274 research outputs found
Cereal cultivars innovations adapted to organic production: A new challenge
To face and better manage the development of new varieties in a society calling for more and more transparency, the French National Research Institute (INRA) has get involved in an ambitious reflexive program about the question of "impacts, acceptability and management of varietal innovations" engaging all its thematic research departments. New collaboration between social and technical sciences are promoted to produce, from exemplary case studies, generic concepts and tools to assess the different types of impact of a new variety. Breeding and management of new genetic materials adapted to organic farming conditions constitute an appropriate theme to develop such an integrated process. A pluridisciplinary research team, associating plant breeders, soil scientists, ecologists, agronomists, economists, sociologists, in close collaboration with professionals , will try to assess both the agroenvironmental and socioeconomic impacts of changes, by studying current dynamics around original durum wheat and rice cultivars adapted to organic production in different territories
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
SVOM pointing strategy: how to optimize the redshift measurements?
The Sino-French SVOM mission (Space-based multi-band astronomical Variable
Objects Monitor) has been designed to detect all known types of gamma-ray
bursts (GRBs) and to provide fast and reliable GRB positions. In this study we
present the SVOM pointing strategy which should ensure the largest number of
localized bursts allowing a redshift measurement. The redshift measurement can
only be performed by large telescopes located on Earth. The best scientific
return will be achieved if we are able to combine constraints from both space
segment (platform and payload) and ground telescopes (visibility).Comment: Proceedings of Gamma-Ray Bursts 2007 conference, Santa Fe, USA, 5-9
November 2007. Published in AIP conf. proc. 1000, 585-588 (2008
Relativistic correlation correction to the binding energies of the ground configuration of Beryllium-like, Neon-like, Magnesium-like and Argon-like ions
Total electronic correlation correction to the binding energies of the
isoelectronic series of Beryllium, Neon, Magnesium and Argon, are calculated in
the framework of relativistic multiconfiguration Dirac-Fock method. Convergence
of the correlation energies is studied as the active set of orbitals is
increased. The Breit interaction is treated fully self-consistently. The final
results can be used in the accurately determination of atomic masses from
highly charged ions data obtained in Penning-trap experiments.Comment: version soumise 3/08/200
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
La construction d’une démarche interdisciplinaire à partir de l’émergence de la céréaliculture biologique en Camargue: le projet CEBIOCA
La céréaliculture biologique apparait comme une alternative aux modes de production conventionnels, pour un nombre croissant d'agriculteurs de Camargue. Le programme CEBIOCA cherche à appuyer le développement de ce prototype d'agriculture en favorisant l'élaboration de pratiques agricoles pertinentes, la production de matériel végétal adapté et la mesure des impacts de la conversion à l'AB. Un groupe de travail interdisciplinaire, associant génétique, agronomie, malherbologie, écologie et sociologie s'est constitué à l'occasion de la réponse à l'appel d'offre CIAB et au cours de la première phase de fonctionnemet qui est présenté ici. Malgré certaines lacunes ou faiblesses dans la construction interdiciplinaire, les résultats font entrevoir des perspectives prometteuses,dans un contexte plus favorable, à condition que les partenariats scientifiques et professionnles soient renforcés
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
Coordinate-space approach to the bound-electron self-energy: Self-Energy screening calculation
The self-energy screening correction is evaluated in a model in which the
effect of the screening electron is represented as a first-order perturbation
of the self energy by an effective potential. The effective potential is the
Coulomb potential of the spherically averaged charge density of the screening
electron. We evaluate the energy shift due to a , ,
, or electron screening a , ,
, or electron, for nuclear charge Z in the range . A detailed comparison with other calculations is made.Comment: 54 pages, 10 figures, 4 table
Relativistic transition wavelenghts and probabilities for spectral lines of Ne II
Transition wavelengths and probabilities for several 2p4 3p - 2p4 3s and 2p4
3d - 2p4 3p lines in fuorine-like neon ion (NeII) have been calculated within
the multiconfiguration Dirac-Fock (MCDF) method with quantum electrodynamics
(QED) corrections. The results are compared with all existing experimental and
theoretical data
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
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