145 research outputs found
A design and a code invariant under the simple group Co3
Mathematics;mathematics
On affine designs and Hadamard designs with line spreads
Rahilly [10] described a construction that relates any Hadamard design H on 4 m −1 points with a line spread to an affine design having the same parameters as the classical design of points and hyperplanes in AG(m, 4). Here it is proved that the affine design is the classical design of points and hyperplanes in AG(m, 4) if, and only if, H is the classical design of points and hyperplanes in P G(2m−1, 2) and the line spread is of a special type. Computational results about line spreads in P G(5, 2) are given. One of the affine designs obtained has the same 2-rank as the design of points and planes in AG(3, 4), and provides a counter-example to a conjecture o
Investigation of Pygmy Dipole Resonances in the Tin Region
The evolution of the low-energy electromagnetic dipole response with the
neutron excess is investigated along the Sn isotopic chain within an approach
incorporating Hartree-Fock-Bogoljubov (HFB) and multi-phonon
Quasiparticle-Phonon-Model (QPM) theory. General aspects of the relationship of
nuclear skins and dipole sum rules are discussed. Neutron and proton transition
densities serve to identify the Pygmy Dipole Resonance (PDR) as a generic mode
of excitation. The PDR is distinct from the GDR by its own characteristic
pattern given by a mixture of isoscalar and isovector components. Results for
the Sn-Sn isotopes and the several N=82 isotones are presented.
In the heavy Sn-isotopes the PDR excitations are closely related to the
thickness of the neutron skin. Approaching Sn a gradual change from a
neutron to a proton skin is found and the character of the PDR is changed
correspondingly. A delicate balance between Coulomb and strong interaction
effects is found. The fragmentation of the PDR strength in Sn is
investigated by multi-phonon calculations. Recent measurements of the dipole
response in Sn are well reproduced.Comment: 41 pages, 10 figures, PR
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