Dep. de Fisica

Itabaiana, Brazil

Dep. de Fisica

Itabaiana, Brazil
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Salme G.,National Institute of Nuclear Physics, Italy | Frederico T.,Dep. de Fisica | Pace E.,University of Rome Tor Vergata
Few-Body Systems | Year: 2015

Information on the non perturbative content of the proton state, in particular on the non valence contribution, could be extracted from the analysis of the ratio between the electric and magnetic form factors of the proton, given the highly accurate data from JLAB, obtained in the past and available in the very close future. This possibility is illustrated within our approach based on an Ansatz for the Bethe-Salpeter amplitude describing the quark-nucleon vertex and a Vector Meson Dominance model for the quark-photon one. After presenting a short review of our approach, able to predict the presence of a zero in the above ratio with only four free parameters fixed by three spacelike nucleon form factors, we give preliminary results for the nucleon timelike polarizations, that are quite sensitive to the Vector meson spectra. © 2015, Springer-Verlag Wien.


Salme G.,National Institute of Nuclear Physics, Italy | Frederico T.,Dep. de Fisica | Viviani M.,National Institute of Nuclear Physics, Italy
Few-Body Systems | Year: 2014

The Bethe-Salpeter equation for a two-scalar, S-wave bound system, interacting through a massive scalar, is investigated within the ladder approximation. By assuming a Nakanishi integral representation of the Bethe-Salpeter amplitude, one can deduce new integral equations that can be solved and quantitatively studied, overcoming the analytic difficulties of the Minkowski space. Finally, it is shown that the Light-front distributions of the valence state, directly obtained from the Bethe-Salpeter amplitude, open an effective window for studying the two-body dynamics. © 2014 Springer-Verlag Wien.


Mendona E.C.,Dep. de Fisica | Jesus C.B.R.,Dep. de Fisica | Folly W.S.D.,Dep. de Fisica | Meneses C.T.,Dep. de Fisica | And 2 more authors.
Journal of Applied Physics | Year: 2012

Structural and magnetic measurements on ZnFe 2O 4 nanoparticles obtained through co-precipitation chemical method are reported. The Rietveld analysis of X-ray patterns reveal that (i) our samples are single phase, and (ii) the average particle size increases with synthesis temperature. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements show that the average blocking temperature increases for increasing mean particle size. Besides, one can observe via magnetization measurements that our particle size distribution also increases as a function of synthesis temperature. Finally, we have observed that the coercive field does not decay with the square root of temperature following the Néel relaxation and the Bean-Livingston approaches. In order to fit our experimental data, we have used a generalized model that proposes a temperature dependence of blocking temperature due to the coexistence of blocked and unblocked particles. This proposed generalized model shows good agreement with our experimental results. © 2012 American Institute of Physics.


Mendonca E.C.,Dep. de Fisica | Jesus C.B.R.,Dep. de Fisica | Folly W.S.D.,Dep. de Fisica | Meneses C.T.,Dep. de Fisica | Duque J.G.S.,Dep. de Fisica
Journal of Superconductivity and Novel Magnetism | Year: 2013

We report structural and magnetic measurements on ZnFe2O 4 nanoparticles obtained through coprecipitation chemical method. The Rietveld analysis of X-ray patterns reveals that (i) our samples are single phase, (ii) the average particle size increases with synthesis temperature, and (iii) the cationic disorder increases with decreasing of the mean particle size. The Zero-Field-Cooled (ZFC) and Field-Cooled (FC) magnetization measurements show that the blocking temperature increases with increasing of the particle size and, to the sample grown at T=850 C, it is possible to observe both Néel temperature to larger particles and blocking effects to smaller particles. Finally, we have observed that the coercive field does not decay with the square root of temperature following the Néel relaxation and Bean-Livingston approaches. © 2012 Springer Science+Business Media, LLC.

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