50 research outputs found
Consequences of the introduction of cereal - grain legume intercrops in the supply chain. Analysis from the perspective of farmers and cooperatives
Intercropping (the simultaneous growth of 2 or more species in the same field) is one way to solve some difficulties that organic supply chain has to face. The aim of this article is to assess the consequences and the compatibility with intercrops at 2 levels: i) cropping systems of 18 farmers from north of France and ii) the logistics ofagricultural cooperatives which collect durum wheat in Midi-Pyrenees altogether with two cooperatives that already had experimented intercrops (Terrena and AgriBioUnion).The conclusions of our work is that intercrops seem a priori compatible with farmersâ cropping systems and with the presentlogistic organization of cooperatives but the main difficulty remains the feasibility and the cost in sorting out grains. Constraints and benefits of intercrops must then be analyzed more precisely at each level of the supply chain in order to collectively develop solutions
Backward error analysis and the substitution law for Lie group integrators
Butcher series are combinatorial devices used in the study of numerical
methods for differential equations evolving on vector spaces. More precisely,
they are formal series developments of differential operators indexed over
rooted trees, and can be used to represent a large class of numerical methods.
The theory of backward error analysis for differential equations has a
particularly nice description when applied to methods represented by Butcher
series. For the study of differential equations evolving on more general
manifolds, a generalization of Butcher series has been introduced, called
Lie--Butcher series. This paper presents the theory of backward error analysis
for methods based on Lie--Butcher series.Comment: Minor corrections and additions. Final versio
Combinatorial Hopf algebras in quantum field theory I
This manuscript stands at the interface between combinatorial Hopf algebra
theory and renormalization theory. Its plan is as follows: Section 1 is the
introduction, and contains as well an elementary invitation to the subject. The
rest of part I, comprising Sections 2-6, is devoted to the basics of Hopf
algebra theory and examples, in ascending level of complexity. Part II turns
around the all-important Faa di Bruno Hopf algebra. Section 7 contains a first,
direct approach to it. Section 8 gives applications of the Faa di Bruno algebra
to quantum field theory and Lagrange reversion. Section 9 rederives the related
Connes-Moscovici algebras. In Part III we turn to the Connes-Kreimer Hopf
algebras of Feynman graphs and, more generally, to incidence bialgebras. In
Section10 we describe the first. Then in Section11 we give a simple derivation
of (the properly combinatorial part of) Zimmermann's cancellation-free method,
in its original diagrammatic form. In Section 12 general incidence algebras are
introduced, and the Faa di Bruno bialgebras are described as incidence
bialgebras. In Section 13, deeper lore on Rota's incidence algebras allows us
to reinterpret Connes-Kreimer algebras in terms of distributive lattices. Next,
the general algebraic-combinatorial proof of the cancellation-free formula for
antipodes is ascertained; this is the heart of the paper. The structure results
for commutative Hopf algebras are found in Sections 14 and 15. An outlook
section very briefly reviews the coalgebraic aspects of quantization and the
Rota-Baxter map in renormalization.Comment: 94 pages, LaTeX figures, precisions made, typos corrected, more
references adde
Peaâwheat intercrops in low-input conditions combine high economic performances and low environmental impacts
Intensive agriculture ensures high yields but can cause serious environmental damages. The optimal use of soil and atmospheric sources of nitrogen in cerealâlegume mixtures may allow farmers to maintain high production levels and good quality with low external N inputs, and could potentially decrease environmental impacts, particularly through a more efficient energy use. These potential advantages are presented in an overall assessment of cerealâlegume systems, accounting for the agronomic, environmental, energetic, and economic performances. Based on a low-input experimental field network including 16 site-years, we found that yields of peaâwheat intercrops (about 4.5 Mg haâ1 whatever the amount of applied fertiliser) were higher than sole pea and close to conventionally managed wheat yields (5.4 Mg haâ1 on average), the intercrop requiring less than half of the nitrogen fertiliser per ton of grain compared to the sole wheat. The land equivalent ratio and a statistical analysis based on the Price\u27s equation showed that the crop mixture was more efficient than sole crops particularly under unfertilised situations. The estimated amount of energy consumed per ton of harvested grains was two to three times higher with conventionally managed wheat than with peaâwheat mixtures (fertilised or not). The intercrops allowed (i) maintaining wheat grain protein concentration and gross margin compared to wheat sole crop and (ii) increased the contribution of N2 fixation to total N accumulation of pea crop in the mixture compared to pea sole crop. They also led to a reduction of (i) pesticide use compared to sole crops and (ii) soil mineral nitrogen after harvest compared to pea sole crop. Our results demonstrate that peaâwheat intercropping is a promising way to produce cereal grains in an efficient, economically sustainable and environmentally friendly way
Ătude des propriĂ©tĂ©s rhĂ©ologiques de suspensions dâalumine en prĂ©sence dâions divalents et dâacide polyacrylique
International audienc
Ătude des propriĂ©tĂ©s rhĂ©ologiques de suspensions dâalumine en prĂ©sence dâions divalents et dâacide polyacrylique
Les propriĂ©tĂ©s rhĂ©ologiques et d'agrĂ©gation de suspensions d'alumine ont Ă©tĂ© analysĂ©es dans des solutions contenant du calcium et un polyĂ©lectrolyte anionique (acide polyacrylique, PAA). Les expĂ©riences ont Ă©tĂ© rĂ©alisĂ©es prĂšs du pH de charge nulle de l'alumine (pH 9). A faible concentration d'ions calcium, le polyĂ©lectrolyte agit normalement comme un dispersant. L'addition de calcium favorise l'adsorption et diminue lĂ©gĂšrement la viscositĂ©, jusquâĂ la valeur 0,35 du rapport molaire calcium/motifs acryliques, oĂč la viscositĂ© et le seuil d Ă©coulement augmentent soudainement. Pour cette mĂȘme valeur du rapport, la formation du complexe calcium-PAA et l'adsorption du polyĂ©lectrolyte atteignent un maximum. Dans ces conditions, les mesures Ă©lectrocinĂ©tiques et les calculs de densitĂ© de charge montrent que les forces interparticulaires ne suivent pas de simples lois Ă©lectrostatiques, puisque la charge des particules est suffisante pour empĂȘcher l'agrĂ©gation. Ce phĂ©nomĂšne, qui n'est pas observĂ© en prĂ©sence d ions sodium Ă force ionique comparable, s'ajoute Ă d'autres expĂ©riences tendant Ă montrer que les ions calcium (et probablement d'autres ions multivalents) engendrent des forces attractives spĂ©cifiques entre des surfaces fortement chargĂ©es nĂ©gativement
Symmetril Moulds, Generic Group Schemes, Resummation of MZVs
The present article deals with various generating series and group schemes (not necessarily affine ones) associated with MZVs. Our developments are motivated by Ecalleâs mould calculus approach to the latter. We propose in particular a Hopf algebraâtype encoding of symmetril moulds and introduce a new resummation process for MZVs