592 research outputs found
Localization of angiotensin II receptors in ovarian follicles and the identification of angiotensin II in rat ovaries.
A microscopic investigation of the transition form factor in the region of collective multipole excitations of stable and unstable nuclei
We have used a self-consistent Skyrme-Hartree-Fock plus Continuum-RPA model
to study the low-multipole response of stable and neutron/proton-rich Ni and Sn
isotopes. We focus on the momentum-transfer dependence of the strength
distribution, as it provides information on the structure of excited nuclear
states and in particular on the variations of the transition form factor (TFF)
with the energy. Our results show, among other things, that the TFF may show
significant energy dependence in the region of the isoscalar giant monopole
resonance and that the TFF corresponding to the threshold strength in the case
of neutron-rich nuclei is different compared to the one corresponding to the
respective giant resonance. Perspectives are given for more detailed future
investigations.Comment: 13 pages, incl. 9 figures; to appear in J.Phys.G,
http://www.iop.org/EJ/jphys
Enhancement of Threshold Cross Sections by In-Medium Final State Interactions
We address the problem of pion production in low energy -nucleus
collisions. For the production mechanism we assume a simple model consisting of
a coherent sum of single pion exchange and the excitation---followed by the
decay into two pions and a nucleon---of the resonance. The
production amplitude is modified by the final state interaction between the
pions calculated using the chirally improved J\"ulich meson exchange model
including the polarization of the nuclear medium by the pions. The model
reproduces well the experimentally observed cross
sections, especially the enhancement with increasing of the
mass distribution in the threshold region.Comment: 5 pages RevTeX, 3-eps figure
Renormalization of the P- and T-odd nuclear potentials by the strong interaction and enhancement of P-odd effective field
Approximate analytical formulas for the self-consistent renormalization of
P,T-odd and P-odd weak nuclear potentials by the residual nucleon-nucleon
strong interaction are derived. The contact spin-flip nucleon-nucleon
interaction reduces the constant of the P,T-odd potential 1.5 times for the
proton and 1.8 times for the neutron. Renormalization of the P-odd potential is
caused by the velocity dependent spin-flip component of the strong interaction.
In the standard variant of -exchange, the conventional strength
values lead to anomalous enhancement of the P-odd potential. Moreover, the
-meson exchange contribution seems to be large enough to generate an
instability (pole) in the nuclear response to a weak potential.Comment: 5 pages, Revtex3, no figure
Pion-nucleon scattering in a meson-exchange model
The pi-N interaction is studied within a meson-exchange model and in a
coupled-channels approach which includes the channels pi-N, eta-N, as well as
three effective pi-pi-N channels namely rho-N, pi-Delta, and sigma-N. Starting
out from an earlier model of the Julich group systematic improvements in the
dynamics and in some technical aspects are introduced. With the new model an
excellent quantitative reproduction of the pi-N phase shifts and inelasticity
parameters in the energy region up to 1.9 GeV and for total angular momenta J
leq 3/2 is achieved. Simultaneously, good agreement with data for the total and
differential pi-N -> eta-N transition cross sections is obtained. The
connection of the pi_N dynamics in the S_{11} partial wave with the reaction
pi-N -> eta-N is discussed.Comment: 32 pages, 9 figure
Meson model for f_0(980) production in peripheral pion-nucleon reactions
The Juelich model for pion-pion-scattering, based on an effective meson-meson
Lagrangian is applied to the analysis of the S-wave production amplitudes
derived from the BNL E852 experiment pi^- p -> pi^0 pi^0 n for a pion momentum
of 18.3 GeV. The unexpected strong dependence of the S-wave partial wave
amplitude on the momentum transfer between the proton and neutron in the
vicinity of the f_0(980) resonance is explained in our analysis as interference
effect between the correlated and uncorrelated pi^0 pi^0 pairs.Comment: 6 pages, 7 figures, formulas added, typos removed, new figure
One-body dissipation and chaotic dynamics in a classical simulation of a nuclear gas
In order to understand the origin of one-body dissipation in nuclei, we
analyze the behavior of a gas of classical particles moving in a
two-dimensional cavity with nuclear dimensions. This "nuclear" billiard has
multipole-deformed walls which undergo periodic shape oscillations. We
demonstrate that a single particle Hamiltonian containing coupling terms
between the particles' motion and the collective coordinate induces a chaotic
dynamics for any multipolarity, independently on the geometry of the billiard.
If the coupling terms are switched off the "wall formula" predictions are
recovered. We discuss the dissipative behavior of the wall motion and its
relation with the order-to-chaos transition in the dynamics of the microscopic
degrees of freedom.Comment: 16 pages, 12 postscript figures included, revtex, new version
completely revised accepted by Physical Review C and scheduled to appear in
the issue of november 199
Microscopics of meson degrees of freedom in nucleons and mesons in nuclei - what can be seen in the process of quasielastic knockout of mesons by high-energy electrons
Developed earlier concept of quasielastic knock out of pions from nucleons by
high-energy electrons is propounded as a tool for checking microscopical model
( - fluctuation) for decay of N to different channels and
Preparata model of nucleus structure.Comment: 6 pages, 5 figures, Talk given at 16 Baldin Symposium in June 200
Short-range correlations in low-lying nuclear excited states
The electromagnetic transitions to various low-lying excited states of 16O,
48Ca and 208Pb are calculated within a model which considers the short-range
correlations. In general the effects of the correlations are small and do not
explain the required quenching to describe the data.Comment: 6 pages, 2 postscript figures, 1 tabl
The longitudinal and transverse responses in the inclusive electron scattering: a functional approach
The splitting between the charge-longitudinal and spin-transverse responses
is explained in a model whose inputs are the effective interactions in the
particle-hole channels in the frame of the first order boson loop expansion. It
is shown that the interplay between -meson exchange and box diagrams
(two-meson exchange with simultaneous excitation of one or two nucleons to
's) mainly rules the longitudinal response, while in the transverse one
the direct excitations almost cancel the one-loop correction and the
response is mainly governed by the -meson rescattering inside the
nucleus. It is also shown that a small variation in the nuclear densities may
explain the observed discrepancies between different nuclei.Comment: LaTex2e file with 53 .ps figures; submitted to Nucl. Phys
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