180 research outputs found
Estudo da estabilidade da linamarase de manihot esculenta crantz sob armazenamento.
A linamarase Ă© uma β-glicosidase que pode ser obtida, dentre outras fontes, da mandioca. Ela Ă© responsável pela hidrĂłlise dos glicosĂdeos cianogĂŞnicos linamarina e lotaustralina, que se supõe estĂŁo envolvidos em processos de defesa da planta
Correlations and charge distributions of medium heavy nuclei
The effects of long- and short-range correlations on the charge distributions
of some medium and heavy nuclei are investigated. The long-range correlations
are treated within the Random Phase Approximation framework and the short-range
correlations with a model inspired to the Correlation Basis Function theory.
The two type of correlations produce effects of the same order of magnitude. A
comparison with the empirical charge distribution difference between 206Pb and
205Tl shows the need of including both correlations to obtain a good
description of the data.Comment: 20 pages, Latex, accepted for publication in Jour. Phys.
Neutron Star Structure and the Neutron Radius of 208Pb
We study relationships between the neutron-rich skin of a heavy nucleus and
the properties of neutron-star crusts. Relativistic effective field theories
with a thicker neutron skin in Pb have a larger electron fraction and a
lower liquid-to-solid transition density for neutron-rich matter. These
properties are determined by the density dependence of the symmetry energy
which we vary by adding nonlinear couplings between isoscalar and isovector
mesons. An accurate measurement of the neutron radius in Pb---via
parity violating electron scattering---may have important implications for the
structure of neutron stars.Comment: 5 pages 3 figures, added additional evidence of model independence,
Phys. Rev. Letters in pres
First electron beam polarization measurements with a Compton polarimeter at Jefferson Laboratory
A Compton polarimeter has been installed in Hall A at Jefferson Laboratory.
This letter reports on the first electron beam polarization measurements
performed during the HAPPEX experiment at an electron energy of 3.3 GeV and an
average current of 40 A. The heart of this device is a Fabry-Perot cavity
which increased the luminosity for Compton scattering in the interaction region
so much that a 1.4% statistical accuracy could be obtained within one hour,
with a 3.3% total error
Effects of Short Range Correlations on Ca Isotopes
The effect of Short Range Correlations (SRC) on Ca isotopes is studied using
a simple phenomenological model. Theoretical expressions for the charge
(proton) form factors, densities and moments of Ca nuclei are derived. The role
of SRC in reproducing the empirical data for the charge density differences is
examined. Their influence on the depletion of the nuclear Fermi surface is
studied and the fractional occupation probabilities of the shell model orbits
of Ca nuclei are calculated. The variation of SRC as function of the mass
number is also discussed.Comment: 11 pages (RevTex), 6 Postscript figures available upon request at
[email protected] Physical Review C in prin
Description of nuclear systems within the relativistic Hartree-Fock method with zero range self-interactions of the scalar field
An exact method is suggested to treat the nonlinear self-interactions (NLSI)
in the relativistic Hartree-Fock (RHF) approach for nuclear systems. We
consider here the NLSI constructed from the relativistic scalar nucleon
densities and including products of six and eight fermion fields. This type of
NLSI corresponds to the zero range limit of the standard cubic and quartic
self-interactions of the scalar field. The method to treat the NLSI uses the
Fierz transformation, which enables one to express the exchange (Fock)
components in terms of the direct (Hartree) ones. The method is applied to
nuclear matter and finite nuclei. It is shown that, in the RHF formalism, the
NLSI, which are explicitly isovector-independent, generate scalar, vector and
tensor nucleon self-energies strongly density-dependent. This strong isovector
structure of the self-energies is due to the exchange terms of the RHF method.
Calculations are carried out with a parametrization containing five free
parameters. The model allows a description of both types of systems compatible
with experimental data.Comment: 23 pages, 14 figures (v2: major quantitative changes
Parity violating elastic electron scattering and neutron density distributions in the Relativistic Hartree-Bogoliubov model
Parity violating elastic electron scattering on neutron-rich nuclei is
described in the framework of relativistic mean-field theory. Self-consistent
ground state density distributions of Ne, Na, Ni and Sn isotopes are calculated
with the relativistic Hartree- Bogoliubov model, and the resulting neutron
radii are compared with available experimental data. For the elastic scattering
of 850 MeV electrons on these nuclei, the parity-violating asymmetry parameters
are calculated using a relativistic optical model with inclusion of Coulomb
distortion effects. The asymmetry parameters for chains of isotopes are
compared, and their relation to the Fourier transforms of neutron densities is
studied. It is shown that parity-violating asymmetries are sensitive not only
to the formation of the neutron skin, but also to the shell effects of the
neutron density distribution.Comment: RevTeX 17 pages, 18 eps figs, submitted to Phys. Rev.
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