61,896 research outputs found
Revelation of double magicity in N=Z nuclei in the rp-process region
In rapid-proton capture (rp-process), N=Z nuclei above Ni are understood to
act as waiting-point nuclei. The N=Z nuclei 68Se, 72Kr, 76Sr and 80Zr among
others are known to give rise to a large-energy x-ray flux and peaks in
abundances of these nuclei synthesized in the astrophysical rp-process.
Investigating the experimental isotope shifts in Kr isotopes near the proton
drip-line within the framework of the deformed Relativistic Hartree-Bogoliubov
theory, we have discovered that N=Z rp-process nuclei 68Se, 72Kr, 76Sr and 80Zr
exhibit large shell gap both at the proton and neutron numbers in the deformed
space with the consequence that pairing correlations for protons and neutrons
vanish. This lends a doubly magic character to these nuclei. A significant
number of nuclei in this region are also shown to exhibit neutron magicity at
N=34, 36, 38, and 40 in the deformed space. A unique case of concomitance of
the double magicity and the shape-coexistence is found for 68Se.Comment: 10 pages, 4 figures; Invited contribution presented at the
International Symposium on Exotic Nuclei, EXON 2009, Sochi, Russia, Sept.
28-Oct. 2, 200
Elastic response of filamentous networks with compliant crosslinks
Experiments have shown that elasticity of disordered filamentous networks
with compliant crosslinks is very different from networks with rigid
crosslinks. Here, we model and analyze filamentous networks as a collection of
randomly oriented rigid filaments connected to each other by flexible
crosslinks that are modeled as worm-like chains. For relatively large
extensions we allow for enthalpic stretching of crosslinks' backbones. We show
that for sufficiently high crosslink density, the network linear elastic
response is affine on the scale of the filaments' length. The nonlinear regime
can become highly nonaffine and is characterized by a divergence of the elastic
modulus at finite strain. In contrast to the prior predictions, we do not find
an asymptotic regime in which the differential elastic modulus scales linearly
with the stress, although an approximate linear dependence can be seen in a
transition from entropic to enthalpic regimes. We discuss our results in light
of the recent experiments.Comment: 10 pages, 11 figure
The origins of electromechanical indentation size effect in ferroelectrics
Metals exhibit a size-dependent hardening when subject to indentation.
Mechanisms for this phenomenon have been intensely researched in recent times.
Does such a size-effect also exist in the electromechanical behavior of
ferroelectrics?--if yes, what are the operative mechanisms? Our experiments on
BaTiO3 indeed suggest an electromechanical size-effect. We argue, through
theoretical calculations and differential experiments on another
non-ferroelectric piezoelectric (Quartz), that the phenomenon of
flexoelectricity(as opposed to dislocation activity) is responsible for our
observations. Flexoelectricity is the coupling of strain gradients to
polarization and exists in both ordinary and piezoelectric dielectrics. In
particular, ferroelectrics exhibit an unusually large flexoelectric response.Comment: in revie
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