54 research outputs found
Electromagnetic Dissociation of Nuclei in Heavy-Ion Collisions
Large discrepancies have been observed between measured Electromagnetic
Dissociation(ED) cross sections and the predictions of the semiclassical
Weiz\"acker-Williams-Fermi(WWF) method. In this paper, the validity of the
semiclassical approximation is examined. The total cross section for
electromagnetic excitation of a nuclear target by a spinless projectile is
calculated in first Born approximation, neglecting recoil. The final result is
expressed in terms of correlation functions and convoluted densities in
configuration space. The result agrees with the WWF approximation to leading
order(unretarded electric dipole approximation), but the method allows an
analytic evaluation of the cutoff, which is determined by the details of the
electric dipole transition charge density. Using the Goldhaber-Teller model of
that density, and uniform charge densities for both projectile and target, the
cutoff is determined for the total cross section in the nonrelativistic limit,
and found to be smaller than values currently used for ED calculations. In
addition, cross sections are calculated using a phenomenological momentum space
cutoff designed to model final state interactions. For moderate projectile
energies, the calculated ED cross section is found to be smaller than the
semiclassical result, in qualitative agreement with experiment.Comment: 28 page
Rotating inclined cylinder and the effect of the tilt angle on vortices
We study numerically some possible vortex configurations in a rotating
cylinder that is tilted with respect to the rotation axis and where different
numbers of vortices can be present at given rotation velocity. In a long
cylinder at small tilt angles the vortices tend to align along the cylinder
axis and not along the rotation axis. We also show that the axial flow along
the cylinder axis, caused by the tilt, will result in the Ostermeier-Glaberson
instability above some critical tilt angle. When the vortices become unstable
the final state often appears to be a dynamical steady state, which may contain
turbulent regions where new vortices are constantly created. These new vortices
push other vortices in regions with laminar flow towards the top and bottom
ends of the cylinder where they finally annihilate. Experimentally the inclined
cylinder could be a convenient environment to create long lasting turbulence
with a polarization which can be adjusted with the tilt angle.Comment: 10 pages, 10 figure
Effects of Microneedle Length, Density, Insertion Time and Multiple Applications on Human Skin Barrier Function: Assessments by Transepidermal Water Loss
Decomposition of hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane on, and diffusion of Cu into single crystal and polycrystalline titanium nitride
Search for light penetrating bosons with the use of a rotatable detector arrangement at a nuclear reactor
The effects of radiation damage and impurities on void dynamics in silicon
Transmission electron microscopy (TEM) has been used to study the effects of implanted oxygen or carbon on the dynamics of cavity growth in silicon. The cavities are produced by implantation with helium ions followed by annealing to convert small He-filled bubbles into large empty voids. We have also investigated the effects of self-ion damage on cavity growth. Both impurities and self-ion damage can significantly inhibit void growth. In addition, hot stage TEM has been used to elucidate the processes responsible for cavity growth in an attempt to understand the way in which both impurities and radiation damage are able to modify these processes. Cavity growth is seen to be due to Ostwald ripening and coalescence in the early stages with some sporadic, rapid motion of large bubbles leading to coalescence at higher temperatures. Our research indicates that void dynamics in silicon are quite different from those in metallic systems
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