574 research outputs found
On the eikonal approach to nuclear diffraction dissociation
The study of nuclear breakup of halo and weakly bound particles has been one
of the key ingredients in the understanding of exotic nuclei during the last
thirty years. One of the most used methods to analyse data, in particular
absolute breakup cross sections, has been the eikonal approximation. Here we
revise critically the formalisms used for calculating the diffraction
dissociation part of nuclear breakup and show that there is a formula that can
be applied to breakup on any target, while a most commonly used formula must be
restricted to light targets as it contains also the effect of Coulomb breakup
calculated to first order in the sudden approximation which is well known for
not being accurate.Comment: 5 pages, 1 figur
Proton vs. neutron halo breakup
In this paper we show how effective parameters such as effective binding
energies can be defined for a proton in the combined nuclear-Coulomb potential,
including also the target potential, in the case in which the proton is bound
in a nucleus which is partner of a nuclear reaction. Using such effective
parameters the proton behaves similarly to a neutron. In this way some
unexpected results obtained from dynamical calculations for reactions initiated
by very weakly bound proton halo nuclei can be interpreted. Namely the fact
that stripping dominates the nuclear breakup cross section which in turn
dominates over the Coulomb breakup even when the target is heavy at medium to
high incident energies. Our interpretation helps also clarifying why the
existence and characteristics of a proton halo extracted from different types
of data have sometimes appeared contradictory.Comment: 7 Latex pages, 3 table, 3 ps figures, to appear in Phys. Rev.
Influence of Tunneling on Electron Screening in Low Energy Nuclear Reactions
Using a semiclassical mean field theory, we show that the screening potential exhibits a characteristic radial variation in the tunneling region in sharp contrast to the assumption of the constant shift in all previous works. Also, we show that the explicit treatment of the tunneling region gives a larger screening energy than that in the conventional approach, which studies the time evolution only in the classical region and estimates the screening energy from the screening potential at the external classical turning point. This modification becomes important if the electronic state is not a single adiabatic state at the external turning point. Furthermore, as an alternative solution of the screening problem, we give the estimation for the effect of extra electrons which are caught into the ground state of the projectile by using constraint molecular dynamics
Influence of tunneling on electron screening in low energy nuclear reactions in laboratories
Using a semiclassical mean field theory, we show that the screening potential
exhibits a characteristic radial variation in the tunneling region in sharp
contrast to the assumption of the constant shift in all previous works. Also,
we show that the explicit treatment of the tunneling region gives a larger
screening energy than that in the conventional approach, which studies the time
evolution only in the classical region and estimates the screening energy from
the screening potential at the external classical turning point. This
modification becomes important if the electronic state is not a single
adiabatic state at the external turning point either by pre-tunneling
transitions of the electronic state or by the symmetry of the system even if
there is no essential change with the electronic state in the tunneling region.Comment: 3 figure
Effects of Field Peas in Beef Finishing Diets
Feeding field peas was compared to using corn in beef finishing diets. Diets containing field peas at 0%, 20%, 40%, and 59% replacement of corn in ration DM were fed to 129 steers. Dry matter intake increased from the 0% to 40% diets, but decreased when 59% peas replaced corn compared to 40%. No significant differences in ADG and G:F were observed. Field peas can replace 59% of the corn DM in beef finishing diet with no significant differences in animal gain or feed efficiency
Geophysical evidence for the evolution of the California Inner Continental Borderland as a metamorphic core complex
Author Posting. © American Geophysical Union, 2000. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 105 (2000): 5835-5857, doi:10.1029/1999JB900318.We use new seismic and gravity data collected during the 1994 Los Angeles
Region Seismic Experiment (LARSE) to discuss the origin of the California Inner
Continental Borderland (ICB) as an extended terrain possibly in a metamorphic core
complex mode. The data provide detailed crustal structure of the Borderland and its
transition to mainland southern California. Using tomographic inversion as well as
traditional forward ray tracing to model the wide-angle seismic data, we find little or no
sediments, low (#6.6 km/s) P wave velocity extending down to the crust-mantle boundary,
and a thin crust (19 to 23 km thick). Coincident multichannel seismic reflection data show
a reflective lower crust under Catalina Ridge. Contrary to other parts of coastal
California, we do not find evidence for an underplated fossil oceanic layer at the base of
the crust. Coincident gravity data suggest an abrupt increase in crustal thickness under the
shelf edge, which represents the transition to the western Transverse Ranges. On the shelf
the Palos Verdes Fault merges downward into a landward dipping surface which separates
“basement” from low-velocity sediments, but interpretation of this surface as a detachment
fault is inconclusive. The seismic velocity structure is interpreted to represent Catalina
Schist rocks extending from top to bottom of the crust. This interpretation is compatible
with a model for the origin of the ICB as an autochthonous formerly hot highly extended
region that was filled with the exhumed metamorphic rocks. The basin and ridge
topography and the protracted volcanism probably represent continued extension as a
wide rift until ;13 m.y. ago. Subduction of the young and hot Monterey and Arguello
microplates under the Continental Borderland, followed by rotation and translation of the
western Transverse Ranges, may have provided the necessary thermomechanical
conditions for this extension and crustal inflow.The LARSE experiment
was funded by NSF EAR-9416774, the U.S. Geological Survey’s Earthquake
Hazards and Coastal and Marine Programs, and by the Southern
California Earthquake Center (SCEC)
Critical Boundary Conditions for the Effective String
Gauge systems in the confining phase induce constraints at the boundaries of
the effective string, which rule out the ordinary bosonic string even with
short distance modifications. Allowing topological excitations, corresponding
to winding around the colour flux tube, produces at the quantum level a
universal free fermion string with a boundary phase nu=1/4. This coincides with
a model proposed some time ago in order to fit Monte Carlo data of 3D and 4D
Lattice gauge systems better. A universal value of the thickness of the colour
flux tube is predicted.Comment: 9 pages + 1 figur
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