An integrated study of the development of organic rice cultivation in the Camargue (France)-

In the Camargue, rice and durum wheat are associated in rotations that have an ambivalent ecological impact: on the one hand, these two crops contribute to the preservation of the surrounding ecosystem, while on the other hand, when cropped intensively, they can threaten the ecological equilibrium of this protected area. In this context, organic agriculture would seem to be an alternative adopted by a certain number of producers and processors. However, the pioneers of this practice encounter numerous problems, both agronomic and economic. The study presented here aims: to construct a pluridisciplinary approach to analyse the conditions of the development of organic cereal cultivation in the Camargue: to identify the principal factors that limit the development of this new practice: to produce knowledge useful in helping ricegrowers put into practice organic cropping systems

Relativistic calculations of pionic and kaonic atoms hyperfine structure

We present the relativistic calculation of the hyperfine structure in pionic and kaonic atoms. A perturbation method has been applied to the Klein-Gordon equation to take into account the relativistic corrections. The perturbation operator has been obtained \textit{via} a multipole expansion of the nuclear electromagnetic potential. The hyperfine structure of pionic and kaonic atoms provide an additional term in the quantum electrodynamics calculation of the energy transition of these systems. Such a correction is required for a recent measurement of the pion mass

Dielectronic Resonance Method for Measuring Isotope Shifts

Longstanding problems in the comparison of very accurate hyperfine-shift measurements to theory were partly overcome by precise measurements on few-electron highly-charged ions. Still the agreement between theory and experiment is unsatisfactory. In this paper, we present a radically new way of precisely measuring hyperfine shifts, and demonstrate its effectiveness in the case of the hyperfine shift of $4s\_{1/2}$ and $4p\_{1/2}$ in $^{207}\mathrm{Pb}^{53+}$. It is based on the precise detection of dielectronic resonances that occur in electron-ion recombination at very low energy. This allows us to determine the hyperfine constant to around 0.6 meV accuracy which is on the order of 10%

Tensorial form and matrix elements of the relativistic nuclear recoil operator

Within the lowest-order relativistic approximation ($\sim v^2/c^2$) and to first order in $m_e/M$, the tensorial form of the relativistic corrections of the nuclear recoil Hamiltonian is derived, opening interesting perspectives for calculating isotope shifts in the multiconfiguration Dirac-Hartree-Fock framework. Their calculation is illustrated for selected Li-, B- and C-like ions. The present work underlines the fact that the relativistic corrections to the nuclear recoil are definitively necessary for getting reliable isotope shift values.Comment: 22 pages, no figures, submitted to J. Phys.

Exploring Biorthonormal Transformations of Pair-Correlation Functions in Atomic Structure Variational Calculations

Multiconfiguration expansions frequently target valence correlation and correlation between valence electrons and the outermost core electrons. Correlation within the core is often neglected. A large orbital basis is needed to saturate both the valence and core-valence correlation effects. This in turn leads to huge numbers of CSFs, many of which are unimportant. To avoid the problems inherent to the use of a single common orthonormal orbital basis for all correlation effects in the MCHF method, we propose to optimize independent MCHF pair-correlation functions (PCFs), bringing their own orthonormal one-electron basis. Each PCF is generated by allowing single- and double- excitations from a multireference (MR) function. This computational scheme has the advantage of using targeted and optimally localized orbital sets for each PCF. These pair-correlation functions are coupled together and with each component of the MR space through a low dimension generalized eigenvalue problem. Nonorthogonal orbital sets being involved, the interaction and overlap matrices are built using biorthonormal transformation of the coupled basis sets followed by a counter-transformation of the PCF expansions. Applied to the ground state of beryllium, the new method gives total energies that are lower than the ones from traditional CAS-MCHF calculations using large orbital active sets. It is fair to say that we now have the possibility to account for, in a balanced way, correlation deep down in the atomic core in variational calculations

Magnetic state of plutonium ion in metallic Pu and its compounds

By LDA+U method with spin-orbit coupling (LDA+U+SO) the magnetic state and electronic structure have been investigated for plutonium in \delta and \alpha phases and for Pu compounds: PuN, PuCoGa5, PuRh2, PuSi2, PuTe, and PuSb. For metallic plutonium in both phases in agreement with experiment a nonmagnetic ground state was found with Pu ions in f^6 configuration with zero values of spin, orbital, and total moments. This result is determined by a strong spin-orbit coupling in 5f shell that gives in LDA calculation a pronounced splitting of 5f states on f^{5/2} and f^{7/2} subbands. A Fermi level is in a pseudogap between them, so that f^{5/2} subshell is already nearly completely filled with six electrons before Coulomb correlation effects were taken into account. The competition between spin-orbit coupling and exchange (Hund) interaction (favoring magnetic ground state) in 5f shell is so delicately balanced, that a small increase (less than 15%) of exchange interaction parameter value from J_H=0.48eV obtained in constrain LDA calculation would result in a magnetic ground state with nonzero spin and orbital moment values. For Pu compounds investigated in the present work, predominantly f^6 configuration with nonzero magnetic moments was found in PuCoGa5, PuSi2, and PuTe, while PuN, PuRh2, and PuSb have f^5 configuration with sizeable magnetic moment values. Whereas pure jj coupling scheme was found to be valid for metallic plutonium, intermediate coupling scheme is needed to describe 5f shell in Pu compounds. The results of our calculations show that both spin-orbit coupling and exchange interaction terms in the Hamiltonian must be treated in a general matrix form for Pu and its compounds.Comment: 20 pages, LaTeX; changed discussion on reference pape

Third-order relativistic many-body calculations of energies and lifetimes of levels along the silver isoelectronic sequence

Energies of 5l_j (l= s, p, d, f, g) and 4f_j states in neutral Ag and Ag-like ions with nuclear charges Z = 48 - 100 are calculated using relativistic many-body perturbation theory. Reduced matrix elements, oscillator strengths, transition rates and lifetimes are calculated for the 17 possible 5l_j-5l'_{j'} and 4f_j-5l_{j'} electric-dipole transitions. Third-order corrections to energies and dipole matrix elements are included for neutral Ag and for ions with Z60. Comparisons are made with available experimental data for transition energies and lifetimes. Correlation energies and transition rates are shown graphically as functions of nuclear charge Z for selected cases. These calculations provide a theoretical benchmark for comparison with experiment and theory.Comment: 8 page

Relativistic quantum dynamics in strong fields: Photon emission from heavy, few-electron ions

Recent progress in the study of the photon emission from highly-charged heavy ions is reviewed. These investigations show that high-$Z$ ions provide a unique tool for improving the understanding of the electron-electron and electron-photon interaction in the presence of strong fields. Apart from the bound-state transitions, which are accurately described in the framework of Quantum Electrodynamics, much information has been obtained also from the radiative capture of (quasi-) free electrons by high-$Z$ ions. Many features in the observed spectra hereby confirm the inherently relativistic behavior of even the simplest compound quantum systems in Nature.Comment: Version 18/11/0