12,807 research outputs found
Managing migration: the Brazilian case
The objective of this paper is to present the Brazilian migration experience and its relationship with migration management. The article is divided into three parts. First, it reviews some basic facts regarding Brazilian immigration and emigration processes. Second, it focuses on some policy and legal issues related to migration. Finally, it addresses five issues regarding migration management in Brazil.international migration, immigration, emigration, migration management, migration policies, migration laws, Brazil
A procedure for testing the quality of LANDSAT atmospheric correction algorithms
There are two basic methods for testing the quality of an algorithm to minimize atmospheric effects on LANDSAT imagery: (1) test the results a posteriori, using ground truth or control points; (2) use a method based on image data plus estimation of additional ground and/or atmospheric parameters. A procedure based on the second method is described. In order to select the parameters, initially the image contrast is examined for a series of parameter combinations. The contrast improves for better corrections. In addition the correlation coefficient between two subimages, taken at different times, of the same scene is used for parameter's selection. The regions to be correlated should not have changed considerably in time. A few examples using this proposed procedure are presented
On the Consistency of a Fermion-Torsion Effective Theory
We discuss the possibility to construct an effective quantum field theory for
an axial vector coupled to a Dirac spinor field. A massive axial vector
describes antisymmetric torsion. The consistency conditions include unitarity
and renormalizability in the low-energy region. The investigation of the Ward
identities and the one- and two-loop divergences indicate serious problems
arising in the theory. The final conclusion is that torsion may exist as a
string excitation, but there are very severe restrictions for the existence of
a propagating torsion field, subject to the quantization procedure, at low
energies.Comment: LaTeX, 26 pages, 4 figure
Canonical transformation for stiff matter models in quantum cosmology
In the present work we consider Friedmann-Robertson-Walker models in the
presence of a stiff matter perfect fluid and a cosmological constant. We write
the superhamiltonian of these models using the Schutz's variational formalism.
We notice that the resulting superhamiltonians have terms that will lead to
factor ordering ambiguities when they are written as operators. In order to
remove these ambiguities, we introduce appropriate coordinate transformations
and prove that these transformations are canonical using the symplectic method.Comment: Revtex4 Class, 3 pages, No Figure
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