192 research outputs found
Dangling bond energetics in carbon nitride and phosphorus carbide thin films with fullerene-like and amorphous structure
Touch uses frictional cues to discriminate flat materials
In a forced-choice task, we asked human participants to discriminate by touch alone glass plates from transparent polymethyl methacrylate (PMMA) plastic plates. While the surfaces were flat and did not exhibit geometric features beyond a few tens of nanometres, the materials differed by their molecular structures. They produced similar coefficients of friction and thermal effects were controlled. Most participants performed well above chance and participants with dry fingers discriminated the materials especially well. Current models of tactile surface perception appeal to surface topography and cannot explain our results. A correlation analysis between detailed measurements of the interfacial forces and discrimination performance suggested that the perceptual task depended on the transitory contact phase leading to full slip. This result demonstrates that differences in interfacial mechanics between the finger and a material can be sensed by touch and that the evanescent mechanics that take place before the onset of steady slip have perceptual value
Exact Solution of the Isovector Proton Neutron Pairing Hamiltonian
The complete exact solution of the T=1 neutron-proton pairing Hamiltonian is
presented in the context of the SO(5) Richardson-Gaudin model with
non-degenerate single-particle levels and including isospin-symmetry breaking
terms. The power of the method is illustrated with a numerical calculation for
Ge for a model space which is out of reach of modern
shell-model codes.Comment: To be published by Physical Review Letter
Deformations of the fermion realization of the sp(4) algebra and its subalgebras
With a view towards future applications in nuclear physics, the fermion
realization of the compact symplectic sp(4) algebra and its q-deformed versions
are investigated. Three important reduction chains of the sp(4) algebra are
explored in both the classical and deformed cases. The deformed realizations
are based on distinct deformations of the fermion creation and annihilation
operators. For the primary reduction, the su(2) sub-structure can be
interpreted as either the spin, isospin or angular momentum algebra, whereas
for the other two reductions su(2) can be associated with pairing between
fermions of the same type or pairing between two distinct fermion types. Each
reduction provides for a complete classification of the basis states. The
deformed induced u(2) representations are reducible in the action spaces of
sp(4) and are decomposed into irreducible representations.Comment: 28 pages, LaTeX 12pt article styl
A mixed-mode shell-model theory for nuclear structure studies
We introduce a shell-model theory that combines traditional spherical states,
which yield a diagonal representation of the usual single-particle interaction,
with collective configurations that track deformations, and test the validity
of this mixed-mode, oblique basis shell-model scheme on Mg. The correct
binding energy (within 2% of the full-space result) as well as low-energy
configurations that have greater than 90% overlap with full-space results are
obtained in a space that spans less than 10% of the full space. The results
suggest that a mixed-mode shell-model theory may be useful in situations where
competing degrees of freedom dominate the dynamics and full-space calculations
are not feasible.Comment: 20 pages, 8 figures, revtex 12p
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