synchrotron radiation-based photoelectron diffraction and complemented by angle-resolved photoemission mapping of the electronic valence bands. Photoelectron diffraction angular distributions of the graphene C 1s component have been measured at different kinetic energies and compared with the results of multiple scattering simulations for model structures. The results confirm that bilayer graphene on SiC(0001) has a layer spacing of 3.48 Å and an AB (Bernal) stacking, with a distance between the C buffer layer and the first graphene layer of 3.24 Å. Our work generalises the use of a versatile and precise diffraction method capable to shed light on the structure of low-dimensional materials
The oldest Camelidae (Mammalia, Artiodactyla) of Africa : new finds from the Mio-Pliocene boundary,Chad
Un fragment de mandibule et deux métapodes complets provenant du secteur fossilifère de Kossom Bougoudi
(KB3 et KB26), Nord Tchad sont décrits. Une étude comparative permet d’attribuer les spécimens à Paracamelus gigas.
Le degré évolutif des spécimens est compatible avec l’âge biochronologique des sites KB, proche de la limite
Mio-Pliocène (ca 5 Ma). Les témoins les plus anciens du genre sont connus dans le Miocène supérieur d’Asie et d’Europe.
Les restes tchadiens sont donc les plus anciens du continent attribués au genre
Potts models in the continuum. Uniqueness and exponential decay in the restricted ensembles
In this paper we study a continuum version of the Potts model. Particles are
points in R^d, with a spin which may take S possible values, S being at least
3. Particles with different spins repel each other via a Kac pair potential. In
mean field, for any inverse temperature there is a value of the chemical
potential at which S+1 distinct phases coexist. For each mean field pure phase,
we introduce a restricted ensemble which is defined so that the empirical
particles densities are close to the mean field values. Then, in the spirit of
the Dobrushin Shlosman theory, we get uniqueness and exponential decay of
correlations when the range of the interaction is large enough. In a second
paper, we will use such a result to implement the Pirogov-Sinai scheme proving
coexistence of S+1 extremal DLR measures.Comment: 72 pages, 1 figur
Tooth serration morphologies in the genus Machimosaurus (Crocodylomorpha, Thalattosuchia) from the Late Jurassic of Europe
© 2014 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. The attached file is the published version of the article
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New Material of the Earliest Hominid from the Upper Miocene of Chad
Anthropolog
Coexistence of ordered and disordered phases in Potts models in the continuum
This is the second of two papers on a continuum version of the Potts model,
where particles are points in , , with a spin which may
take possible values. Particles with different spins repel each other
via a Kac pair potential of range \ga^{-1}, \ga>0. In this paper we prove
phase transition, namely we prove that if the scaling parameter of the Kac
potential is suitably small, given any temperature there is a value of the
chemical potential such that at the given temperature and chemical potential
there exist mutually distinct DLR measures.Comment: 57 pages, 1 figur
SNO+: predictions from standard solar models and spin flavour precession
Time variability of the solar neutrino flux especially in the low and
intermediate energy sector remains an open question and, if it exists, it is
likely to be originated from the magnetic moment transition from active to
light sterile neutrinos at times of intense solar activity and magnetic field.
We examine the prospects for the SNO+ experiment to address this important
issue and to distinguish between the two classes of solar models which are
currently identified as corresponding to a high (SSM I) and a low (SSM II)
heavy element abundance. We also evaluate the predictions from these two models
for the Chlorine experiment event rate in the standard LMA and LMA+Spin Flavour
Precession (SFP) scenarios. It is found that after three years of SNO+ data
taking, the pep flux measurement will be able to discriminate between the
standard LMA and LMA+SFP scenarios, independently of which is the correct solar
model. If the LMA rate is measured, SFP with for the resonant
can be excluded at more than . A low rate would
signal new physics, excluding all the 90% allowed range of the standard LMA
solution at 3, and a time variability would be a strong signature of
the SFP model. The CNO fluxes are the ones for which the two SSM predictions
exhibit the largest differences, so their measurement at SNO+ will be important
to favour one or the other. The distinction will be clearer after LMA or SFP
are confirmed with pep, but still, a CNO measurement at the level of SSM I/LMA
will disfavour SSM II at about . We conclude that consistency between
future pep and CNO flux measurements at SNO+ and Chlorine would either favour
an LMA+SFP scenario or favour SSM II over SSM I.Comment: 20 pages. Sections 1 and 2 extended, section 4.4 added, references
added and updated. Final version to be published in JHE
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