Structure of the vacuum states in the presence of isovector and isoscalar pairing correlations

The long standing problem of proton-neutron pairing and, in particular, the limitations imposed on the solutions by the available symmetries, is revisited. We look for solutions with non-vanishing expectation values of the proton, the neutron and the isoscalar gaps. For an equal number of protons and neutrons we find two solutions where the absolute values of proton and neutrons gaps are equal but have the same or opposite sign. The behavior and structure of these solutions differ for spin saturated (single l-shell) and spin unsaturared systems (single j-shell). In the former case the BCS results are checked against an exact calculation.Comment: 19 pages, 5 postscript figure

Spin distribution of nuclear levels using static path approximation with random-phase approximation

We present a thermal and quantum-mechanical treatment of nuclear rotation using the formalism of static path approximation (SPA) plus random-phase approximation (RPA). Naive perturbation theory fails because of the presence of zero-frequency modes due to dynamical symmetry breaking. Such modes lead to infrared divergences. We show that composite zero-frequency excitations are properly treated within the collective coordinate method. The resulting perturbation theory is free from infrared divergences. Without the assumption of individual random spin vectors, we derive microscopically the spin distribution of the level density. The moment of inertia is thereby related to the spin-cutoff parameter in the usual way. Explicit calculations are performed for 56^Fe; various thermal properties are discussed. In particular, we demonstrate that the increase of the moment of inertia with increasing temperature is correlated with the suppression of pairing correlations.Comment: 12 pages, 8 figures, accepted for publication in Physical Review

Expression of TLP-3 gene without signal peptide in tobacco plants using Agrobacterium mediated transformation

Plants are exploited as a source of food by a wide range of parasites, including viruses, bacteria, fungi, nematodes, insects and even other plants. So paying attention to their protection is very important. One of the most important groups of defensive gene is pathogenesis-related (PR) proteins. PR proteins are a group of plant proteins which accumulate as a result of different types of pathogens attack. Thaumatinlike proteins (TLPs) belonging to the PR proteins, plays an important role in plant defense against pathogen invasions. Agrobacterium-mediated transformation is routinely used for the transformation of many plants. In the present study, thaumatin-like TLP-3 gene without signal peptide was transferred into tobacco plants through Agrobacterium-mediated technology. The PCR and RT-PCR assays confirmed the presence of TLP-3 gene and TLP-3 mRNA in transgenic tobacco plants, respectively. The bioassay results showed the activity of TLP-3 against Alternaria alternata in microscopic experiment. This is the first report of the expression of TLP-3 gene without signal peptide in tobacco plants using Agrobacterium mediated transformation and it confirmed the ability of the gene action in another plant.Key words: Thaumatin like protein, Agrobacterium, signal peptide, Alternaria alternate

Triaxial quadrupole deformation dynamics in sd-shell nuclei around 26Mg

Large-amplitude dynamics of axial and triaxial quadrupole deformation in 24,26Mg, 24Ne, and 28Si is investigated on the basis of the quadrupole collective Hamiltonian constructed with use of the constrained Hartree-Fock-Bogoliubov plus the local quasiparticle random phase approximation method. The calculation reproduces well properties of the ground rotational bands, and beta and gamma vibrations in 24Mg and 28Si. The gamma-softness in the collective states of 26Mg and 24Ne are discussed. Contributions of the neutrons and protons to the transition properties are also analyzed in connection with the large-amplitude quadrupole dynamics.Comment: 16 pages, 18 figures, submitted to Phys. Rev.

Many-body effects in nuclear structure

We calculate, for the first time, the state-dependent pairing gap of a finite nucleus (120Sn) diagonalizing the bare nucleon-nucleon potential (Argonne v14) in a Hartree-Fock basis (with effective k-mass m_k eqult to 0.7 m), within the framework of the BCS approximation including scattering states up to 800 MeV above the Fermi energy to achieve convergence. The resulting gap accounts for about half of the experimental gap. We find that a consistent description of the low-energy nuclear spectrum requires, aside from the bare nucleon-nucleon interaction, not only the dressing of single-particle motion through the coupling to the nuclear surface, to give the right density of levels close to the Fermi energy (and thus an effective mass m* approximately equal to m), but also the renormalization of collective vibrational modes through vertex and self-energy processes, processes which are also found to play an essential role in the pairing channel, leading to a long range, state dependent component of the pairing interaction. The combined effect of the bare nucleon-nucleon potential and of the induced pairing interaction arising from the exchange of low-lying surface vibrations between nucleons moving in time reversal states close to the Fermi energy accounts for the experimental gap.Comment: 5 pages, 4 figures; author list correcte

Study of Giant Pairing Vibrations with neutron-rich nuclei

We investigate the possible signature of the presence of giant pairing states at excitation energy of about 10 MeV via two-particle transfer reactions induced by neutron-rich weakly-bound projectiles. Performing particle-particle RPA calculations on $^{208}$Pb and BCS+RPA calculations on $^{116}$Sn, we obtain the pairing strength distribution for two particles addition and removal modes. Estimates of two-particle transfer cross sections can be obtained in the framework of the 'macroscopic model'. The weak-binding nature of the projectile kinematically favours transitions to high-lying states. In the case of (~^6He, \~^4He) reaction we predict a population of the Giant Pairing Vibration with cross sections of the order of a millibarn, dominating over the mismatched transition to the ground state.Comment: Talk presented in occasion of the VII School-Semina r on Heavy Ion Physics hosted by the Flerov Laboratory (FLNR/JINR) Dubna, Russia from May 27 to June 2, 200

Microscopic description of large-amplitude shape-mixing dynamics with inertial functions derived in local quasiparticle random-phase approximation

On the basis of the adiabatic self-consistent collective coordinate method, we develop an efficient microscopic method of deriving the five-dimensional quadrupole collective Hamiltonian and illustrate its usefulness by applying it to the oblate-prolate shape coexistence/mixing phenomena in proton-rich 68,70,72Se. In this method, the vibrational and rotational collective masses (inertial functions) are determined by local normal modes built on constrained Hartree-Fock-Bogoliubov states. Numerical calculations are carried out using the pairing-plus-quadrupole Hamiltonian including the quadrupole-pairing interaction. It is shown that the time-odd components of the moving mean-field significantly increase the vibrational and rotational collective masses in comparison with the Inglis-Belyaev cranking masses. Solving the collective Schroedinger equation, we evaluate excitation spectra, quadrupole transitions and moments. Results of the numerical calculation are in excellent agreement with recent experimental data and indicate that the low-lying states of these nuclei are characterized as an intermediate situation between the oblate-prolate shape coexistence and the so-called gamma unstable situation where large-amplitude triaxial-shape fluctuations play a dominant role.Comment: 17 pages, 16 figures, Submitted to Phys. Rev.