944 research outputs found
Critical densities for the Skyrme type effective interactions
We use the stability conditions of the Landau parameters for the symmetric
nuclear matter and pure neutron matter to calculate the critical densities for
the Skyrme type effective nucleon-nucleon interactions. We find that the
critical density can be maximized by adjusting appropriately the values of the
enhancement factor associated with isovector giant dipole resonance,
the quantity which is directly related to the slope of the symmetry energy
and the Landau parameter . However, restricting , and
to vary within acceptable limits reduces the maximum value for the
critical density by . We also show that among the
various quantities characterizing the symmetric nuclear matter,
depends strongly on the isoscalar effective mass and
surface energy coefficient . For realistic values of and we
get to (fm).Comment: 10 pages, 3 figures. Physicsl Review C (in press
Scaling of the distribution of shortest paths in percolation
We present a scaling hypothesis for the distribution function of the shortest
paths connecting any two points on a percolating cluster which accounts for
{\it (i)} the effect of the finite size of the system, and {\it (ii)} the
dependence of this distribution on the site occupancy probability . We test
the hypothesis for the case of two-dimensional percolation.Comment: 7 pages, 3 figure
Secure Degrees of Freedom of MIMO X-Channels with Output Feedback and Delayed CSIT
We investigate the problem of secure transmission over a two-user multi-input
multi-output (MIMO) X-channel in which channel state information is provided
with one-unit delay to both transmitters (CSIT), and each receiver feeds back
its channel output to a different transmitter. We refer to this model as MIMO
X-channel with asymmetric output feedback and delayed CSIT. The transmitters
are equipped with M-antennas each, and the receivers are equipped with
N-antennas each. For this model, accounting for both messages at each receiver,
we characterize the optimal sum secure degrees of freedom (SDoF) region. We
show that, in presence of asymmetric output feedback and delayed CSIT, the sum
SDoF region of the MIMO X-channel is same as the SDoF region of a two-user MIMO
BC with 2M-antennas at the transmitter, N-antennas at each receiver and delayed
CSIT. This result shows that, upon availability of asymmetric output feedback
and delayed CSIT, there is no performance loss in terms of sum SDoF due to the
distributed nature of the transmitters. Next, we show that this result also
holds if only output feedback is conveyed to the transmitters, but in a
symmetric manner, i.e., each receiver feeds back its output to both
transmitters and no CSIT. We also study the case in which only asymmetric
output feedback is provided to the transmitters, i.e., without CSIT, and derive
a lower bound on the sum SDoF for this model. Furthermore, we specialize our
results to the case in which there are no security constraints. In particular,
similar to the setting with security constraints, we show that the optimal sum
DoF region of the (M,M,N,N)--MIMO X-channel with asymmetric output feedback and
delayed CSIT is same as the DoF region of a two-user MIMO BC with 2M-antennas
at the transmitter, N-antennas at each receiver, and delayed CSIT. We
illustrate our results with some numerical examples.Comment: To Appear in IEEE Transactions on Information Forensics and Securit
Determination of the parameters of a Skyrme type effective interaction using the simulated annealing approach
We implement for the first time the simulated annealing method (SAM) to the
problem of searching for the global minimum in the hyper-surface of the
chi-square function which depends on the values of the parameters of a Skyrme
type effective nucleon-nucleon interaction. We undertake a realistic case of
fitting the values of the Skyrme parameters to an extensive set of experimental
data on the ground state properties of many nuclei ranging from normal to
exotic ones. The set of experimental data used in our fitting procedure
includes the radii for the valence and neutron orbits in
the O and Ca nuclei, respectively, and the breathing mode
energies for several nuclei, in addition to the typically used data on binding
energy, charge radii and spin-orbit splitting. We also include in the fit the
critical density and further constrain the values of the Skyrme
parameters by requiring that (i) the quantity ,
directly related to the slope of the symmetry energy , must be positive for
densities up to (ii) the enhancement factor , associated with
the isovector giant dipole resonance, should lie in the range of
and (iii) the Landau parameter is positive at . We
provide simple but consistent schemes to account for the center of mass
corrections to the binding energy and charge radii.Comment: 33 pages, 4 figures, Phys. Rev. C (in press
Possible Connection between the Optimal Path and Flow in Percolation Clusters
We study the behavior of the optimal path between two sites separated by a
distance on a -dimensional lattice of linear size with weight
assigned to each site. We focus on the strong disorder limit, i.e., when the
weight of a single site dominates the sum of the weights along each path. We
calculate the probability distribution of the optimal
path length , and find for a power law decay with
, characterized by exponent . We determine the
scaling form of in two- and three-dimensional lattices.
To test the conjecture that the optimal paths in strong disorder and flow in
percolation clusters belong to the same universality class, we study the tracer
path length of tracers inside percolation through their
probability distribution . We find that, because the
optimal path is not constrained to belong to a percolation cluster, the two
problems are different. However, by constraining the optimal paths to remain
inside the percolation clusters in analogy to tracers in percolation, the two
problems exhibit similar scaling properties.Comment: Accepted for publication to Physical Review E. 17 Pages, 6 Figures, 1
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