6,294 research outputs found
Influence of pairing correlations on the radius of neutron-rich nuclei
The influence of pairing correlations on the neutron root mean square (rms)
radius of nuclei is investigated in the framework of self-consistent Skyrme
Hartree-Fock-Bogoliubov calculations. The continuum is treated appropriately by
the Green's function techniques. As an example the nucleus Zr is
treated for a varying strength of pairing correlations. We find that, as the
pairing strength increases, the neutron rms radius first shrinks, reaches a
minimum and beyond this point it expands again. The shrinkage is due to the the
so-called `pairing anti-halo effect', i. e. due to the decreasing of the
asymptotic density distribution with increasing pairing. However, in some
cases, increasing pairing correlations can also lead to an expansion of the
nucleus due to a growing occupation of so-called `halo' orbits, i.e. weakly
bound states and resonances in the continuum with low- values. In this
case, the neutron radii are extended just by the influence of pairing
correlations, since these `halo' orbits cannot be occupied without pairing. The
term `anti-halo effect' is not justified in such cases. For a full
understanding of this complicated interplay self-consistent calculations are
necessary.Comment: 18 pages, 5 figure
Perturbative interpretation of relativistic symmetries in nuclei
Perturbation theory is used systematically to investigate the symmetries of
the Dirac Hamiltonian and their breaking in atomic nuclei. Using the
perturbation corrections to the single-particle energies and wave functions,
the link between the single-particle states in realistic nuclei and their
counterparts in the symmetry limits is discussed. It is shown that the limit of
S-V=const and relativistic harmonic oscillator (RHO) potentials can be
connected to the actual Dirac Hamiltonian by the perturbation method, while the
limit of S+V=const cannot, where S and V are the scalar and vector potentials,
respectively. This indicates that the realistic system can be treated as a
perturbation of spin-symmetric Hamiltonians, and the energy splitting of the
pseudospin doublets can be regarded as a result of small perturbation around
the Hamiltonian with RHO potentials, where the pseudospin doublets are
quasidegenerate.Comment: 5 pages, 4 figures, Phys. Rev. C in pres
Nuclear matter properties with nucleon-nucleon forces up to fifth order in the chiral expansion
The properties of nuclear matter are studied using state-of-the-art
nucleon-nucleon forces up to fifth order in chiral effective field theory. The
equations of state of symmetric nuclear matter and pure neutron matter are
calculated in the framework of the Brueckner-Hartree-Fock theory. We discuss in
detail the convergence pattern of the chiral expansion and the regulator
dependence of the calculated equations of state and provide an estimation of
the truncation uncertainty. For all employed values of the regulator, the
fifth-order chiral two-nucleon potential is found to generate nuclear
saturation properties similar to the available phenomenological high precision
potentials. We also extract the symmetry energy of nuclear matter, which is
shown to be quite robust with respect to the chiral order and the value of the
regulator.Comment: 10 pages, 3 figures, 3 table
Outage analysis of superposition modulation aided network coded cooperation in the presence of network coding noise
We consider a network, where multiple sourcedestination pairs communicate with the aid of a half-duplex relay node (RN), which adopts decode-forward (DF) relaying and superposition-modulation (SPM) for combining the signals transmitted by the source nodes (SNs) and then forwards the composite signal to all the destination nodes (DNs). Each DN extracts the signals transmitted by its own SN from the composite signal by subtracting the signals overheard from the unwanted SNs. We derive tight lower-bounds for the outage probability for transmission over Rayleigh fading channels and invoke diversity combining at the DNs, which is validated by simulation for both the symmetric and the asymmetric network configurations. For the high signal-to-noise ratio regime, we derive both an upperbound as well as a lower-bound for the outage performance and analyse the achievable diversity gain. It is revealed that a diversity order of 2 is achieved, regardless of the number of SN-DN pairs in the network. We also highlight the fact that the outage performance is dominated by the quality of the worst overheated link, because it contributes most substantially to the network coding noise. Finally, we use the lower bound for designing a relay selection scheme for the proposed SPM based network coded cooperative communication (SPM-NC-CC) system.<br/
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