6,188 research outputs found
Temperature dependence of the coercive field in single-domain particle systems
The magnetic properties of Cu97Co3 and Cu90Co10 granular alloys were measured
over a wide temperature range (2 to 300K). The measurements show an unusual
temperature dependence of the coercive field. A generalized model is proposed
and explains well the experimental behavior over a wide temperature range. The
coexistence of blocked and unblocked particles for a given temperature rises
difficulties that are solved here by introducing a temperature dependent
blocking temperature. An empirical factor gamma arise from the model and is
directly related to the particle interactions. The proposed generalized model
describes well the experimental results and can be applied to other
single-domain particle system.Comment: 7 pages, 8 figures, revised version, accepted to Physical Review B on
29/04/200
Bistability, softening, and quenching of magnetic moments in Ni-filled carbon nanotubes
The authors apply first-principles calculations to investigate the interplay
between structural, electronic, and magnetic properties of nanostructures
composed of narrow nanotubes filled with metallic nanowires. The focus is on
the structural and magnetic responses of Ni-filled nanotubes upon radial
compression. Interestingly, metastable flattened structures are identified, in
which radially deformed nanotubes are stabilized by the interactions with the
encapsulated wire. Moreover, our results indicate a quenching of the magnetic
moment of the wire upon compression, as a result of the transfer of charge from
the to the orbitals of the atoms in the wire.Comment: 4 pages, 4 figure
Transfer reactions and the dispersive optical-model
The dispersive optical-model is applied to transfer reactions. A systematic
study of reactions on closed-shell nuclei using the finite-range
adiabatic reaction model is performed at several beam energies and results are
compared to data as well as to predictions using a standard global
optical-potential. Overall, we find that the dispersive optical-model is able
to describe the angular distributions as well as or better than the global
parameterization. In addition, it also constrains the overlap function.
Spectroscopic factors extracted using the dispersive optical-model are
generally lower than those using standard parameters, exhibit a reduced
dependence on beam energy, and are more in line with results obtained from
measurements.Comment: Phys. Rev. C 84, 044611 (2011
Fluctuations and oscillations in a simple epidemic model
We show that the simplest stochastic epidemiological models with spatial
correlations exhibit two types of oscillatory behaviour in the endemic phase.
In a large parameter range, the oscillations are due to resonant amplification
of stochastic fluctuations, a general mechanism first reported for
predator-prey dynamics. In a narrow range of parameters that includes many
infectious diseases which confer long lasting immunity the oscillations persist
for infinite populations. This effect is apparent in simulations of the
stochastic process in systems of variable size, and can be understood from the
phase diagram of the deterministic pair approximation equations. The two
mechanisms combined play a central role in explaining the ubiquity of
oscillatory behaviour in real data and in simulation results of epidemic and
other related models.Comment: acknowledgments added; a typo in the discussion that follows Eq. (3)
is corrected
Extração de fósforo por Mehlich 1 e resina de troca iônica em solos fertilizados com torta de filtro.
Parâmetros de qualidade de frutos de novos hÃbridos de abacaxizeiros desenvolvidos pela Embrapa Mandioca e Fruticultura.
O fruto do abacaxizeiro é bastante apreciado e apresenta grande aceitação no mercado mundial em decorrência de suas caracterÃsticas sensoriais e nutricionais. O programa de melhoramento genético do abacaxizeiro da Embrapa Mandioca e Fruticultura desenvolve novos hÃbridos para atender à s expectativas deste mercado
Rendimento de grãos e fatores de produção de trigo em função da ocorrência de precipitação pluviométrica na fase reprodutiva.
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