23,558 research outputs found
Mean-field analysis of the majority-vote model broken-ergodicity steady state
We study analytically a variant of the one-dimensional majority-vote model in
which the individual retains its opinion in case there is a tie among the
neighbors' opinions. The individuals are fixed in the sites of a ring of size
and can interact with their nearest neighbors only. The interesting feature
of this model is that it exhibits an infinity of spatially heterogeneous
absorbing configurations for whose statistical properties we
probe analytically using a mean-field framework based on the decomposition of
the -site joint probability distribution into the -contiguous-site joint
distributions, the so-called -site approximation. To describe the
broken-ergodicity steady state of the model we solve analytically the
mean-field dynamic equations for arbitrary time in the cases n=3 and 4. The
asymptotic limit reveals the mapping between the statistical
properties of the random initial configurations and those of the final
absorbing configurations. For the pair approximation () we derive that
mapping using a trick that avoids solving the full dynamics. Most remarkably,
we find that the predictions of the 4-site approximation reduce to those of the
3-site in the case of expectations involving three contiguous sites. In
addition, those expectations fit the Monte Carlo data perfectly and so we
conjecture that they are in fact the exact expectations for the one-dimensional
majority-vote model
Graphene-based spin-pumping transistor
We demonstrate with a fully quantum-mechanical approach that graphene can
function as gate-controllable transistors for pumped spin currents, i.e., a
stream of angular momentum induced by the precession of adjacent
magnetizations, which exists in the absence of net charge currents.
Furthermore, we propose as a proof of concept how these spin currents can be
modulated by an electrostatic gate. Because our proposal involves nano-sized
systems that function with very high speeds and in the absence of any applied
bias, it is potentially useful for the development of transistors capable of
combining large processing speeds, enhanced integration and extremely low power
consumption
Graphene as a non-magnetic spin-current lens
In spintronics, the ability to transport magnetic information often depends
on the existence of a spin current traveling between two different magnetic
objects acting as source and probe. A large fraction of this information never
reaches the probe and is lost because the spin current tends to travel
omni-directionally. We propose that a curved boundary between a gated and a
non-gated region within graphene acts as an ideal lens for spin currents
despite being entirely of non-magnetic nature. We show as a proof of concept
that such lenses can be utilized to redirect the spin current that travels away
from a source onto a focus region where a magnetic probe is located, saving a
considerable fraction of the magnetic information that would be otherwise lost.Comment: 9 pages, 3 figure
Dynamic RKKY interaction in graphene
The growing interest in carbon-based spintronics has stimulated a number of
recent theoretical studies on the RKKY interaction in graphene, based on which
the energetically favourable alignment between magnetic moments embedded in
this material can be calculated. The general consensus is that the strength of
the RKKY interaction in graphene decays as 1/D3 or faster, where D is the
separation between magnetic moments. Such an unusually fast decay for a
2-dimensional system suggests that the RKKY interaction may be too short ranged
to be experimentally observed in graphene. Here we show in a mathematically
transparent form that a far more long ranged interaction arises when the
magnetic moments are taken out of their equilibrium positions and set in
motion. We not only show that this dynamic version of the RKKY interaction in
graphene decays far more slowly but also propose how it can be observed with
currently available experimental methods.Comment: 7 pages, 2 figures, submitte
Generalized Miura Transformations, Two-Boson KP Hierarchies and their Reduction to KDV Hierarchies
Bracket preserving gauge equivalence is established between several two-boson
generated KP type of hierarchies. These KP hierarchies reduce under symplectic
reduction (via Dirac constraints) to KdV, mKdV and Schwarzian KdV hierarchies.
Under this reduction the gauge equivalence is taking form of the conventional
Miura maps between the above KdV type of hierarchies.Comment: 12 pgs., LaTeX, IFT-P/011/93, UICHEP-TH/93-
Dynamic RKKY interaction between magnetic moments in graphene nanoribbons
Graphene has been identified as a promising material with numerous
applications, particularly in spintronics. In this paper we investigate the
peculiar features of spin excitations of magnetic units deposited on graphene
nanoribbons and how they can couple through a dynamical interaction mediated by
spin currents. We examine in detail the spin lifetimes and identify a pattern
caused by vanishing density of states sites in pristine ribbons with armchair
borders. Impurities located on these sites become practically invisible to the
interaction, but can be made accessible by a gate voltage or doping. We also
demonstrate that the coupling between impurities can be turned on or off using
this characteristic, which may be used to control the transfer of information
in transistor-like devices.Comment: 10 pages, 10 figure
Distribuição espacial da comunidade de insetos-praga em soja cultivada em sistema silviagrÃcola
A amostragem é uma etapa fundamental do manejo integrado de pragas, pois permiti avaliar quando as pragas atingem seus nÃveis de controle. Considerando que a integração de espécies vegetais pode influenciar na distribuição espacial dos insetos, objetivou-se avaliar se o método de caminhamento aleatório na cultura da soja em monocultivo pode ser utilizado em soja cultivada em sistemas silviagrÃcolas. Avaliou-se 12 parcelas de 2 ha cada contendo três ranks de três linhas de eucalipto (árvores com 2,5 anos) espaçados a cada 30m, sendo que nos espaços entre ranks foi cultivada a soja. As avaliações foram realizadas semanalmente, avaliando-se três pontos (1m da cultura) por parcela pelo método do pano de batida. As coordenadas dos pontos de amostragem foram: i: rente à face sul dos ranks; ii. entre os ranks (aproximadamente 15m dos ranks) e, iii. rente à face norte dos ranks. Durante o cultivo da soja, a projeção da sombra do eucalipto estava na face sul. Observou-se que entre os lepidópteros, a presença de Anticarsia gemmatalis, espécies de Plusinae e de Spodoptera spp. foi significativamente maior entre os rankse Heliothinae não diferiu significativamente entre os pontos de amostragem. No entanto, ao avaliar a porcentagem de desfolha, não houve diferença significativa entre os locais. Ao avaliar a população de percevejos, constatou-se que Euschistus heros preferiu significativamente plantas localizadas na face sul dos ranks. Entretanto, Dichelops spp. preferiu significativamente plantas localizadas na face norte dos ranks. Portanto, tornar-se importante em sistemas silviagrÃcolas, a priorização de amostragens rentes as laterais dos ranks devido à diferença na distribuição espacial de espécies de percevejos em função da projeção da sombra proporcionada pelo componente florestal e por não haver diferença espacial significativa na desfolha provocada pelos lepidópteros
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