A simple model for the quenching of pairing correlations effects in rigidly deformed rotational bands

Using Chandrasekhar's S-type coupling between rotational and intrinsic vortical modes one may simply reproduce the HFB dynamical properties of rotating nuclei within Routhian HF calculations free of pairing correlations yet constrained on the relevant so-called Kelvin circulation operator. From the analogy between magnetic and rotating systems, one derives a model for the quenching of pairing correlations with rotation, introducing a critical angular velocity -- analogous to the critical field in supraconductors -- above which pairing vanishes. Taking stock of this usual model, it is then shown that the characteristic behavior of the vortical mode angular velocity as a function of the global rotation angular velocity can be modelised by a simple two parameter formula, both parameters being completely determined from properties of the band-head (zero-spin) HFB solution. From calculation in five nuclei, the validity of this modelised Routhian approach is assessed. It is clearly shown to be very good in cases where the evolution of rotational properties is only governed by the coupling between the global rotation and the pairing-induced intrinsic vortical currents. It therefore provides a sound ground base for evaluating the importance of coupling of rotation with other modes (shape distortions, quasiparticle degrees of freedom).Comment: 10 pages, 8 figures. Submited to PR

Hartree-Fock-Bogoliubov Calculations of the Rotational Band of the Very Heavy 254^{254}No Nucleus

We report on Hartree-Fock-Bogoliubov (HFB) calculations of the ground-state rotationnal band of the heavy nucleus $^{254}$No recently observed experimentally. The calculated quadrupole deformation is consistent with the experimental value of $\beta=0.27$ and is almost constant over the whole band. We also reproduce fairly well the excitation spectra and moments of inertia of this isotope up to the maximal experimentally observed state of spin 20. The rather high stability of this nucleus against fission is illustrated by the deformation energy curve providing very high fission barriers at zero spin within the HFB and HFB plus Lipkin-Nogami formalisms. The variation of these barriers with increased angular velocities is also studied.Comment: 4 pages (LaTeX), submitted to Eur. Phys. J A, dedicated to the memory of J. Piperov

Generalized routhian calculations within the Skyrme-Hartree-Fock approximation

We consider here variational solutions in the Hartree-Fock approximation upon breaking time reversal and axial symmetries. When decomposed on axial harmonic oscillator functions, the corresponding single particle triaxial eigenstates as functions of the usual cylindrical coordinates (r, $\theta$, z) are evaluated on a mesh in r and z to be integrated within Gauss-Hermite and Gauss-Laguerre approaches and as Fourier decompositions in the angular variable $\theta$. Using an effective interaction of the Skyrme type, the Hartree-Fock hamiltonian is also obtained as a Fourier series allowing a two dimensional calculation of its matrix elements. This particular choice is shown to lead in most cases to shorter computation times compared to the usual decomposition on triaxial harmonic oscillator states. We apply this method to the case of the semi-quantal approach of large amplitude collective motion corresponding to a generalized routhian formalism and present results in the A=150 superdeformed region for the coupling of global rotation and intrinsic vortical modes in what is known after Chandrasekhar as the S-ellipsoid coupling case.Comment: LaTeX using elsart, 32 pages, 4 included figures, submitted to Nuclear Physics A (revised version

Bulk properties of rotating nuclei and the validity of the liquid drop model at finite angular momenta

Out of self-consistent semi-classical calculations performed within the so-called Extended Thomas-Fermi approach for 212 nuclei at all even angular momentum values I ranging between 0 and 80 \hbar and using the Skyrme SkM* effective force, the I-dependence of associated liquid drop model parameters has been studied. The latter have been obtained trough separate fits of the calculated values of the strong interaction as well as direct and exchange Coulomb energies. The theoretical data basis so obtained, has allowed to make a rough quantitative assessment of the variation with I of the usual volume and surface energy parameters up to spin of \sim 30-40 \hbar. As a result of the combined variation of the surface and Coulomb energies, it has been shown that this I-dependence results in a significant enhancement of the fission stability of very heavy nuclei, balancing thus partially the well-known instability due to centrifugal forces.Comment: 27 pages, LaTeX (elsart) with 13 embeded postscript figure

Period of the gamma-ray staggering in the 150Gd superdeformed region

It has been previously proposed to explain gamma-ray staggerings in the deexcitation of some superdeformed bands in the $^{150}$Gd region in terms of a coupling between global rotation and intrinsic vortical modes. The observed 4$\hbar$ period for the phenomenon is suggested from our microscopic Routhian calculations using the Skyrme SkM* effective interaction.Comment: 4 pages, LaTeX with RevTeX, 4 included figures, submitted to Phys. Rep. C (revised version

Synthèses et caractérisations physiques de matrices polymères pour la formulation de dispersions solides amorphes curcumine/polyvinylpyrrolidone

This thesis aims at improving our fundamental knowledge on the mechanisms involved in the formation of amorphous solid dispersions (ASD) of a drug within a polymer excipient, in particular the impact of the macromolecular architecture on the physical stability of ASD.Poly(N-vinylpyrrolidone) (PVP) polymers with low dispersity and different molar masses and chain-end functionalities are first synthesised in a controlled manner by RAFT/MADIX (Reversible Addition-Fragmentation chain Transfer/ Macromolecular design by Interchange of Xanthates). They are then used to formulate, by co-milling and solvent evaporation processes, mixtures with curcumin (CUR). The advanced physico-chemical characterisation of PVP, CUR and the obtained ASD enables us to establish the CUR/PVP phase (solubility limit) and state (glass transition temperature (Tg) evolution) diagrams. On the one hand, this diagram allows us to better understand the stability conditions of CUR/PVP ASD and the impact of the PVP molar mass and chain-end functionality. On the other hand, comparison with ASD formulated with high dispersity commercial PVP allows us to highlight the specific role of the dispersity on the Tg of PVP and of CUR/PVP ASD. Indeed, for ASD formulated with high dispersity PVP, results show the decrease of Tg at high PVP contents, which unveils a competition between the development of attractive interactions between CUR and PVP and a plasticising effect induced by the broad distribution of PVP molar masses. Finally, this work reveals that the use of PVP synthesised in a controlled manner allows to obtain stable ASD over a broader range of temperatures and CUR concentrations than for ASD formulated with industrially available PVP of high dispersity.L'objectif de ce travail de thèse est d'améliorer la connaissance fondamentale des mécanismes intervenant dans la formation de dispersions solides amorphes (DSA) d'un principe actif pharmaceutique au sein d'un excipient polymère, en particulier l'impact de l'architecture macromoléculaire des polymères sur la stabilité physique des DSA.Des polymères de poly(N-vinylpyrrolidone) (PVP) de faible dispersité, de masses molaires et fonctionnalités d'extrémités de chaînes différentes sont d'abord synthétisés de façon contrôlée par RAFT/MADIX (Reversible Addition-Fragmentation chain Transfer/ Macromolecular design by Interchange of Xanthates). Ils sont ensuite utilisés pour la formulation, par co-broyage et évaporation de solvant, de mélanges à base de curcumine (CUR). La caractérisation physico-chimique avancée du PVP, de la CUR et des DSA obtenues nous permet d'établir le diagramme de phases (courbe de solubilité) et d'états (évolution de la température de transition vitreuse (Tg)) CUR/PVP. Ce diagramme permet, d'une part, de mieux comprendre les conditions de stabilité des DSA CUR/PVP et l'impact de la masse molaire ou de la fonctionnalité des extrémités de chaînes du PVP. D'autre part, la comparaison avec des DSA formulées avec du PVP commercial de forte dispersité nous permet d'établir le rôle particulier de la dispersité sur la Tg du PVP et celle des DSA CUR/PVP. En effet, dans le cas de DSA formulées avec du PVP de forte dispersité, les résultats montrent une diminution de Tg pour des taux élevés de PVP qui dévoile une compétition entre le développement d'interactions attractives entre CUR et PVP et un effet plastifiant engendré par la grande distribution des masses molaires du PVP. Enfin, ce travail révèle que l'utilisation de PVP synthétisés de façon contrôlée permet d'obtenir des DSA stables sur un domaine de températures et de concentrations en curcumine plus étendu que pour des DSA formulées avec un PVP industriel de forte dispersité