9,375 research outputs found
On the splitting of nucleon effective masses at high isospin density: reaction observables
We review the present status of the nucleon effective mass splitting
in asymmetric matter, with controversial predictions within both
non-relativistic relativistic approaches to the effective in medium
interactions. Based on microscopic transport simulations we suggest some rather
sensitive observables in collisions of asymmetric (unstable) ions at
intermediate () energies: i) Energy systematics of Lane Potentials; ii)
Isospin content of fast emitted nucleons; iii) Differential Collective Flows.
Similar measurements for light isobars (like ) could be also
important.Comment: 13 pages, 10 figures; NSCL/RIA Workshop on "Reaction Mechanisms for
Rare Isotope Beams", March 2005, AIP Proc. Latex Styl
Algebraic structure of multi-parameter quantum groups
Multi-parameter versions U_p(g) and C_p[G] of the standard quantum groups
U_q(g) and C_q[G] are considered where G is a semi-simple connected complex
algebraic group and g is the Lie algebra of G. The primitive spectrum of C_p[G]
is calculated, generalizing a result of Joseph for the standard quantum groups.
This classification is compared with the classification of symplectic leaves
for the associated Poisson structure on G.Comment: AMS Latex, 37 pages, June 1994; to appear in Advances in Mat
On Fabry P\'erot Etalon based Instruments. I. The Isotropic Case
Here we assess the spectral and imaging properties of Fabry P\'erot etalons
when located in solar magnetographs. We discuss the chosen configuration
(collimated or telecentric) for both ideal and real cases. For the real cases,
we focus on the effects caused by the polychromatic illumination of the filter
by the irregularities in the optical thickness of the etalon and by deviations
from the ideal illumination in both setups. We first review the general
properties of Fabry P\'erots and we then address the different sources of
degradation of the spectral transmission profile. We review and extend the
general treatment of defects followed by different authors. We discuss the
differences between the point spread functions (PSFs) of the collimated and
telecentric configurations for both monochromatic and (real)
quasi-monochromatic illumination of the etalon. The PSF corresponding to
collimated mounts is shown to have a better performance, although it varies
from point to point due to an apodization of the image inherent to this
configuration. This is in contrast to the (perfect) telecentric case, where the
PSF remains constant but produces artificial velocities and magnetic field
signals because of its strong spectral dependence. We find that the unavoidable
presence of imperfections in the telecentrism produces a decrease of flux of
photons and a shift, a broadening and a loss of symmetrization of both the
spectral and PSF profiles over the field of view, thus compromising their
advantages over the collimated configuration. We evaluate these effects for
different apertures of the incident beam.Comment: 20 pages 22 figures 2 Appendice
Fast nucleon emission as a probe of the isospin momentum dependence
In this article we investigate the structure of the non-local part of the
symmetry term, that leads to a splitting of the effective masses of protons and
neutrons in asymmetric matter. Based on microscopic transport simulations we
suggest some rather sensitive observables in collisions of neutron-rich
(unstable) ions at intermediate () energies. In particular we focus the
attention on pre-equilibrium nucleon emissions. We discuss interesting
correlations between the N/Z content of the fast emitted particles and their
rapidity or transverse momentum, that show a nice dependence on the
prescription used for the effective mass splitting.Comment: 5 pages, 6 figures, revtex
Isospin emission and flows at high baryon density: a test of the symmetry potential
High energy Heavy Ion Collisions (HIC) are studied in order to access nuclear
matter properties at high density. Particular attention is paid to the
selection of observables sensitive to the poorly known symmetry energy at high
baryon density, of large fundamental interest, even for the astrophysics
implications. Using fully consistent transport simulations built on effective
theories we test isospin observables ranging from nucleon/cluster emissions to
collective flows (in particular the elliptic, squeeze out, part). The effects
of the competition between stiffness and momentum dependence of the Symmetry
Potential on the reaction dynamics are thoroughly analyzed. In this way we try
to shed light on the controversial neutron/proton effective mass splitting at
high baryon and isospin densities. New, more exclusive, experiments are
suggested.Comment: 10 pages, 16 figures, new figure added, accepted for publication in
Phys.Rev.
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