18,112 research outputs found
Transport properties of a two impurity system: a theoretical approach
A system of two interacting cobalt atoms, at varying distances, was studied
in a recent scanning tunneling microscope experiment by Bork et. al.[Nature
Phys. 7, 901 (2011)]. We propose a microscopic model that explains, for all
experimentally analyzed interatomic distances, the physics observed in these
experiments. Our proposal is based on the two-impurity Anderson model, with the
inclusion of a two-path geometry for charge transport. This many-body system is
treated in the finite-U slave boson mean-field approximation and the
logarithmic-discretization embedded-cluster approximation. We physically
characterize the different charge transport regimes of this system at various
interatomic distances and show that, as in the experiments, the features
observed in the transport properties depend on the presence of two impurities
but also on the existence of two conducting channels for electron transport. We
interpret the splitting observed in the conductance as the result of the
hybridization of the two Kondo resonances associated with each impurity.Comment: 5 pages, 5 figure
Probability distribution of the order parameter in the directed percolation universality class
The probability distributions of the order parameter for two models in the
directed percolation universality class were evaluated. Monte Carlo simulations
have been performed for the one-dimensional generalized contact process and the
Domany-Kinzel cellular automaton. In both cases, the density of active sites
was chosen as the order parameter. The criticality of those models was obtained
by solely using the corresponding probability distribution function. It has
been shown that the present method, which has been successfully employed in
treating equilibrium systems, is indeed also useful in the study of
nonequilibrium phase transitions.Comment: 6 pages, 4 figure
Desempenho de madeira de grevÃlea revestida com verniz, tinta e stain exposta a intemperismo natural.
Amostras de madeira de grevÃlea foram revestidas com verniz, tinta e stain adquiridos no mercado nacional e expostas a intemperismo natural durante 45 dias. Após esse perÃodo, o desempenho do revestimento foi avaliado quanto ao aparecimento de fungos, aspecto visual do recobrimento e à aderência do filme. Nove produtos foram usados para o recobrimento das amostras e um conjunto sem tratamento também foi exposto à s mesmas condições. Os filmes de acabamento tiveram uma boa adesão à madeira de grevÃlea tanto antes como após o intemperismo natural. O desenvolvimento de fungos foi inibido em relação à s amostras sem tratamento, mas apenas as amostras revestidas com Tinta a Óleo, Stain cor branca e o Impregnante GT impediram completamente o surgimento de fungos em 100 % das amostras.EBRAMEM
A new investigation of the binary HD 48099
With an orbital period of about 3.078 days, the double-lined spectroscopic
binary HD 48099 is, still now, the only short-period O+O system known in the
Mon OB2 association. Even though an orbital solution has already been derived
for this system, few information are available about the individual stars. We
present, in this paper, the results of a long-term spectroscopic campaign. We
derive a new orbital solution and apply a disentangling method to recover the
mean spectrum of each star. To improve our knowledge concerning both
components, we determine their spectral classifications and their projected
rotational velocities. We also constrain the main stellar parameters of both
stars by using the CMFGEN atmosphere code and provide the wind properties for
the primary star through the study of IUE spectra. This investigation reveals
that HD 48099 is an O5.5 V((f))+O9 V binary with M_1 sin^3 i = 0.70 M_{\sun}
and M_2 sin^3 i = 0.39 M_{\sun}, implying a rather low orbital inclination.
This result, combined with both a large effective temperature and log g,
suggests that the primary star (v sini ~ 91 km s^-1) is actually a fast rotator
with a strongly clumped wind and a nitrogen abundance of about 8 times the
solar value.Comment: 12 pages, 7 figures, accepted by Ap
Effects of Hyperbolic Rotation in Minkowski Space on the Modeling of Plasma Accelerators in a Lorentz Boosted Frame
Laser driven plasma accelerators promise much shorter particle accelerators
but their development requires detailed simulations that challenge or exceed
current capabilities. We report the first direct simulations of stages up to 1
TeV from simulations using a Lorentz boosted calculation frame resulting in a
million times speedup, thanks to a frame boost as high as gamma=1300. Effects
of the hyperbolic rotation in Minkowski space resulting from the frame boost on
the laser propagation in the plasma is shown to be key in the mitigation of a
numerical instability that was limiting previous attempts
Qualitative understanding of the sign of t' asymmetry in the extended t-J Model and relevance for pairing properties
Numerical calculations illustrate the effect of the sign of the next
nearest-neighbor hopping term t' on the 2-hole properties of the t-t'-J model.
Working mainly on 2-leg ladders, in the -1.0 < t'/t < 1.0 regime, it is shown
that introducing t' in the t-J model is equivalent to effectively renormalizing
J, namely t' negative (positive) is equivalent to an effective t-J model with
smaller (bigger) J. This effect is present even at the level of a 2x2 plaquette
toy model, and was observed also in calculations on small square clusters.
Analyzing the transition probabilities of a hole-pair in the plaquette toy
model, it is argued that the coherent propagation of such hole-pair is enhanced
by a constructive interference between both t and t' for t'>0. This
interference is destructive for t'<0.Comment: 5 pages, 4 figures, to appear in PRB as a Rapid Communicatio
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