413 research outputs found
Vortex motion in a finite-size easy-plane ferromagnet and application to a nanodot
We study the motion of a non-planar vortex in a circular easy-plane
ferromagnet, which imitates a magnetic nanodot. Analysis was done using
numerical simulations and a new collective variable theory which includes the
coupling of Goldstone-like mode with the vortex center. Without magnetic field
the vortex follows a spiral orbit which we calculate. When a rotating in-plane
magnetic field is included, the vortex tends to a stable limit cycle which
exists in a significant range of field amplitude B and frequency for a
given system size L. For a fixed , the radius R of the orbital motion
is proportional to L while the orbital frequency varies as 1/L and is
significantly smaller than . Since the limit cycle is caused by the
interplay between the magnetization and the vortex motion, the internal mode is
essential in the collective variable theory which then gives the correct
estimate and dependency for the orbit radius . Using this
simple theory we indicate how an ac magnetic field can be used to control
vortices observed in real magnetic nanodots.Comment: 15 pages (RevTeX), 14 figures (eps
Low Temperature Static and Dynamic Behavior of the Two-Dimensional Easy-Axis Heisenberg Model
We apply the self-consistent harmonic approximation (SCHA) to study static
and dynamic properties of the two-dimensional classical Heisenberg model with
easy-axis anisotropy. The static properties obtained are magnetization and spin
wave energy as functions of temperature, and the critical temperature as a
function of the easy-axis anisotropy. We also calculate the dynamic correlation
functions using the SCHA renormalized spin wave energy. Our analytical results,
for both static properties and dynamic correlation functions, are compared to
numerical simulation data combining cluster-Monte Carlo algorithms and Spin
Dynamics. The comparison allows us to conclude that far below the transition
temperature, where the SCHA is valid, spin waves are responsible for all
relevant features observed in the numerical simulation data; topological
excitations do not seem to contribute appreciably. For temperatures closer to
the transition temperature, there are differences between the dynamic
correlation functions from SCHA theory and Spin Dynamics; these may be due to
the presence of domain walls and solitons.Comment: 12 pages, 14 figure
Comparação dos modelos digitais de elevação gerados com dados SRTM e cartas IBGE na escala 1:250.000 na região da Bacia do Camanducaia no Estado de São Paulo.
O estudo comparou os MDEs, os mapas de declividade e os mapas hipsomĂ©tricos produzidos pela SRTM com aqueles gerados pelas cartas do IBGE. A ĂĄrea estudada integra a bacia do Camanducaia, que limita-se como Estado de SĂŁo Paulo a leste e JaguariĂșna a oeste, abrangendo Holambra, JaguariĂșna, Santo AntĂŽnio de Posse, Pedreira, Amparo, Serra Negra, Monte Alegre do Sul, Socorro, Pinhalzinho e Pedra Bela
Vortices in the presence of a nonmagnetic atom impurity in 2D XY ferromagnets
Using a model of nonmagnetic impurity potential, we have examined the
behavior of planar vortex solutions in the classical two-dimensional XY
ferromagnets in the presence of a spin vacancy localized out of the vortex
core. Our results show that a spinless atom impurity gives rise to an effective
potential that repels the vortex structure.Comment: 6 pages, 2 figures, RevTex
Neutrino Masses and Lepton Flavour Violation in Thick Brane Scenarios
We address the issue of lepton flavour violation and neutrino masses in the
``fat-brane'' paradigm, where flavour changing processes are suppressed by
localising different fermion field wave-functions at different positions (in
the extra dimensions) in a thick brane. We study the consequences of
suppressing lepton number violating charged lepton decays within this scenario
for lepton masses and mixing angles. In particular, we find that charged lepton
mass matrices are constrained to be quasi-diagonal. We further consider whether
the same paradigm can be used to naturally explain small Dirac neutrino masses
by considering the existence of three right-handed neutrinos in the brane, and
discuss the requirements to obtain phenomenologically viable neutrino masses
and mixing angles. Finally, we examine models where neutrinos obtain a small
Majorana mass by breaking lepton number in a far away brane and show that, if
the fat-brane paradigm is the solution to the absence of lepton number
violating charged lepton decays, such models predict, in the absence of flavour
symmetries, that charged lepton flavour violation will be observed in the next
round of rare muon/tau decay experiments.Comment: 33 pages, 9 eps figure
Teor de carotenoides em nutricosméticos: anålise da adequação e qualidade do produto.
O objetivo deste trabalho foi verificar a adequação dos nutricosmĂ©ticos contendo carotenoides em sua formulação em relação aos teores de B-caroteno, luteĂna, licopeno e zeaxantina, considerando-se as quantidades declaradas pelos fabricantes. Dezenove nutricosmĂ©ticos foram adquiridos no comĂ©rcio varejista do municĂpio do Rio de Janeiro, em 2012. Duas metodologias de extração foram aplicadas, variando-se de acordo com o tipo de invĂłlucro (cĂĄpsula), veĂculos (excipientes) e carotenoides presentes. A quantificação e determinação do perfil de carotenoides nas amostras foram realizadas por cromatografia lĂquida de alta eficiĂȘncia com mĂ©todo validado e acreditado. Quatro amostras das 19 analisadas estavam dentro dos limites estabelecidos pelas Boas PrĂĄticas de Fabricação (90 a 110%). As demais amostras revelaram conteĂșdo inadequado de carotenoides e, consequentemente, falhas no controle de qualidade para a produção dos nutricosmĂ©ticos. Desta forma, esta pesquisa demonstra que este setor deve ser objeto de atenção especial da vigilĂąncia sanitĂĄria, com necessidade de estabelecer legislação especĂfica para regulamentar a fabricação, a rotulagem e a propaganda destes produtos
Comments on glueballinos (R0 particles) and R0 searches
We propose a search strategy for the light R0 (glueballino) particle
suggested by G.Farrar in connection with the light gluino scenario. The basic
idea is to moderate and stop the R0 particles and then observe their decay to
almost monochromatic pions - at an appropriate time delay relative to a primary
collision event, where a gluino jet, likely to fragment into the R0, was
produced. This technique is optimized at colliders and depends on qualitative
features of the R0 hadronic interactions which we discuss in detail.Comment: LaTeX, 28 page
Proteomic analysis of soybean leaves in a compatible and an incompatible interaction with Phakopsora pachyrhizi.
Asian soybean rust (ASR), which is incited by the fungus Phakopsora pachyrhizi, is considered one of the most aggressive diseases to the soybean culture. There are no commercial cultivars immune to the pathogen and the control measure currently used is the application of fungicides that harms the environment and increases production costs. For a better understanding of the host?s response to the pathogen at the molecular level, two soybean genotypes were analyzed (PI561356, resistant to ASR and Embrapa 48, susceptible) at 72 hours and 192 hours after inoculation with spores of P. pachyrhizi. Leaf protein profiles of the plants were compared by two-dimensional electrophoresis associated with mass spectrometry (MS). Twenty-two protein spots presented different levels when the two treatments were compared (inoculated vs. non-inoculated). From those, twelve proteins were identified by MS analysis. Some of them are involved in metabolic pathways related to plant defense against pathogens, as in the case of carbonic anhydrase, 1-deoxy-D-xylulose- 5-phosphate reductoisomerase, fructose-bisphosphate aldolase and glutamine synthetase. The possible biochemical-physiological meanings of our findings are discussed
On the Moduli Problem and Baryogenesis in Gauge-mediated SUSY Breaking Models
We investigate whether the Affleck-Dine mechanism can produce sufficient
baryon number of the universe in the gauge-mediated SUSY breaking models, while
evading the cosmological moduli problem by late-time entropy production. We
find that the Q-ball formation renders the scenario very difficult to work,
irrespective of the detail mechanism of the entropy production.Comment: 11 pages, RevTeX, 5 postscript figures include
- âŠ