Extensive systematizations of theoretical and experimental nuclear densities and of optical potential strengths extracted from heavy-ion elastic scattering data analyses at low and intermediate energies are presented. The energy dependence of the nuclear potential is accounted for within a model based on the nonlocal nature of the interaction. The systematics indicates that the heavy-ion nuclear potential can be described in a simple global way through a double-folding shape, which basically depends only on the density of nucleons of the partners in the collision. The possibility of extracting information about the nucleon-nucleon interaction from the heavy-ion potential is investigated.

We make a careful study about the nonrelativistic reduction of one-meson-exchange models for the nonmesonic weak hypernuclear decay. Starting from a widely accepted effective coupling Hamiltonian involving the exchange of the complete pseudoscalar and vector meson octets (π, η, K, ρ, ω, K * ), the strangeness-changing weak ΛN → N N transition potential is derived, including two effects that have been systematically omitted in the literature, or, at best, only partly considered. These are the kinematical effects due to the difference between the lambda and nucleon masses, and the first-order nonlocality corrections, i.e., those involving up to first-order differential operators. Our analysis clearly shows that the main kinematical effect on the local contributions is the reduction of the effective pion mass. The kinematical effect on the nonlocal contributions is more complicated, since it activates several new terms that would otherwise remain dormant. Numerical results for 12 Λ C and 5 Λ He are presented and they show that the combined kinematical plus nonlocal corrections have an appreciable influence on the partial decay rates. However, this is somewhat diminished in the main decay observables: the total nonmesonic rate, Γ nm , the neutron-to-proton branching ratio, Γ n /Γ p , and the asymmetry parameter, a Λ . The latter two still cannot be reconciled with the available experimental data. The existing theoretical predictions for the sign of a Λ in 5 Λ He are confirmed.The free decay of a Λ hyperon occurs almost exclusively through the mesonic mode, Λ → πN , with the nucleon emerging with a momentum of about 100 MeV/c. Inside nuclear matter (p F ≈ 270 MeV/c) this mode is Pauli blocked, and, for all but the lightest Λ hypernuclei (A ≥ 5), the weak decay is dominated by the nonmesonic channel, ΛN → N N , which liberates enough kinetic energy to put the two emitted nucleons above the Fermi surface. In the absence of stable hyperon beams, these nonmesonic decays offer the only way available to investigate the strangeness-changing weak interaction between hadrons. (For reviews on hypernuclear decay, see Refs.[1]- [3].) The simplest model for this process is the exchange of a virtual pion [4], and in fact this can reproduce reasonably well the total (nonmesonic) decay rate, Γ nm = Γ n + Γ p , but fails badly for other observables like the ratio of neutron-induced (Λn → nn) to proton-induced (Λp → np) transitions, Γ n /Γ p , and the asymmetry parameter a Λ . The deficiency of this model is attributed to effects of short range physics, which should be quite important in view of the large momentum transfers involved (∼ 400 MeV/c). Although there have been some attempts to account for this fact by making use of quark models to compute the shortest range part of the transition potential [5]-[9], most of the theoretical work opted for the addition of other, heavier mesons in the exchange process [10]- [23]. None of these models gives fully satisfactory results. Inclusion of correlated two-pion exchange has not been comple...

We study medium modifications of the nucleon-nucleon (NN) cross sections and their influence on the nucleon knockout reactions. Using the eikonal approximation, we compare the results obtained with free NN cross sections with those obtained with a purely geometrical treatment of Pauli blocking and with NN obtained with more elaborated Dirac-Bruecker methods. The medium effects are parametrized in terms of the baryon density. We focus on symmetric nuclear matter, although the geometrical Pauli blocking also allows for the treatment of asymmetric nuclear matter. It is shown that medium effects can change the nucleon knockout cross sections and momentum distributions up to 10% in the energy range E lab = 50-300 MeV/nucleon. The effect is more evident in reactions involving halo nuclei.

Disorder is emerging as a strategy for fabricating random laser sources with very promising materials, such as perovskites, for which standard laser cavities are not effective or too expensive. We need, however, different fabrication protocols and technologies for reducing the laser threshold and controlling its emission. Here, we demonstrate an effectively solvent-engineered method for high-quality perovskite thin films on a flexible polyimide substrate. The fractal perovskite thin films exhibit excellent optical properties at room temperature and easily achieve lasing action without any laser cavity above room temperature with a low pumping threshold. The lasing action is also observed in curved perovskite thin films on flexible substrates. The lasing threshold can be further reduced by increasing the local curvature, which modifies the scattering strengths of the bent thin film. We also show that the curved perovskite lasers are extremely robust with respect to repeated deformations. Because of the low spatial coherence, these curved random laser devices are efficient and durable speckle-free light sources for applications in spectroscopy, bioimaging, and illumination.

Precise elastic scattering differential cross sections have been measured for the 12 Cϩ 58 Ni, 208 Pb systems at sub-barrier energies. The corresponding bare potentials have been determined at interaction distances larger than the respective barrier radii, and the results have been compared with those from an early extensive systematics for the nuclear potential. The present data have been combined with others for the 12 C ϩ 12 C, 208 Pb systems at intermediate energies, in order to extract the 12 C ground-state nuclear density through an unfolding method.