1,435 research outputs found
Remarks on Charged Vortices in the Maxwell-Chern-Simons Model
We study vortex-like configuration in Maxwell-Chern-Simons Electrodynamics.
Attention is paid to the similarity it shares with the Nielsen-Olesen solutions
at large distances. A magnetic symmetry between a point-like and an
azimuthal-like current in this framework is also pointed out. Furthermore, we
address the issue of a neutral and spinless particle interacting with a charged
vortex, and obtain that the Aharonov-Casher-type phase depends upon mass and
distance parameters.Comment: New refs. added. Version accepted for publication in Phys. Lett.
On Dirac-like Monopoles in a Lorentz- and CPT-violating Electrodynamics
We study magnetic monopoles in a Lorentz- and CPT-odd electrodynamical
framework in (3+1) dimensions. This is the standard Maxwell model extended by
means of a Chern-Simons-like term, (
constant), which respects gauge invariance but violates both Lorentz and CPT
symmetries (as a consequence, duality is also lost). Our main interest concerns
the analysis of the model in the presence of Dirac monopoles, so that the
Bianchi identity no longer holds, which naively yields the non-conservation of
electric charge. Since gauge symmetry is respected, the issue of charge
conservation is more involved. Actually, the inconsistency may be circumvented,
if we assume that the appearance of a monopole induces an extra electric
current. The reduction of the model to (2+1) dimensions in the presence of both
the magnetic sources and Lorentz-violating terms is presented. There, a
quantization condition involving the scalar remnant of , say, the mass
parameter, is obtained. We also point out that the breaking of duality may be
associated with an asymmetry between electric and magnetic sources in this
background, so that the electromagnetic force experienced by a magnetic pole is
supplemented by an extra term proportional to , whenever compared to the
one acting on an electric charge.Comment: 10 pages, no figures, typed in te
How hole defects modify vortex dynamics in ferromagnetic nanodisks
Defects introduced in ferromagnetic nanodisks may deeply affect the structure
and dynamics of stable vortex-like magnetization. Here, analytical techniques
are used for studying, among other dynamical aspects, how a small cylindrical
cavity modify the oscillatory modes of the vortex. For instance, we have
realized that if the vortex is nucleated out from the hole its gyrotropic
frequencies are shifted below. Modifications become even more pronounced when
the vortex core is partially or completely captured by the hole. In these
cases, the gyrovector can be partially or completely suppressed, so that the
associated frequencies increase considerably, say, from some times to several
powers. Possible relevance of our results for understanding other aspects of
vortex dynamics in the presence of cavities and/or structural defects are also
discussed.Comment: 9 pages, 4 page
Desempenho de cultivares de arroz de terras altas sob plantio direto e convencional.
Para avaliar a viabilidade de uso do plantio direto em arroz (Oryza sativa L.) de terras altas, bem como o comportamento das novas cultivares nesse sistema de cultivo, experimentos foram conduzidos em Santa Helena de Goiás (GO), Brasil, em um Latossolo Vermelho-Escuro, de uso contÃnuo sob plantio direto há 14 anos. Foram testadas 14 cultivares de arroz de terras altas sob plantio direto e convencional em duas safras (1998/99 e 1999/2000), utilizando delineamento de blocos casualizados, com quatro repetições. As parcelas constituÃram-se de quatro linhas de 5 m, espaçadas de 0,4 m entre si. As variáveis avaliadas foram: produtividade de grãos, altura de plantas, florescimento, acamamento e incidência de doenças. Pelos resultados obtidos, verificaram-se altas produtividades de grãos das cultivares, as quais apresentam diferenças no desempenho em diferentes anos, porém semelhantes nos sistemas de plantio. Em condições de menor disponibilidade hÃdrica e na ausência de adubação na semeadura, o plantio direto proporciona rendimento de grãos igual ao plantio convencional
Graphene as an electronic membrane
Experiments are finally revealing intricate facts about graphene which go
beyond the ideal picture of relativistic Dirac fermions in pristine two
dimensional (2D) space, two years after its first isolation. While observations
of rippling added another dimension to the richness of the physics of graphene,
scanning single electron transistor images displayed prevalent charge
inhomogeneity. The importance of understanding these non-ideal aspects cannot
be overstated both from the fundamental research interest since graphene is a
unique arena for their interplay, and from the device applications interest
since the quality control is a key to applications. We investigate the membrane
aspect of graphene and its impact on the electronic properties. We show that
curvature generates spatially varying electrochemical potential. Further we
show that the charge inhomogeneity in turn stabilizes ripple formation.Comment: 6 pages, 11 figures. Updated version with new results about the
re-hybridization of the electronic orbitals due to rippling of the graphene
sheet. The re-hybridization adds the next-to-nearest neighbor hopping effect
discussed in the previous version. New reference to recent STM experiments
that give support to our theor
Predicted defect induced vortex core switching in thin magnetic nanodisks
We investigate the influence of artificial defects (small holes) inserted
into magnetic nanodisks on the vortex core dynamics. One and two holes
(antidots) are considered. In general, the core falls into the hole but, in
particular, we would like to remark an interesting phenomenon not yet observed,
which is the vortex core switching induced by the vortex-hole interactions. It
occurs for the case with only one hole and for very special conditions
involving the hole size and position as well as the disk size. Any small
deformation in the disk geometry such as the presence of a second antidot
changes completely the vortex dynamics and the vortex core eventually falls
into one of the defects. After trapped, the vortex center still oscillates with
a very high frequency and small amplitude around the defect center.Comment: 11pages, Revtex format, 17 figure
Influence of multi-impacts on GFRP composites laminates
The behaviour of Glass Fibre Reinforced Composites (GFRPs) under single and multi-impact events of the same total energy was analysed. Experimental tests were performed considering circular simple supported plates impacted on its centre. The analyses of the results issuing from load–time, load–displacement and energy–time curves have shown that the sole impact of 3 J is more detrimental for the plate, relative to the other cases of cumulative damage (1 J + 2 J and 1 J + 1 J + 1 J). A fine-tune analysis of damage evolution between subsequent impacts using a numerical procedure including a cohesive mixed-mode damage model was also performed. This analysis permits to verify the evolution of the projected delaminated area as well as the fracture process zone in the vicinity of delaminations. It was verified that a negligible evolution of damage occurs in the case of three consecutive impacts of the same energy. Additionally, it was concluded that the cumulative damage in the case of (1 J + 2 J) is inferior to the one propitiated by the sole impact of maximum energy (3 J)
Ganho genético em potencial produtivo do arroz irrigado no Rio Grande do Sul, após o lançamento da cultivar BR-IRGA 409.
Este trabalho teve como objetivo estimar os ganhos genéticos em rendimento de grãos nos últimos 30 anos, ou a partir do lançamento da cultivar BR-IRGA 409, no estado do Rio Grande do Sul, com base no desempenho de cultivares representativas lançadas pela pesquisa
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