9,438 research outputs found
Spin g-factor due to electronic interactions in graphene
The gyromagnetic factor is an important physical quantity relating the
magnetic-dipole moment of a particle to its spin. The electron spin g-factor in
vacuo is one of the best model-based theoretical predictions ever made, showing
agreement with the measured value up to ten parts per trillion. However, for
electrons in a material the g-factor is modified with respect to its value in
vacuo because of environment interactions. Here, we show how interaction
effects lead to the spin g-factor correction in graphene by considering the
full electromagnetic interaction in the framework of pseudo-QED. We compare our
theoretical prediction with experiments performed on graphene deposited on SiO2
and SiC, and we find a very good agreement between them.Comment: Improved version of the manuscript; valley g-factor part has been
remove
Modulated phases and devil's staircases in a layered mean-field version of the ANNNI model
We investigate the phase diagram of a spin- Ising model on a cubic
lattice, with competing interactions between nearest and next-nearest neighbors
along an axial direction, and fully connected spins on the sites of each
perpendicular layer. The problem is formulated in terms of a set of
noninteracting Ising chains in a position-dependent field. At low temperatures,
as in the standard mean-feild version of the Axial-Next-Nearest-Neighbor Ising
(ANNNI) model, there are many distinct spatially commensurate phases that
spring from a multiphase point of infinitely degenerate ground states. As
temperature increases, we confirm the existence of a branching mechanism
associated with the onset of higher-order commensurate phases. We check that
the ferromagnetic phase undergoes a first-order transition to the modulated
phases. Depending on a parameter of competition, the wave number of the striped
patterns locks in rational values, giving rise to a devil's staircase. We
numerically calculate the Hausdorff dimension associated with these
fractal structures, and show that increases with temperature but seems
to reach a limiting value smaller than .Comment: 17 pages, 6 figure
Improving Memory Hierarchy Utilisation for Stencil Computations on Multicore Machines
Although modern supercomputers are composed of multicore machines, one can
find scientists that still execute their legacy applications which were
developed to monocore cluster where memory hierarchy is dedicated to a sole
core. The main objective of this paper is to propose and evaluate an algorithm
that identify an efficient blocksize to be applied on MPI stencil computations
on multicore machines. Under the light of an extensive experimental analysis,
this work shows the benefits of identifying blocksizes that will dividing data
on the various cores and suggest a methodology that explore the memory
hierarchy available in modern machines
Unitarity of theories containing fractional powers of the d'Alembertian operator
We examine the unitarity of a class of generalized Maxwell U(1) gauge
theories in (2+1) D containing the pseudodifferential operator
, for . We show that only Quantum
Electrodynamics (QED) and its generalization known as Pseudo Quantum
Electrodynamics (PQED), for which and , respectively,
satisfy unitarity. The latter plays an important role in the description of the
electromagnetic interactions of charged particles confined to a plane, such as
in graphene or in hetero-junctions displaying the quantum Hall effect.Comment: 6 pages, no figure
Interaction Induced Quantum Valley Hall Effect in Graphene
We use Pseudo Quantum Electrodynamics (PQED) in order to describe the full
electromagnetic interaction of the p-electrons of graphene in a consistent 2D
formulation. We first consider the effect of this interaction in the vacuum
polarization tensor or, equivalently, in the current correlator. This allows us
to obtain the dc conductivity after a smooth zero-frequency limit is taken in
Kubo's formula.Thereby, we obtain the usual expression for the minimal
conductivity plus corrections due to the interaction that bring it closer to
the experimental value. We then predict the onset of an interaction-driven
spontaneous Quantum Valley Hall effect (QVHE) below a critical temperature of
the order of K. The transverse (Hall) valley conductivity is evaluated
exactly and shown to coincide with the one in the usual Quantum Hall effect.
Finally, by considering the effects of PQED, we show that the electron
self-energy is such that a set of P- and T- symmetric gapped electron energy
eigenstates are dynamically generated, in association with the QVHE.Comment: 5 pages + supplemental materia
Importância da avaliação microbiológica na qualidade e segurança dos alimentos.
Abordagem técnológica. Abordagem metodológica. Relevância econômica, social e ambiental. Referências bibliográficasbitstream/CNPAB-2010/27380/1/doc120.pd
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