Towards Sustainable Food Security

Text of the Sir John Crawford Memorial Lecture delivered during CGIAR International Centers Week, October 1993 by James Gustave Speth, UN Development Program Administrator. Speth emphasized the importance of involving the rural poor directly in poverty reduction and agricultural development programs, and the centrality of sustainability and food security to these issues. He identified a central role in these problems for the CGIAR

Optimizing phonon space in the phonon-coupling model

We present a new scheme to select the most relevant phonons in the phonon-coupling model, named here time-blocking approximation (TBA). The new criterion, based on the phonon-nucleon coupling strengths rather than on $B(EL)$ values, is more selective and thus produces much smaller phonon spaces in TBA. This is beneficial in two respects: first, it curbs down the computational cost, and second, it reduces the danger of double counting in the expansion basis of TBA. We use here TBA in a form where the coupling strength is regularized to keep the given Hartree-Fock ground state stable. The scheme is implemented in an RPA and TBA code based on the Skyrme energy functional. We first explore carefully the cutoff dependence with the new criterion and can work out a natural (optimal) cutoff parameter. Then we use the freshly developed and tested scheme to a survey of giant resonances and low-lying collective states in six doubly magic nuclei looking also on the dependence of the results when varying the Skyrme parametrization.Comment: 9 figures, 3 table

Self-consistency in the phonon space of the particle-phonon coupling model

In the paper the non-linear generalization of the time blocking approximation (TBA) is presented. The TBA is one of the versions of the extended random-phase approximation (RPA) developed within the Green-function method and the particle-phonon coupling model. In the generalized version of the TBA the self-consistency principle is extended onto the phonon space of the model. The numerical examples show that this non-linear version of the TBA leads to the convergence of the results with respect to enlarging the phonon space of the model.Comment: 12 pages, 10 figures, 1 tabl

Final state interactions and NNNN correlations: are the latter observable?

Are effects of short range correlations in the ground state of the target nucleus (initial state correlations ISC) observable in experiments on quasielastic $A(e,e'p)$ scattering at large missing momentum $p_{m}$? Will the missing momentum spectrum observed at CEBAF be overwhelmed by final state interactions (FSI) of the struck proton? The recent advances in the theory of FSI and findings of complex interplay and strong quantum-mechanical interference of FSI and ISC contributions to scattering at p_{m}\gsim 1\,fm$^{-1}$ are reviewed. We conclude that for p_m \gsim 1 \, fm$^{-1}$ quasielastic scattering is dominated by FSI effects and the sensitivity to details of the nuclear ground state is lost.Comment: Invited Talk given by N.N.Nikolaev at the Conference on Perspectives in Nuclear Physics at Intermediate Energies (Trieste, Italy, May 1995) 18 pages, uuencoded including all figure

Landau-Migdal vs. Skyrme

The magnitude and density-dependence of the non-spin dependent Landau-Migdal parameters are derived from Skyrme energy functionals and compared with the phenomenological ones. We perform RPA calculations with various approximations for the Landau-Migdal particle-hole interaction and compare them with the results obtained with the full Skyrme interaction. For the first time the next to leading order in the Landau-Migdal approach is considered in nuclear structure calculations.Comment: Dedicated to the memory of G.E. Brow