The Isovector Quadrupole-Quadrupole Interaction Used in Shell Model Calculations

An interaction $-\chi Q\cdot Q(1+B\vec{\tau}(1)\cdot \vec{\tau}(2))$ is used in a shell model calculation for $^{10}Be$. Whereas for $B=0$ the $2_1^+$ state is two-fold degenerate, introducing a negative $B$ causes an `isovector' $2^+$ state to come down to zero energy at $B=-0.67$ and an $S=1~L=1$ triplet ($J=0^+,~1^+,~2^+$) to come down to zero energy at $B=-0.73$. These are undesirable properties, but a large negative $B$ is apparently needed to fit the energy of the isovector giant quadrupole resonance.Comment: 12 pages, revtex, 2 figures (available on request

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

Effects of benzene and several pharmaceuticals on the growth and microcystin production in Microcystis ruginosa PCC 7806

Currently, the presence of several pharmaceuticals and other organic compounds called ‘emerging’ contaminants has increased in water bodies. These compounds do not need to persist in the environment to cause negative effects because they are continuously introduced. Hence, assessing the effects of these compounds on aquatic ecosystems is essential. Therefore, the aim of the present study was to analyse the effects of several emerging contaminants (ibuprofen, atenolol, diclofenac and paracetamol) and benzene on Microcystis aeruginosa PCC 7806 growth and toxicity. For this purpose, the growth and intracellular microcystin concentration in M. aeruginosa PCC 7806 were measured in presence of the four emerging contaminants and benzene. The growth rate was estimated by chlorophyll a concentration, and no relevant changes were found. Changes in the expression of the operon mcy were examined by semi-quantitative RT-PCR. Intracellular microcystin production was determined using a MicroCystest¿R kit, and no changes were observed compared to control cells. Thus, the tested concentrations of the contaminants analysed in this study do not have a significant effect on microcystin production in this strain under laboratory conditions

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