72,299 research outputs found
Projector operators for the no-core shell model
Projection operators for the use within ab initio no-core shell model, are
suggested.Comment: 3 page
Test of shell-model interactions for nuclear structure calculations
The binding energy and excitation spectra of 6Li are calculated in a no-core shell-model space giving encouraging results. The results of this calculation are then treated as a theoretical experiment, against which different effective-interaction approximations are compared. In this way insight into the perturbation expansion for the effective interaction is obtained
Quasiperiodic, periodic, and slowing-down states of coupled heteroclinic cycles
We investigate two coupled oscillators, each of which shows an attracting heteroclinic cycle in the absence of coupling. The two heteroclinic cycles are nonidentical. Weak coupling can lead to the elimination of the slowing-down state that asymptotically approaches the heteroclinic cycle for a single cycle, giving rise to either quasiperiodic motion with separate frequencies from the two cycles or periodic motion in which the two cycles are synchronized. The synchronization transition, which occurs via a Hopf bifurcation, is not induced by the commensurability of the two cycle frequencies but rather by the disappearance of the weaker frequency oscillation. For even larger coupling the motion changes via a resonant heteroclinic bifurcation to a slowing-down state corresponding to a single attracting heteroclinic orbit. Coexistence of multiple attractors can be found for some parameter regions. These results are of interest in ecological, sociological, neuronal, and other dynamical systems, which have the structure of coupled heteroclinic cycles
First-principles study of the effects of gold adsorption on the Al(001) surface properties
In this work, we have studied theoretically the effects of gold adsorption on
the Al(001) surface, using {\it ab initio} pseudo-potential method in the
framework of the density functional theory. Having found the hollow sites at
the Al(001) surface as the most preferred adsorption sites, we have
investigated the effects of the Au adsorption with different coverages
(=0.11, 0.25, 0.50, 0.75, 1.00 ML) on the geometry, adsorption energy,
surface dipole moment, and the work-function of the Al(001) surface. The
results show that, even though the work-function of the Al substrate increases
with the Au coverage, the surface dipole moment decreases with the changes in
coverage from ML to ML. We have explained this
behavior by analyzing the electronic and ionic charge distributions.
Furthermore, by studying the diffusion of Au atoms in to the substrate, we have
shown that at room temperature the diffusion rate of Au atoms in to the
substrate is negligible but, increasing the temperature to about 200 C
the Au atoms significantly diffuse in to the substrate, in agreement with the
experiment.Comment: 19 pages, 9 eps figure
Universality and correlations in individuals wandering through an online extremist space
The 'out of the blue' nature of recent terror attacks and the diversity of
apparent motives, highlight the importance of understanding the online
trajectories that individuals follow prior to developing high levels of
extremist support. Here we show that the physics of stochastic walks, with and
without temporal correlation, provides a unifying description of these online
trajectories. Our unique dataset comprising all users of a global social media
site, reveals universal characteristics in individuals' online lifetimes. Our
accompanying theory generates analytical and numerical solutions that describe
the characteristics shown by individuals that go on to develop high levels of
extremist support, and those that do not. The existence of these temporal and
also many-body correlations suggests that existing physics machinery can be
used to quantify and perhaps mitigate the risk of future events
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