Relativistic Hartree-Bogoliubov theory with finite range pairing forces in coordinate space: Neutron halo in light nuclei

The Relativistic Hartree Bogoliubov (RHB) model is applied in the self-consistent mean-field approximation to the description of the neutron halo in the mass region above the s-d shell. Pairing correlations and the coupling to particle continuum states are described by finite range two-body forces. Finite element methods are used in the coordinate space discretization of the coupled system of Dirac-Hartree-Bogoliubov integro-differential eigenvalue equations, and Klein-Gordon equations for the meson fields. Calculations are performed for the isotopic chains of Ne and C nuclei. We find evidence for the occurrence of neutron halo in heavier Ne isotopes. The properties of the 1f-2p orbitals near the Fermi level and the neutron pairing interaction play a crucial role in the formation of the halo. Our calculations display no evidence for the neutron halo phenomenon in C isotopes.Comment: 7 pages, Latex, 5 P.S. Figures, To appear in Phys. Rev. Let

Mass ingestion of gastroliths and other foreign bodies in three juvenile hooded seals (Cystophora cristata) stranded in north-western Iberian Peninsula

We present here three clinical cases involving mass ingestion of foreign bodies in Hooded seals (Cystophora cristata) stranded in north-western Iberian Peninsula. Although the presence of gastroliths is considered to be normal in pinnipeds, the cases presented here highlight how an excessive presence of them as well as other foreign bodies could result in rapid onset of a potentially lethal gastrointestinal stasis syndrome, which has to be quickly resolved, medically or surgically. Ultrasound examinations and posterior X-ray confirmation have demonstrated their utility to a rapid detection of gastric bodies, and have to be taken into account in Hooded seal routine clinical protocols. Finally, we conclude that it is particularly important to avoid the use of loose stones or sand over resting areas and to take extreme precautions with small items near the rehabilitation pools when dealing with this seal species.JM Alonso-Farré and M. Llarena-Reino are currently funded by Fundação para a Ciência e a Tecnologia, (Portugal), under post-doctoral fellowship SFRH/BPD/47251/2008, and pre-doctoral grant SFRH/BD/45398/2008, respectively.Peer reviewe

Influence of surface coating on the intracellular behaviour of gold nanoparticles : a fluorescence correlation spectroscopy study

In the biomedical applications of nanoparticles (NPs), the proper choice of surface chemistry is a crucial aspect in their design. The nature of the coating can heavily impact the interaction of NPs with biomolecules, affect the state of aggregation, and ultimately determine their biological fate. As such, protein corona formation and the aggregation behaviour of gold NPs (Au NPs) are studied here. Au NPs are prepared with four distinct surface functionalisations, namely mercaptosuccinic acid (MSA), N-4-thiobutyroil glucosamine, HS-PEG5000 and HS-alkyl-PEG600. Corona formation, aggregation, and the intracellular behaviour of the Au NPs are then investigated by means of Fluorescence Correlation Spectroscopy (FCS) in cell culture media and in live cells. To evaluate the state of aggregation and the formation of a protein corona, the Au NPs are incubated in cell media and the diffusion coefficient is determined via FCS. The in vitro behaviour is compared with the level of aggregation of the NPs in cells. Diffusion times of the NPs are estimated at different positions in the cell after a one hour incubation period. It is found that the majority of MSA and glucose-Au NPs are present inside the cell as slowly diffusing species with diffusion times (\u3c4D) greater than 6000 \u3bcs (hydrodynamic diameter >250 nm). PEGylated Au NPs adsorb a small amount of protein and manifest low agglomeration both in media and in living cells. In particular, the HS-alkyl-PEG600 coating shows an excellent correlation between lower protein adsorption, 4-fold lower compared to the MSA coated NPs, and limited intracellular aggregation. In the case of single HS-alkyl-PEG600 coated NPs, it is found that typical intracellular \u3c4D values range from 500 to 1500 \u3bcs, indicating that these particles display reduced aggregation in the intracellular environment

A Dirac-Hartree-Bogoliubov approximation for finite nuclei

We develop a complete Dirac-Hartree-Fock-Bogoliubov approximation to the ground state wave function and energy of finite nuclei. We apply it to spin-zero proton-proton and neutron-neutron pairing within the Dirac-Hartree-Bogoliubov approximation (we neglect the Fock term), using a zero-range approximation to the relativistic pairing tensor. We study the effects of the pairing on the properties of the even-even nuclei of the isotopic chains of Ca, Ni and Sn (spherical) and Kr and Sr (deformed), as well as the $N$=28 isotonic chain, and compare our results with experimental data and with other recent calculations.Comment: 43 pages, RevTex, 13 figure

Shell Effects in Nuclei with Vector Self-Coupling of Omega Meson in Relativistic Hartree-Bogoliubov Theory

Shell effects in nuclei about the stability line are investigated within the framework of the Relativistic Hartree-Bogoliubov (RHB) theory with self-consistent finite-range pairing. Using 2-neutron separation energies of Ni and Sn isotopes, the role of $\sigma$- and $\omega$-meson couplings on the shell effects in nuclei is examined. It is observed that the existing successful nuclear forces (Lagrangian parameter sets) based upon the nonlinear scalar coupling of $\sigma$-meson exhibit shell effects which are stronger than suggested by the experimental data. We have introduced nonlinear vector self-coupling of $\omega$-meson in the RHB theory. It is shown that the inclusion of the vector self-coupling of $\omega$-meson in addition to the nonlinear scalar coupling of $\sigma$-meson provides a good agreement with the experimental data on shell effects in nuclei about the stability line. A comparison of the shell effects in the RHB theory is made with the Hartree-Fock Bogoliubov approach using the Skyrme force SkP. It is shown that the oft-discussed shell quenching with SkP is not consistent with the available experimental data.Comment: 34 pages latex, 18 ps figures, replaced with minor corrections in some figures, accepted for publication in Phys. Rev.

Continuum effects for the mean-field and pairing properties of weakly bound nuclei

Continuum effects in the weakly bound nuclei close to the drip-line are investigated using the analytically soluble Poschl-Teller-Ginocchio potential. Pairing correlations are studied within the Hartree-Fock-Bogoliubov method. We show that both resonant and non-resonant continuum phase space is active in creating the pairing field. The influence of positive-energy phase space is quantified in terms of localizations of states within the nuclear volume.Comment: 27 RevTeX pages, 12 EPS figures included, submitted to Physical Review

Recensions

A.G. LUCIANI, Il mito di Prometeo e altri sagg

Recensions

A.G. LUCIANI, Il mito di Prometeo e altri sagg