11,738 research outputs found
Método exploratório de indicadores de adoção de variedades melhoradas.
Neste boletim de pesquisa, é proposto um método exploratório para calcular os indicadores de adoção de variedades melhoradas, especialmente recomendado em caso de ausência de séries históricas acerca do processo de adoção. A quase ausência desses dados constitui o principal obstáculo à realização de estudos de adoção de variedades melhoradas na Embrapa. Portanto, o método proposto contribui ao tornar possível estudo dessa natureza a partir da coleta, em campo, de um conjunto mínimo de dados acerca do processo de adoção de variedades melhoradas. O método é composto por 12 indicadores de adoção, agrupados em três categorias principais: alcance, velocidade e eficiência. Embora o método proposto possa ser utilizado para lavouras temporárias e permanentes, a título de exemplo, e unicamente com este propósito, são calculados os indicadores de adoção de duas variedades de mandioca lançadas pela Embrapa: BRS Formosa e BRS Kiriris. Os indicadores foram elaborados por ocasião da submissão do projeto ?Impacto da pesquisa participativa do melhoramento genético da mandioca no bioma caatinga?, ao macroprograma 4 da Embrapa, sob a liderança da Embrapa Mandioca e Fruticultura.bitstream/item/100889/1/boletim-59-Finalizado-novamente-alterado.pd
Replica-symmetric solutions of a dilute Ising ferromagnet in a random field
We use the replica method in order to obtain an expression for the
variational free energy of an Ising ferromagnet on a Viana-Bray lattice in the
presence of random external fields. Introducing a global order parameter, in
the replica-symmetric context, the problem is reduced to the analysis of the
solutions of a nonlinear integral equation. At zero temperature, and under some
restrictions on the form of the random fields, we are able to perform a
detailed analysis of stability of the replica-symmetric solutions. In contrast
to the behaviour of the Sherrington-Kirkpatrick model for a spin glass in a
uniform field, the paramagnetic solution is fully stable in a sufficiently
large random field
A method for evaluating models that use galaxy rotation curves to derive the density profiles
There are some approaches, either based on General Relativity (GR) or
modified gravity, that use galaxy rotation curves to derive the matter density
of the corresponding galaxy, and this procedure would either indicate a partial
or a complete elimination of dark matter in galaxies. Here we review these
approaches, clarify the difficulties on this inverted procedure, present a
method for evaluating them, and use it to test two specific approaches that are
based on GR: the Cooperstock-Tieu (CT) and the Balasin-Grumiller (BG)
approaches. Using this new method, we find that neither of the tested
approaches can satisfactorily fit the observational data without dark matter.
The CT approach results can be significantly improved if some dark matter is
considered, while for the BG approach no usual dark matter halo can improve its
results.Comment: 11 pages, 2 figures, 4 tables. v2: diverse text improvements, no
changes in the conclusions. Version accepted in MNRA
Quantum Baker Maps for Spiraling Chaotic Motion
We define a coupling of two baker maps through a pi/2 rotation both in
position and in momentum. The classical trajectories thus exhibit spiraling, or
loxodromic motion, which is only possible for conservative maps of at least two
degrees of freedom. This loxodromic baker map is still hyperbolic, that is,
fully chaotic. Quantization of this map follows on similar lines to other
generalized baker maps. It is found that the eigenvalue spectrum for quantum
loxodromic baker map is far removed from those of the canonical random matrix
ensembles. An investigation of the symmetries of the loxodromic baker map
reveals the cause of this deviation from the Bohigas-Giannoni-Schmit
conjecture
Quantum revival patterns from classical phase-space trajectories
A general semiclassical method in phase space based on the final value
representation of the Wigner function is considered that bypasses caustics and
the need to root-search for classical trajectories. We demonstrate its
potential by applying the method to the Kerr Hamiltonian, for which the exact
quantum evolution is punctuated by a sequence of intricate revival patterns.
The structure of such revival patterns, lying far beyond the Ehrenfest time, is
semiclassically reproduced and revealed as a consequence of constructive and
destructive interferences of classical trajectories.Comment: 7 pages, 6 figure
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