4,089 research outputs found
Impacto ambiental da cultura do arroz irrigado com uso de índice de qualidade de água (IQA).
O presente trabalho tem por objetivo avaliar o possível impacto da cultura do arroz irrigado sobre a qualidade das águas do Rio Camboriú (Camboriú/SC), através do estabelecimento de um índice de qualidade de água.bitstream/CNPMA/5829/1/comunicado_08.pd
Effective Widths and Effective Number of Phonons of Multiphonon Giant Resonances
We discuss the origin of the difference between the harmonic value of the
width of the multiphonon giant resonances and the smaller observed value.
Analytical expressions are derived for both the effective width and the average
cross-section. The contribution of the Brink-Axel mechanism in resolving the
discrepancy is pointed out.Comment: 9 pages, 4 figure
Computer simulation for the evaluation of recombination strategies in intrapopulation recurrent selection in Eucalyptus.
Intrapopulation recurrent selection (IRS) has proven to be a promising breeding method in eucalyptus, mainly through being easier to carry out when compared to reciprocal recurrent selection (RRS). However, the recombination strategies in IRS that have not yet been compared. Thus, the purpose of this study was to verify the efficiency of different recombination methods in IRS. To do so, computer simulation was used considering different heritabilities (0.1, 0.5, 1.0), different initial allelic frequencies (0.2, 0.8) and allelic interactions without dominance and with complete dominance. The initial population consisted of 1000 individuals, which were selected at random for the beginning of cycle zero. These individuals were interbred two by two. Three selection strategies were carried out and, consequently, three recombination methods: recombine the best individuals selected within the best progenies; the best individuals phenotypically selected regardless of their genealogy; or selection in the mean value of the best progenies selected. It was observed that recombination of the best individuals regardless of their genealogy and of the best individuals within the best progenies provided for gains superior to recombination having only the mean of the progenies as reference. The average degree of dominance and the heritability of the trait should be considered at the time of choosing the method of selection followed by recombination
On the energy-shell contributions of the three-particle~-~ three-hole excitations
The response functions for the extended second and third random phase
approximation are compared. A second order perturbation calculation shows that
the first-order amplitude for the direct excitation from the ground
state cancels with those that are engendered by the - coupling. As
a consequence nonvanishing effects to the response involve off
energy shell renormalization only. On shell processes are absent.Comment: 12 pages text (LaTex) and 1 figure included, to be published in Phys.
Rev.
Vector-meson magnetic dipole moment effects in radiative tau decays
We study the possibility that the magnetic dipole moment of light charged
vector mesons could be measured from their effects in \tau^- -->
V^-\nu_{\tau}\gamma decays. We conclude that the energy spectrum and angular
distribution of photons emitted at small angles with respect to vector mesons
is sensitive the effects of the magnetic dipole moment. Model-dependent
contributions and photon radiation off other electromagnetic multipoles are
small in this region. We also compute the effects of the magnetic dipole moment
on the integrated rates and photon energy spectrum of these lepton
decays.Comment: Latex, 12 pages, 4 figures, submitted to PR
Fermion Pairing Dynamics in the Relativistic Scalar Plasma
Using many-body techniques we obtain the time-dependent Gaussian
approximation for interacting fermion-scalar field models. This method is
applied to an uniform system of relativistic spin-1/2 fermion field coupled,
through a Yukawa term, to a scalar field in 3+1 dimensions, the so-called
quantum scalar plasma model. The renormalization for the resulting Gaussian
mean-field equations, both static and dynamical, are examined and initial
conditions discussed. We also investigate solutions for the gap equation and
show that the energy density has a single minimum.Comment: 21 pages, latex, 4 postscript figures, new sections, some literary
changes, notation corrections, accepted for publication in Phys. Rev
Electromagnetic couplings of elementary vector particles
On the basis of the three fundamental principles of (i) Poincar\'{e} symmetry
of space time, (ii) electromagnetic gauge symmetry, and (iii) unitarity, we
construct an universal Lagrangian for the electromagnetic interactions of
elementary vector particles, i.e., massive spin-1 particles transforming in the
/1/2,1/2) representation space of the Homogeneous Lorentz Group (HLG). We make
the point that the first two symmetries alone do not fix the electromagnetic
couplings uniquely but solely prescribe a general Lagrangian depending on two
free parameters, here denoted by \xi and g. The first one defines the
electric-dipole and the magnetic-quadrupole moments of the vector particle,
while the second determines its magnetic-dipole and electric-quadrupole
moments. In order to fix the parameters one needs an additional physical input
suited for the implementation of the third principle. As such, one chooses
Compton scattering off a vector target and requires the cross section to
respect the unitarity bounds in the high energy limit. In result, we obtain the
universal g=2, and \xi=0 values which completely characterize the
electromagnetic couplings of the considered elementary vector field at tree
level. The nature of this vector particle, Abelian versus non-Abelian, does not
affect this structure. Merely, a partition of the g=2 value into non-Abelian,
g_{na}, and Abelian, g_{a}=2-g_{na}, contributions occurs for non-Abelian
fields with the size of g_{na} being determined by the specific non-Abelian
group appearing in the theory of interest, be it the Standard Model or any
other theory.Comment: 10 pages, 2 figures, contributed to the XI Mexican Workshop on
Particles and Fields. Accepted in Phys. Rev.
Phases of quantum states in completely positive non-unitary evolution
We define an operational notion of phases in interferometry for a quantum
system undergoing a completely positive non-unitary evolution. This definition
is based on the concepts of quantum measurement theory. The suitable
generalization of the Pancharatnan connection allows us to determine the
dynamical and geometrical parts of the total phase between two states linked by
a completely positive map. These results reduce to the knonw expressions of
total, dynamical and geometrical phases for pure and mixed states evolving
unitarily.Comment: 2 figure
Alterações antropogênicas nos remanescentes de vegetação natural (RVN) de savana do estado de São Paulo no ano de 2009.
Deforestation in São Paulo State was mainly driven by sugarcane and coffee crops during the XVIII and XIX centuries which caused a significant fragmentation in native forests. More recently, between the 1970?s and 1980?s decades the native forest fragmentation process was intensified and also the savannah area was drastically reduced due to sugarcane expansion for ethanol production. Much native vegetation was deteriorated and fragmented into smaller disconnected portions during this period. This work was performed within the scope of a technical cooperative agreement between the Environmental Secretary of São Paulo State (SMA) and the National Institute for Space Research (INPE). It consisted in monitoring monthly the land cover changes of 7,000 polygons of remanescent native vegetation (RVN) in the São Paulo State. The environmental assessment of the vegetation cover status was performed based on mesoregions for better discussion of the geographical distribution of the deforested RVN's from May to December 2009. The results showed that Bauru and Ribeirão Preto mesoregions presented the highest land cover changes with 19.4 and 12.1 km², respectively
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