12,340 research outputs found
Two-particle irreducible effective action approach to nonlinear current conserving approximations in driven systems
Using closed-time path two-particle irreducible coarse-grained effective
action (CTP 2PI CGEA) techniques, we study the response of an open interacting
electronic system to time-dependent external electromagnetic fields. We show
that the CTP 2PI CGEA is invariant under a simultaneous gauge transformation of
the external field and the full Schwinger-Keldysh propagator, and that this
property holds even when the loop expansion of the CTP 2PI CGEA is truncated at
arbitrary order. The effective action approach provides a systematic way of
calculating the propagator and response functions of the system, via the
Schwinger-Dyson equation and the Bethe-Salpeter equations, respectively. We
show that, due to the invariance of the CTP 2PI CGEA under external gauge
transformations, the response functions calculated from it satisfy the
Ward-Takahashi hierarchy, thus warranting the conservation of the electronic
current beyond the expectation value level. We also clarify the connection
between nonlinear response theory and the WT hierarchy, and discuss an example
of an ad hoc approximation that violate it. These findings may be useful in the
study of current fluctuations in correlated electronic pumping devices.Comment: 30 pages. Accepted for publication in JPC
production in the reaction
We discuss the mechanisms that lead to production in the
reaction. The problem has gained renewed interest
after different works converge to the conclusion that there are two resonances
around the region of 1400 MeV, rather than one, and that they couple
differently to the and channels. We look at the dynamics
of that reaction and find two mechanisms which eventually filter each one of
the resonances, leading to very different shapes of the invariant
mass distributions. The combination of the two mechanisms leads to a shape of
this distribution compatible with the experimental measurements.Comment: RevTeX4, 10 pages, 8 figures, 2 tables, Version to appear in Phys.
Rev.
Neutron and proton spectra from the decay of hypernuclei
We have determined the spectra of neutrons and protons following the decay of
hypernuclei through the one- and two-nucleon induced mechanisms. The
momentum distributions of the primary nucleons are calculated and a Monte Carlo
simulation is used to account for final state interactions. From the spectra we
calculate the number of neutrons () and protons () per
decay and show how the measurement of these quantities, particularly , can
lead to a determination of , the ratio of neutron to
proton induced decay. We also show that the consideration of the
two-nucleon induced channel has a repercussion in the results, widening the
band of allowed values of with respect to what is
obtained neglecting this channel.Comment: 30 pages, 12 Postscript figures, uuencoded file, ReVTeX, epsf.st
Lixiviação de íons potássio, cálcio e magnésio para determinação do vigor em sementes de milho doce.
O teste de lixiviação de íons de potássio, cálcio e magnésio é baseado na integridade das membranas celulares das sementes, sendo considerado um procedimento rápido para a avaliação do vigor em sementes de várias espécies. Porém, para sementes de milho doce não se têm informações necessárias para a validação deste procedimento. Com isso, o trabalho teve como objetivo obter informações que permitam o aperfeiçoamento dos testes de lixiviação de potássio, cálcio e magnésio para a avaliação do vigor em sementes de milho doce. Foram utilizados 14 lotes de sementes de milho doce de duas cultivares, BR-401 e BR-402. O delineamento utilizado foi inteiramente casualizado com três repetições. A qualidade fisiológica das sementes foi avaliada por meio dos testes de germinação, condutividade elétrica, emergência a campo, lixiviação de potássio, de cálcio e de magnésio. Os testes de lixiviação de potássio e magnésio foram eficientes na avaliação do vigor em sementes de milho doce. A condutividade elétrica apresentou correlação negativa com a emergência de plântulas e positiva com a lixiviação de íons de potássio e magnésio
The Zeeman effect in the G band
We investigate the possibility of measuring magnetic field strength in G-band
bright points through the analysis of Zeeman polarization in molecular CH
lines. To this end we solve the equations of polarized radiative transfer in
the G band through a standard plane-parallel model of the solar atmosphere with
an imposed magnetic field, and through a more realistic snapshot from a
simulation of solar magneto-convection. This region of the spectrum is crowded
with many atomic and molecular lines. Nevertheless, we find several instances
of isolated groups of CH lines that are predicted to produce a measurable
Stokes V signal in the presence of magnetic fields. In part this is possible
because the effective Land\'{e} factors of lines in the stronger main branch of
the CH A--X transition tend to zero rather quickly for
increasing total angular momentum , resulting in a Stokes spectrum of
the G band that is less crowded than the corresponding Stokes spectrum. We
indicate that, by contrast, the effective Land\'{e} factors of the and
satellite sub-branches of this transition tend to for increasing .
However, these lines are in general considerably weaker, and do not contribute
significantly to the polarization signal. In one wavelength location near 430.4
nm the overlap of several magnetically sensitive and non-sensitive CH lines is
predicted to result in a single-lobed Stokes profile, raising the
possibility of high spatial-resolution narrow-band polarimetric imaging. In the
magneto-convection snapshot we find circular polarization signals of the order
of 1% prompting us to conclude that measuring magnetic field strength in
small-scale elements through the Zeeman effect in CH lines is a realistic
prospect.Comment: 22 pages, 6 figures. To be published in the Astrophysical Journa
Seleção de primers ISSR para genotipagem de murici.
O muricizeiro, espécie frutífera da família Malpighiaceae, encontra-se disperso em todo o território brasileiro. A Embrapa possui plantas matrizes que precisam ser caracterizadas à nível de DNA. Nesse sentido, os materiais vegetais foram coletados da coleção da Embrapa Amazônia Oriental e conservadas no banco de DNA dessa intuição. As reações de PCR-ISSR foram realizadas testando 100 primer disponíveis em cinco clones de muricizeiro, com objetivo de selecionar os melhores fragmentos polimórficos para os materiais de murici, totalizando no mínimo 100 bandas polimórfica
Variabilidade espacial da população do nematoide de cisto e sua relação com a acidez do solo e a produtividade da soja de 2ª safra.
Densidade populacional do nematoide das lesões radiculares em soja e sua relação com a calagem.
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